Visceral mass and reticulorumen volume of differing biological types of beef cattle by Eddie L Fredrickson A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Range Science Montana State University © Copyright by Eddie L Fredrickson (1987) Abstract: A study was conducted to determine if differences in visceral organ mass and potential reticulorumen volume occur among beef cow biological types differing in milk production potential. During 1985» 6 pregnant, 6 to 9 yr old lactating cows of 5 biological types were used. These include: Straightbred Herefords (HH) , 50% Angus-50% Hereford (AH), 25% Simmental-75% Hereford (1S3H), 50% Simmental-50% Hereford (SH) and 75% Simmental-25% Hereford (3S1H). In 1986 , 6 pregnant, 3 yr old lactating cows of 4 biological types were examined: HH, 50% Tarentaise-50% Hereford (TH), 50% Tarentaise-(25% Simmental-25% Hereford) or 50% Tarentaise-(37.5% Simmental-12.5% Hereford)(T(SH)) and 50% Charolais-(25% Simmental-25% Hereford) or 50% Charolais-(37 • 3% Simmental-12.5% Hereford) (C(SH)). In the summer of 1985 fecal organic matter output was estimated with a CrgCL dilution technique (all cows) and total fecal collections (HH and 3a1H). Total fecal collections were obtained from all cows in 1986. Esophageal fistula collections were collected each fecal collection to estimate organic matter intake (OMI). Weightiheight ratios were used to determine body condition scores, and milk production estimates were obtained using a weigh-suckle-weigh technique. Weights of the spleen, heart, lungs, kidney, kidney fat, reticulorumen weight and volume and liver were measured 5 weeks after weaning in 1 985 and at weaning in 1986. Potential reticulorumen volume was determined to be the water filled capacity at slaughter. Differences (P>.10) in reticulorumen volume or OMI were not evident either year. In 1985 liver weight was greatest (P<.10) for the 3S1H and BH, and kidney weight was higher (P<.10) for the 3S1H. Cows with larger livers and kidneys also had lower (P<.10) condition scores and kidney fat weights. During 1986 milk production at weaning was greatest (P<.10) for the T(SH) and TH. Condition scores and body fat measurements did not differ (P>.10) in 1986. Kidney and spleen weights were highest (P< .10) for the C(SH) and tended to be high for the T(SH). Differences in kidney weight could be accounted for by differences in body weight, but differences in spleen weights are not understood. Differences in organ weights in 1985 appear to reflect milk production potential, while organ weights during 1986 possibly reflect both body size and milk production potential. Further research regarding metabolic activity per unit of tissue weight may further assist in understanding differences among biological types. VISCERAL MASS AND RETICULORUMEN VOLUME OF DIFFERING BIOLOGICAL TYPES OF BEEF CATTLE by E d d ie L . F r e d r i c k s o n A t h e s i s s u b m itte d i n p a r t i a l f u l f i l l m e n t o f t h e r e q u i r e m e n ts f o r t h e d e g r e e of M a s te r o f S c ie n c e in . Z Range S c ie n c e MONTANA STATE UNIVERSITY B ozem an, M ontana June 1987 MAIN Ub. Go^-cSO ii APPROVAL o f a t h e s i s s u b m itte d by E d d ie L . F r e d r i c k s o n T h is t h e s i s h a s b e e n r e a d by e a c h member o f t h e t h e s i s c o m m itte e and h a s b e e n fo u n d t o be s a t i s f a c t o r y r e g a r d i n g c o n t e n t , E n g lis h u s a g e , f o r m a t , c i t a t i o n s , b i b l i o g r a p h i c s t y l e , and c o n s i s t e n c y , and i s r e a d y f o r s u b m is s io n t o t h e C o lle g e o f G r a d u a te S t u d i e s . Im. a r i%AD a te | ] C h a i r p e r s o n , G ra d u a te C om m ittee A pproved f o r t h e M ajor D e p a rtm e n t c H ead, M ajor D e p a rtm e n t D a te A pproved f o r t (? D a te 2 C G ra d u a te Dean A ,. ill STATEMENT OF PERMISSION TO COPY In p re s e n tin g th is th e s is in p a rtia l fu lfillm e n t of th e r e q u i r e m e n ts f o r a m a s t e r 's d e g r e e a t M ontana S t a t e U n i v e r s i t y , I a g r e e t h a t th e L ib ra ry of th e s h a l l make i t L ib ra ry . w ith o u t s p e c i a l B rie f a v a ila b le q u o ta tio n s p e rm is s io n , p r o v id e d to from th a t b o rro w e rs u n d er th e r u le s th is th e s is a c c u ra te a re a ll o w a b l e a c k n o w led g e m en t o f t h e s o u r c e i s m ade. P e rm is sio n fo r e x te n s iv e q u o ta tio n from or r e p ro d u c tio n o f t h i s t n e s i s may be g r a n t e d by my m a jo r p r o f e s s o r , o r i n h i s a b s e n c e , by th e D i r e c t o r o f t h e L i b r a r i e s w hen, i n t h e o p i n io n o f e i t h e r , use o f th e m a te ria l i s fo r s c h o la rly p u rp o se s. th e th e s is m a te ria ls in th is w i t h o u t my p e r m i s s i o n . S ig n a tu re D a te fo r fin a n c ia l g a in t h e p ro p o s e d Any c o p y in g o r u se o f s h a l l n o t be a llo w e d iv ACKNOWLEDGEMENTS I w ould l i k e t o d e d i c a t e t h e e f f o r t s g r a n d p a r e n t s Mr. and M rs. C h a r le s W. F r e d r i c k s o n . h a v e b e l i e v e d i n m e, and i n my d e s i r e s c ie n c e . o f th e l a s t to T h ese tw o y e a r s t o fin e p e o p le p u r s u e an e d u c a t i o n i n r a n g e My g r a t i t u d e to w a rd them i s beyond w o rd s . my V TABLE OF CONTENTS P age LIST OF TABLES................................................................................................ ABSTRACT.......... ............................................................................'................,•-------• .............. v iii , INTRODUCTION......................................... .................. ...........................................................• I LITERATURE REVIEW.......................................................................... I n t r o d u c t i o n ................................................................................................... M a in te n a n c e Demand......................................................................................................... V i s c e r a l O rgan M ass....................................................................................................... A c tiv e T i s s u e s ............ ................................................................................ I n t a k e ...................................................................................................... R e tic u lo ru m e n v o lu m e .......... ........................................................................................ F a t i g u e ............................................................................ 3 4 7 11 16 MATERIALS AND METHODS.................................................................................... 1 M eth o d o lo g y Used i n 1 9 8 5 ................................................................................ M eth o d o lo g y Used i n 1 9 8 6 ....................................................................................... S t a t i s t i c a l A n a l y s i s .......... ...................................................................................... 19 23 24 RESULTS...................................................................................................................................... 1 9 8 5 ....................................................... ............- ....................... .................................... 1986 ................................................................................................ DISCUSSION............................................. F o ra g e I n t a k e .................................................................................................................. M ilk P r o d u c t i o n ............................................................................................................. O rgan M a ss......................................................................................................................... R e tic u lo ru m e n Volum e..................................................................... G e n e ra l D i s c u s s i o n ...................................................................................................... LITERATURE CITED............................................................................................................... APPENDIX............................................................................................................................ 26 26 42 42 44 45 47 50 60 vi LIST OF TABLES T a b le 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Page T r a i t s o f b e e f cow b i o l o g i c a l t y p e s , 1 9 8 5 . . . . .................................. 20 Body w e i g h t , body c o n d i t i o n , h ip h e i g h t , k id n e y f a t w e ig h t . and h o t c a r c a s s w e ig h t o f f i v e d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s , 1 9 8 5 ............................ 26 A verage d a i l y m ilk p r o d u c t i o n ( k g /d ) f o r f i v e b e e f cow b i o l o g i c a l t y p e s , 1 9 8 5 ...................................................... C a lf a v e ra g e d a i l y g a in (k g ) from dams o f f i v e b e e f cow b i o l o g i c a l t y p e s , 1 9 8 5 ................................. ' . 27 28 t S te p w is e r e g r e s s i o n c o e f f i c i e n t s f o r m ilk p r o d u c t i o n p r i o r w e a n in g , 1 9 8 5 ......................................................... 29 A v erag e d a i l y g a in (k g ) f o r f i v e d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s , 1 9 8 5 ...................................... 29 O rg a n ic m a t t e r i n t a k e p e r day (O M I/d, k g ) , and OMI/d a s a p e r c e n t o f body w e ig h t (%BW) f o r f i v e d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s , 1 9 8 5 . . ............ ......................... .................. - .............. 30 S te p w is e r e g r e s s i o n c o e f f i c i e n t s f o r o r g a n i c m a t t e r i n t a k e p r i o r t o w e a n in g , 1 9 8 5 ................................................................... 31 O rgan m ass o f f i v e d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s , 1 9 8 5 ............................ 32 O rgan m ass a s a p e r c e n t o f body w e i g h t, o f f i v e d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s , 1 9 8 5 . . . . .......................................................... 32 P o t e n t i a l r e t i c u l o r u m e n volum e o f f i v e d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s , 1 9 8 5 .............................................................. 33 Body w e i g h t, h i p h e i g h t , and h o t c a r c a s s w e ig h t o f f o u r d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s , 1986 ........................................... 34 K id n ey f a t w e ig h t, b a c k f a t t h i c k n e s s and m a r b lin g s c o r e o f f o u r d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s , 19 8 6 . . . . .............. 34 A v erag e d a i l y m ilk p r o d u c t i o n ( k g /d ) f o r f o u r b e e f cow b i o l o g i c a l t y p e s , 1986 ...................... ' . ................................................... ........... 35 C a l f a v e ra g e d a i l y g a in (Kg) from dams o f f o u r d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s , 1986 .................................................................... 36 vii LIST OF TABLES - C o n tin u e d T a b le 16 17 18 19 20 21 22 23 24 25 P age S te p w is e r e g r e s s i o n c o e f f i c i e n t s f o r m ilk p r o d u c t i o n a t . w e a n in g , 1986 ......................................................................................................... .. • 37 S te p w is e r e g r e s s i o n c o e f f i c i e n t s f o r m ilk p r o d u c t i o n a t w e a n in g , 1986 .................................... "•................................ ..................................... 37 A verage d a i l y g a in (k g ) o f f o u r d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s . 1986 ............................ 38 O rg a n ic m a t t e r i n t a k e p e r day (O M I/d, k g ) , and OMI/d a s a p e r c e n t o f body w e ig h (%BW) f o r f o u r b e e f cow b i o l o g i c a l t y p e s , 1986 ....................... 38 S te p w is e r e g r e s s i o n c o e f f i c i e n t s f o r o r g a n i c m a t t e r i n t a k e a t w e a n in g , 1986 ................................................................ 39 O rgan m ass o f f o u r d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s , 1986................................................................................. - .................................... . 40 O rgan m ass a s a p e r c e n t o f body w e ig h t ($BW) o f f o u r d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s , 1986 ........................................... 40 P o t e n t i a l r e t i c u l o r u m e n volum e o f f o u r d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s .......................... 41 L e a st s q u a re s a n a ly s is o f v a ria n c e o f o rg a n ic m a t t e r i n t a k e (O M I), 1 9 8 5 ............................... 61 L e a st s q u a re s a n a ly s i s o f v a ria n c e o f o rg a n ic m a t t e r i n t a k e (O M I), 1 9 8 6 .............. 61 v iii ABSTRACT A s tu d y w as c o n d u c te d t o d e te r m in e i f d i f f e r e n c e s i n v i s c e r a l o r g a n m ass and p o t e n t i a l r e t i c u l o r u m e n volum e o c c u r among b e e f cow b i o l o g i c a l t y p e s d i f f e r i n g i n m ilk p r o d u c t i o n p o t e n t i a l . D u rin g 1 9 8 5 , 6 p r e g n a n t , 6 t o 9 y r o ld l a c t a t i n g cow s o f 5 b i o l o g i c a l t y p e s w ere used. T h e se i n c l u d e : S t r a i g h t b r e d H e r e f o r d s ( H H ), 50% A n g u s-5 0 % H e r e f o r d (A H ), 25% S im m ental--? 5% H e r e fo r d (1 S 3 H ), 50% S im m e n ta l- 50% H e r e fo r d (SH) and 75% S im m ental-25% H e r e f o r d ( 3 S 1 H ) . In 1986, 6 p r e g n a n t , 3 y r o l d l a c t a t i n g cows o f 4 b i o l o g i c a l t y p e s w e re e x a m in e d : HH, 50% T a r e n t a i se-50% H e r e fo r d (T H ), 50% T a r e n t a i se -(2 5 % S im m ental-25% H e r e f o r d ) o r 50% T a r e n t a i s e - (37-5% S im m e n ta l- 12.5% H e r e f o r d ) ( T (S H )) and 50% C h a r o la is -( 2 5 % S im m ental-25% H e r e f o r d ) o r 50% C h a r o l a i s - ( 3 7 • 3% S im m e n ta l-1 2 .5 % H e r e f o r d ) (C ( S H ) ) . I n t h e summer o f 1985 f e c a l o r g a n i c m a t t e r o u tp u t w as e s t i m a t e d w ith a C r 2 Og d i l u t i o n t e c h n i q u e ( a l l cow s) and t o t a l f e c a l c o l l e c t i o n s (HH and 3 S 1H ). T o ta l f e c a l c o ll e c t i o n s w e re o b t a i n e d fro m a l l cows i n 1 9 8 6 . E so p h ag eal f i s t u l a c o l l e c t i o n s w ere c o l l e c t e d e a c h f e c a l c o l l e c t i o n t o e s t i m a t e o r g a n i c m a t t e r i n t a k e ( O M I). W e ig h tih e ig h t r a t i o s w e re u s e d t o d e te r m in e body c o n d i t i o n s c o r e s , and m ilk p r o d u c t i o n e s t i m a t e s w ere o b t a i n e d u s in g a w e i g h s u c k l e - w eig h t e c h n i q u e . W e ig h ts o f t h e s p l e e n , h e a r t , l u n g s , k i d n e y , k id n e y f a t , r e t i c u l o r u m e n w e ig h t and volum e and l i v e r w e re m e a su re d 5 w e e k s a f t e r w e a n in g i n 1 985 a n d a t w e a n in g i n 1 9 8 6 . P o te n tia l r e t i c u l o r u m e n volum e was d e te r m in e d t o be t h e w a t e r f i l l e d c a p a c i t y a t s l a u g h t e r . D i f f e r e n c e s ( P X I O ) i n r e t i c u l o r u m e n vo lu m e o r OMI w e re n o t e v id e n t e i t h e r y e a r . I n 1985 l i v e r w e ig h t w as g r e a t e s t (P < .1 0 ) f o r th e 3S1H and SH, an d k id n e y w e ig h t was h i g h e r (P < .1 0 ) f o r t h e 3S1H. Cows w i t h l a r g e r l i v e r s and k i d n e y s a l s o h a d lo w e r (P < .1 0 ) c o n d i t i o n s c o r e s and k id n e y f a t w e i g h t s . D u rin g 1986 m ilk p r o d u c t i o n a t w e a n in g w as g r e a t e s t (P < .1 0 ) f o r t h e T(SH) and TH. C o n d itio n s c o r e s and body f a t m e a s u re m e n ts d i d n o t d i f f e r ( P X 1 0 ) i n 1 9 8 6 . K id n e y and s p le e n w e i g h ts w e re h i g h e s t (P < .1 0 ) f o r t h e C(SH) and te n d e d t o b e h i g h f o r th e T (S H ). D i f f e r e n c e s i n k id n e y w e ig h t c o u ld be a c c o u n te d f o r by d i f f e r e n c e s i n body w e i g h t , b u t d i f f e r e n c e s i n s p l e e n w e ig h ts a r e n o t u n d e r s t o o d . D i f f e r e n c e s i n o r g a n w e ig h ts i n 1985 a p p e a r t o r e f l e c t m ilk p r o d u c t i o n p o t e n t i a l , w h ile o r g a n w e i g h ts d u r in g 1986 p o s s i b l y r e f l e c t b o th body s i z e and m ilk p r o d u c tio n p o t e n t i a l . F u r t h e r r e s e a r c h re g a rd in g m e t a b o li c a c t i v i t y p e r u n i t o f t i s s u e w e ig h t may f u r t h e r a s s i s t i n u n d e r s t a n d in g d i f f e r e n c e s among b i o l o g i c a l t y p e s . I INTRODUCTION A goal " m a x im iz e 1 9 8 6 ). of th e th e c o w -c a lf p o unds of th e s e tra its have h ig h e r e n e rg y re q u ire m e n ts m ust n u tritio n a lly re s tric tiv e c o n d itio n m a jo r be and fa c to r n e c e ssa ry to beef per cow i n ra n g e la n d s th e h e rd " m et cow p ro d u ce a ra n g e la n d l o w e r in g b ecause (T hom as, b e e f cow t y p e s w ith h ig h e r e ffic ie n c y o v e ra ll th e of Cow w e a n in g T h ese th a t d e m a n d in g . p e rfo rm a n c e o f te n by in e n e rg y e ffic ie n c y is and it of d iffe rin g g e n o ty p e is th e s e r e p ro d u c tiv e e n e rg e tic s h ig h e r A d e c lin e can o c c u r i f h e rd im p o rta n t 1 9 8 4 ). e n v iro n m e n t T h is d e c l i n e i n b e t t e r u n d e r s ta n d ty p e s (N E C , e n e rg e tic a lly re p ro d u c tiv e in c a lv e s to H ow ever, h i g h e r p r o d u c in g b e e f cow t y p e s in and is f o r m ilk p r o d u c t i o n and body s i z e . re q u ire m e n ts r e q u i r e m e n ts a r e n o t m e t. th e w eaned o f te n w e ig h ts (S m ith e t a l . , 19 7 6 ) . body w e s te rn To a c h ie v e t h i s g o a l p r o d u c e r s h a v e i n tr o d u c e d w ith a ls o on c a lf w ith h i g h e r g e n e t i c p o t e n t i a l ty p e s o p e ra to r m akes b io lo g ic a l e n v iro n m e n ta l in te ra c tio n s . A p p ro x im a te ly 70% o f th e m e ta b o liz a b le t h e a n im a l f o r m a in te n a n c e e n e rg y in ta k e ( F e r r e l and J e n k i n s , 1 9 8 5 ). is u se d by The r e m a in in g e n e rg y i s u s e d f o r a c t i v i t y , g r o w th , and c a l f p r o d u c t i o n . T ess e t a l . (1 9 8 4 ) w as re p o rte d fa s tin g heat p ro d u c tio n of m a in te n a n c e r e l a t e d t o t h e w e ig h t o f p r o t e i n i n t h e v i s c e r a o f p i g s . re s p o n s ib le fo r p ro te in and g a s t r o i n t e s t i n a l t u r n o v e r and i o n t r a c t h a v e p ro v e n t o tra n s p o rt h ig h ly V ita l o rg an s such a s th e liv e r be o f m a jo r im p o r ta n c e . F o r e x a m p le , l i v e r e x p e n d i t u r e s i n n o n l a c t a t i n g d a i r y cows w as e s t i m a t e d a t 3,369 k c a l/d , and a c c o u n te d fo r 2 2 .5 % of to ta l a n im a l e n e rg y 2 3,369 k c a l/d , e x p e n d itu re s w e ig h ts (S m ith m ay be e x p e n d itu re s th e s e ana a c c o u n te d fo r and B a ld w in , re la te d b e tw e en c h a n g e s may b e to 1 9 7 4 ). of in and to ta l T h erefo re d iffe re n c e s la c ta tin g fo u n d 2 2 .5 % in d a ta tis s u e s b e tw e e n r a n g e of th is b e e f cow t y p e s i s s o r t may r e f l e c t among cow t y p e s . The f i r s t changes in tis s u e co w s. beef l a c t a t i o n p o t e n t i a l s ( F e r r e l and J e n k i n s , 1 9 8 4 ) . th e s e e n e rg y m a in te n a n c e n o n la c ta tin g n o n la c ta tin g a n im a l e n e rg y A d d itio n a lly , cow s w ith d iffe re n t I n f o r m a t i o n c o m p a rin g u n a v a ila b le . H ow ever, d i f f e r e n c e s i n m a in te n a n c e r e q u i r e m e n ts o b je c tiv e of th is s tu d y w as t o m e a su re v i t a l o r g a n m ass o f ra n g e b e e f cow s w ith e m p h a s is on m ore m e t a b o l i c a l l y a c t i v e t i s s u e s and r e l a t e any d i f f e r e n c e s t o b e e f cow t y p e s o f v a r y i n g f o r a g e i n t a k e and m ilk p r o d u c t i o n . A lth o u g h th e re is a many la rg e g a s tro in te s tin a l fill fa c to rs am o u n ts tra c t may of fill m ech an ism s l i m i t i n t a k e lim it d a ta in ta k e w h ic h of low s u g g e s ts upon f o r a g e i n t a k e o f low q u a l i t y q u a lity th e ro u g h a g e i m p o r ta n c e (Van S o e s t , 1 9 8 3 ). of If f o r a g e s t h e n a n im a ls w i t h v a r y i n g i n t a k e am o u n ts may a l s o h a v e d i f f e r i n g r e t i c u l o r u m e n c a p a c i t i e s t o accom pany t h e i n c r e a s e i n by W agner e t a l . fo ra g e in ta k e s f o r a g e c o n s u m p tio n . I n an e a r l i e r s tu d y ( 1 9 8 6 ) , h i g h e r p r o d u c in g b i o l o g i c a l t y p e s had g r e a t e r th a n lo w e r p ro d u c in g d i g e s t i b i l i t i e s w e re b elo w 60 t o 65%. cow ty p e s w hen fo ra g e A s e c o n d o b j e c t i v e w as t o r e l a t e p o t e n t i a l r e t i c u l o r u m e n volum e w i t h cow ty p e and f o r a g e i n t a k e and t o d e te r m in e i f r e t i c u l o r u m e n volum e v a r i e s w ith f o r a g e i n t a k e . T h e se two o b j e c t i v e s w ould a llo w u s t o b e t t e r c h a r a c t 6 r i z e d i f f e r e n c e s among b e e f cow b i o l o g i c a l t y p e s and m a tc h a b i o l o g i c a l e n v ir o n m e n ta l c o n d i t i o n s . ty p e t o a s p e c i f i c s e t o f 3 LITERATURE REVIEW In tro d u c tio n O p tim a l b e e f cow p r o d u c t i v i t y th e e n e rg y tra n s fe r fro m th e fro m p la n t ra n g e la n d s com m unity to is d e p e n d a n t upon d e s ire d S p e c i f i c a l l y t h i s m eans p o u n d s o f c a l f w eaned p e r cow i n th e s a lv a g e v a lu e of th e p r o d u c in g a n im a ls . p ro d u c ts . t h e h e rd and To p ro d u c e a 454 kg s l a u g h t e r s t e e r G re g o ry (1 9 7 2 ) e s t i m a t e d t h a t 65% o f t h e n u t r i e n t s a r e u s e d t o s u p p o r t t h e c a l f t o w e a n in g a g e . F o r th e m a jo r ity o f p ro d u c e rs th is in n u trie n t r e q u ir e m e n t e n v ir o n m e n ts , B e s id e s s o la r each w ith m a n i p u la t in g e n e rg y e ffic ie n c y in of m u st a th e u n iq u e p la n t a d e s ira b le e n e rg y be m et set of com m unity fo rm , u tiliz a tio n a v a rie ty a ttrib u te s to of and a c h ie v e ra n g e la n d c o n s tra in ts . m a x im a l u s a b le c o n s i d e r a t i o n m ust be g iv e n t o by th e beef cow h e r d fo r th e o p tim a l p ro d u c tio n . E n e rg y u tiliz a tio n by t h e p r o d u c in g b e e f cow c a n be p a r t i t i o n e d i n t o m a in te n a n c e , g r o w th , t r a v e l , g e s t a t i o n and l a c t a t i o n H o w ev er, a rtific ia l among a l l beef as as s u g g e s te d e n e rg y C a s e b o lt, 1 9 8 4 ), Koong e t m e ta b o lis m p h y s io lo g ic a l cow b i o l o g i c a l by ra te of in (1 9 8 5 ) in v o lv e s p ro ce sse s. ty p e s a l. m ilk m a tu rity a B e c a u se com plex p a rtitio n in g is in te rre la tio n s h ip o f th e v a r i a b i l i t y p ro d u c tio n ( L a s te r th is (C o o k , 1 9 7 0 ). (H o tte r e t.a l., et 1 9 7 6 ), a l., body among 1978; s iz e (S m ith e t . a l . , 1976; H o t t e r e t . a l . , 1 9 7 8 ) , body c o m p o s itio n ( F e r r e l and J e n k in s , 1 9 8 4 ), re q u ire m e n ts fo ra g e (F e rre l in ta k e and (W agner e t.a l., J e n k in s , 1986) 1985) th e and m a in te n a n c e e x te n t and 4 in te rre la tio n s h ip To a c h ie v e among t h e s e o p tim a l p ro d u c tio n t h e r a n g e e n v iro n m e n t t o p o te n tia l. p h y s io lo g ic a l s u ffic ie n t p r o c e s s e s m u st a l s o v a ry . e n e rg y m ust be d e r i v e d su p p o rt each b io lo g ic a l t y p e 's fro m p h y s io lo g ic a l A g r e a t e r u n d e r s t a n d in g o f t h e m ech an ism s i n f l u e n c i n g t h e e x p r e s s i o n o f t h i s p h y s i o l o g i c a l p o t e n t i a l i n r e l a t i o n t o e n e rg y i n p u t s r e q u i r e d i n a r a n g e e n v iro n m e n t i s n e e d e d . in id e n tific a tio n and p o s s ib le T h is i n f o r m a t i o n may a s s i s t m a n ip u la tio n of b io lo g ic a l ty p e s e n e r g e t i c demand t o m a tc h t h e o f t e n l i m i t i n g r a n g e e n v ir o n m e n t. T h is r e v ie w o f l i t e r a t u r e w i l l be p r e s e n t e d i n r e q u i r e m e n ts v is c e ra l fo r o rg an th re e p a rts . m a in te n a n c e . m ass and its d i f f e r e n c e s among b i o l o g i c a l e x am in e re tic u lo ru m e n m echanism to s a tis fy w h ic h a d d r e s s e s The f i r s t T he th e p a r t w i l l d i s c u s s e n e rg y fo llo w in g p o s s ib le re la tio n t y p e s o f b e e f cow s. volum e d i f f e r e n c e s e n e rg e tic s t u d y 's o b j e c t i v e s p a rt to w ill e n e rg e tic The t h i r d among b i o l o g i c a l demand when ru m in a l a d d re ss fill demand p a rt w ill ty p e s a s a is lim itin g in ta k e . M a in te n a n c e Demand When e n e rg y u t i l i z a t i o n i s p a r t i t i o n e d a s s u g g e s te d by Cook (19 7 0 ) t h e e n e r g y f o r body s t a s i s o r m a in te n a n c e r e q u ir e m e n t i s 70 t o 75% o f t h e t o t a l a n n u a l e n e rg y r e q u ir e m e n ts 1 9 8 5 ). e n e rg y a p p r o x im a te ly ( F e r r e l and J e n k i n s , H ow ever, e s t i m a t e s by F e r r e l and J e n k i n s (1 9 8 5 ) o f t o t a l a n n u a l r e q u i r e m e n ts o f d i f f e r i n g b i o l o g i c a l c o n s id e ra b ly . t y p e s o f b e e f cow s v a r i e d T h e se e s t i m a t e s o f e n e rg y r e q u i r e d f o r m a in te n a n c e w ere d e r i v e d fro m f o u r b i o l o g i c a l t y p e s ; Angus X H e r e fo r d (AHX), C h a r o l a i s X 5 Angus o r H e r e fo r d (C X ), J e r s e y Angus o r H e r e f o r d (S X ). X Angus o r H e r e fo r d E ach cow was n i n e y e a r s o l d , and w as k e p t i n a n o n p re g n a n t, n o n la c ta tin g c o n d itio n . f o r m a in te n a n c e w as 1 3 0 , AHX, ( J X ) , S im m en tal X 129, CX, JX and SX co w s, The m e t a b o l i z a b l e e n e r g y r e q u i r e d 1 4 5 , and 160 k c a l x k g r e s p e c tiv e ly . T h e ir re s u lts '7 5 x d -1 in d ic a te fo r th a t m ilk p r o d u c t i o n p o t e n t i a l and m a in te n a n c e e n e rg y demand may be r e l a t e d f o r m a tu re cows e v e n when t h e p h y s io lo g ic a l demand o f l a c t a t i o n and g e s ta tio n a re n o t e v id e n t. R e s e a rc h i n v o l v i n g e n e r g y r e q u i r e m e n ts among b i o l o g i c a l t y p e s h a s been v a ria b le . m e ta b o lis m fo u n d no B rody b e tw e e n d a iry d iffe re n c e c ro ssb re d s te e r s . (1 9 4 5 ) d id not and b e e f in fin d d iffe re n c e s b ree d s. e ffic ie n c y K lo s te rm a n am ong R u s s e l and W rig h t H e re fo rd , in et re s tin g a l. (1 9 6 8 ) C h a ro la is and (1 9 8 3 ) r e p o r t e d no d i f f e r e n c e in m a in te n a n c e m e ta b o lis m b e tw e e n B lu e G rey and H e r e fo r d X F r i e s i a n cow s. W e b ste r F rie s ia n et a l. (.1974) p re d ic te d post a b s o rp tiv e m e ta b o lis m s t e e r s t o be p r o p o r t i o n a l l y 0 .0 6 tim e s g r e a t e r th a n X Angus s t e e r s . of F rie s a in V ercoe (1 9 7 0 ) and F r i s c h and V erc o e (1 9 7 6 ) d e te r m in e d Bos t a u r u s ( H e r e f o r d X S h o r th o r n and t h e r e c i p r o c a l c r o s s ) s t e e r s h ad a 10 to w e ig h t fo u n d 15% g r e a t e r (MBW) t h a n H o ls te in H e r e fo r d m a in te n a n c e per Bos i n d i c u s X Bos t a u r u s s te e rs s te e rs . r e q u ir e m e n t to have A d d itio n a l an b% s te e rs . in c re a s e re fe re n c e s u n it in c ite d m e t a b o li c G a rre tt (1 9 7 1 ) m a in te n a n c e by F e r r e l body over and J e n k i n s (1 9 8 5 ) s u g g e s t e d Bos i n d i c u s h a v e lo w e r m e t a b o li c r e q u i r e m e n t s p e r u n i t MBW th a n p o te n tia l Bos have ta u ru s . h ig h e r B io lo g ic a l m a in te n a n c e t y p e s w ith a h ig h m ilk re q u ire m e n ts , th a n b i o l o g i c a l t y p e s w i t h medium m ilk p o t e n t i a l . when p ro d u c tio n s c a le d to MBW, W e b s te r (1983.) f e l t 6 th a t fa s tin g m e ta b o lis m of c a ttle c o u ld b e ra n k e d a c c o r d in g t o th e ir r e s p e c t i v e l e v e l o f p r o d u c t i o n ; d a i r y cow s > b e e f b u l l s > b e e f s t e e r s > b e e f h e i f e r s > Z eb u . C hanges a s s o c ia te d in p h y s io lo g ic a l w ith c a lc u la te d la c ta tin g la rg e r e q u ir e m e n t n o n p reg n a n t n o n p reg n a n t H e re fo rd la s t flu x e s trim e s te r in of e n e rg e tic e n e rg y H e re fo rd fo r co w s m a tu r e dem and. m a in te n a n c e as when f e t a l g ro w th (Bauman and C u rrie , a s s o c i a t e d w ith t h e p o s tp a r tu m i n t e r v a l , is beef cow a r e F o r e x a m p le , th e 31% h i g h e r fo r is co m p ared a b o u t 75% g r e a t e r i n t h e a n im a l th e cow s ( N e v i l l e and M c C u llo u g h , o f g e s ta tio n r e q u i r e m e n ts a r e n o n p reg n a n t of s ta tu s to n o n la c ta tin g , 1969) • D u rin g t h e g re a te s t, n u trie n t p r e g n a n t a n im a l t h a n i n t h e 1.980). O th e r e n e rg y c o s ts su c h a s i n v o l u t i o n , a l s o h a v e a com pounding e f f e c t w ith p e a k m e t a b o li c dem ands a s s o c i a t e d w ith e a r l y la c ta tio n . M a in te n a n c e w ith d e c re a s in g W r ig h t, r e q u i r e m e n ts body 1 9 8 3 ). In c o n d itio n in c o n d itio n th r o u g h su bsequent th e c o n d itio n a d d itio n N o rth e rn th e d e c re a se have been (K lo s te m a n G re a t P la in s (Adam s, re p ro d u c tiv e d e te r m in e d et cows e n t e r i n g w in te r in a ls o a l., to 19 6 8 ; d e c re a se R ussel t h e w i n t e r m o n th s i n o fte n re ta in e d 1 9 8 7 ) , w hich o f t e n p e rfo rm a n c e poor re s u lts ( B e llo w s and and poor body in a S h o rt, 1 9 7 8 ) , m ilk p r o d u c t i o n and c a l f g ro w th ( C o r a h , 1 9 8 0 ). E ffe c ts m e ta b o lis m shown t o of of e n v ir o n m e n t beef cow s. a ffe c t re s tin g a ls o P rio r cau se s h ifts e x p o s u re m e t a b o li c r a t e s . to in c o ld th e m a in te n a n c e te m p e ra tu re s Cows k e p t i n c o ld have c h a m b e rs w ith e x p o s u re o f 20 C h a d a r e s t i n g m e t a b o li c r a t e o f a p p r o x im a te ly 70 kcal x W x d~\ w h e re a s cows e x p o s e d to -2 0 C had a re s tin g 7 m e ta b o lis m of a p p r o x im a te ly 110 k c a l M a in te n a n c e e n e rg y i n c r e a s e s due t o x W” " ^ x d“ ^ th e d i s s i p a ti o n (Y oung, 1 9 7 5 ). o f h e a t w ith h e a t s t r e s s , h a v e b e e n n o te d ( M o r r is o n , 19 8 3 )• D a ily e n e rg y e x p e n d i t u r e s a s s o c i a t e d w ith tra v e l and g r a z i n g fo r t h e f r e e ro a m in g b e e f cow a r e s i g n i f i c a n t l y h i g h e r th a n f o r t h e h o u se d cow ( B l a x t e r , e x p e n d itu re s 1 9 6 2 ). E s tim a te s ro a m in g a n im a l a r e v a r i a b l e . of e n e rg y fo r th e fre e H a v s ta d a n d M alech ek (1 9 8 2 ) b e l i e v e d t h i s i n c r e a s e may be a s h ig h a s 40%, w h ile O s u j i (1 9 7 4 ) g i v e s a r a n g e o f 25 t o 50%. O th e r e s t i m a t e s a r e a s h ig h a s 100% ( O s u j i , 1 9 7 4 ) . The e f f e c t o f p re v io u s n u t r i t i o n b e e n d e m o n s tr a te d i n r a t s a l., 1 9 8 6 ). in d ic a te d h ig h a C hanges i n th e s e a s p re v io u s le v e l c o r r e s p o n d in g body s iz e in c re a s e d id m a in te n a n c e r e q u i r e m e n t , heat p ro d u c tio n has ( F e r r e l and K oong, 1982) an d s h e e p ( F e r r e l e t A summary o f th a t on f a s t i n g not in e x p e r im e n ts by Koong e t of n u tritio n w as v a r i e d m a in te n a n c e appear to be a a l. fro m low t o re q u ire m e n t fa c to r in (1 9 8 5 ) o c c u rre d . c h a n g in g t h e s i n c e a l l a n im a ls w e re ra n d o m ly r e a s s i g n e d t o d i f f e r e n t n u t r i t i o n a l l e v e l s midway th r o u g h t h e s t u d y . V i s c e r a l O rgan Mass I n o r d e r t o u n d e r s t a n d t h e i n f l u e n c e m a in te n a n c e e n e rg y demand may h a v e on v i s c e r a l t i s s u e s e n e rg y e s s e n tia lly e n e rg y i s it is re p re s e n ts i m p o r ta n t t o th e used f o r c i r c u l a t i o n , "co st rem em ber t h a t m a in te n a n c e of life " re s p ira to ry ( D a le , fu n c tio n , 19 8 4 ) . c e llu la r T h is re p a ir and r e p l a c e m e n t, membrane t r a n s p o r t , dynam ic e q u i l i b r i u m and many o t h e r fu n c tio n s at b o th th e c e llu la r and tis s u e le v e l. B ecause of th e 8 v a ry in g ro le e n e rg e tic (L o b le y of v ita l o rg an s c o s t. D a ta a l., 1980; et in m a in te n a n c e p re s e n te d each by B a ld w in e t E d d e ls to n e and o rg an , h a s a l. H olzm an, (1 9 8 0 ) 19 8 1 ; its own and o t h e r s C anas et a l., 1982) d e m o n s tr a te d t h a t i n d i v i d u a l t i s s u e s e a c h h a v e a u n iq u e m e t a b o li c dem and. I n w ork by C anas e t a l . (1 9 8 2 ) h e a t p r o d u c t i o n p e r gram o f t i s s u e i n r a t s w as 10 tim e s g r e a t e r i n th e w e ig h t a c tiv itie s and re s tin g in te s tin e s w ere o x id a tiv e g re a te r in liv e r la c ta tin g th a n i n of m u s c le . B o th t h e th e s u b je c ts h e a rt, th a n in liv e r and n o n la c ta tin g a n im a ls . F u r th e r m o r e , a 24% i n c r e a s e i n m a in te n a n c e e n e rg y r e q u i r e m e n ts w ere e x p la i n e d liv e r. S tu d ie s c o n s u m p tio n in a c c o u n te d f o r le s s by d i f f e r i n g et a l. by E d d e ls to n e n e w b o rn 15 and (1 9 8 4 ) r e l a t i v e w e i g h ts o f t h e h e a r t , and la m b s H o ltzm an fo u n d th a t 11%, r e s p e c t i v e l y , d e te r m in e d fa s tin g (1 9 8 1 ) th e of heat tis s u e liv e r o f th e t o t a l k id n e y and and GI oxygen tra c t ox y g en consum ed, p ro d u c tio n w as h ig h ly c o r r e l a t e d t o t h e w e ig h t o f p r o t e i n i n t h e v i s c e r a and b lo o d i n p i g s . G a rlic k m e t a b o li c et ra te a l. in (1 9 7 6 ), p ig s , t u r n o v e r and s y n t h e s i s . c itin g ra ts In h is s tu d y w ith s y n t h e s i s w as g r e a t e s t liv e r GI s y n th e s is th e tra c t e x h ib it (L o b le y e t a l . , p ro te in s y n th e s is in s tu d ie s , and man w e re h i g h l y o f p ro te in and o th e r th e 1 9 8 0 ). th e c a ttle in th e v is c e r a . g re a te s t ra te of s ta te d re la te d th e th a t to th e p ro te in fra c tio n a l ra te Of t h e v i s c e r a t h e fra c tio n a l p ro te in M u scle a c c o u n te d f o r t h e m a j o r i t y o f w h o le a n im a l. L o b le y et a l. (1 9 8 0 ) b e l i e v e d t h e w ork o f p r o t e i n s y n t h e s i s r e p r e s e n t s a maximum o f 30% o f th e to ta l a n im a l e n e rg y e x p e n d itu re s . B a ld w in and S m ith (1 9 7 5 ) 9 s u g g e s te d p ro te in m e ta b o lis m a c c o u n ts fo r 20 to 25% o f liv e r e n e rg y e x p e n d itu re s . The a c t i v e m ovement o f i o n s a c r o s s b i o l o g i c a l m em branes i s a n o t h e r s ig n ific a n t so u rc e of e n e rg y M c B rid e u tiliz a tio n M illig a n and (1 9 8 5 ), tra n s p o rt o f Na+ and K+ , s t a t e d in d e s c rib in g th e th e in v is c e ra v itro p e r c e n ta g e of c a ttle . m e a s u re m e n ts of re s p ira tio n fo r due t o t r a n s p o r t f o r s k e l e t a l m u s c le , d u o d e n a l e p i t h e l i u m and h e p a t o c y t e s w ere 26 t o 46%, 28 t o 61%, and 18 t o 54%, r e s p e c t i v e l y . The n e rv o u s s y s te m and th e s e k id n e y e s tim a te d h ad even v a lu e s h ig h e r b e in g cost 50 t o of tra n s p o rtin g 60% (B a k e r and C o n n e lly , ( B a la b a n e t a l . , 1 9 8 0 ) , r e s p e c t i v e l y . a c tiv ity 1966) w ith and 70% M ajo r s i t e s o f Na+ , K+ - ATPase (enzym e c a t a l y z i n g t h e a c t i v e pum ping o f Na+ and K+ a c r o s s t h e p la s m a m em brane) a r e s y s te m io n s , and in duodenal c o n s u m p tio n 10 t o h e p a to c y te s (M cB ride c o n s u m p tio n of th e k id n e y , liv e r, e p ith e liu m . 42% f o r th e fed and M i l l i g a n , O2 b e tw e e n la c ta tin g T h is a n im a l s k e le ta l a c tiv ity over 1 9 8 5 a ). and m u sc le s, In d ry in c re a s e d th e fa s te d a s tu d y e w e s, n e rv o u s O2 a n im a l o f th e Na+ , K+ - in liv e r ATPase d e p e n d e n t a c t i v i t y a c c o u n te d f o r 45 and 37% o f t h e O2 c o n s u m p tio n r a t e , r e s p e c t i v e l y , a n i n c r e a s e o f 22% w i t h l a c t a t i o n 1 9 8 5 b ). I n c r e a s e s i n O2 c o n s u m p tio n by t h e l i v e r , k id n e y o f c o ld s t r e s s e d r a t s - ATPase a c t i v i t y s tu d ie s (M cB ride and M i l l i g a n , th a t w e re c o m p le te ly a c c o u n te d f o r by Na+ , K+ (G u e rn s e y and S t e v e n s , e n e rg e tic cost s k e l e t a l m u sc le and of 19 7 7 )• Na+ , K+ - It ap p e ars ATPase a c t i v i t y from t h e s e is c lo s e ly t ie d to p h y s io lo g ic a l s ta t u s . A f u r th e r in d ic a to r o f p h y s io lo g ic a l s t a t u s i s v is c e ra l e n e rg e tic s i n v a r y i n g b lo o d flo w r a t e s . change w ith B lo o d flo w r a t e s 10 in c re a s e 50 la c ta tio n to in in c re a s in g 60$ cows ra te m e ta b o liz a b le B a ird , 1 9 8 3 ). b lo o d f lo w th e d ig e s tiv e (Lomax and B a i r d , of flo w e n e rg y T h is to p ro d u c tio n . to to th e in ta k e is liv e r to th e In a d d itio n and GI and a g re e m e n t w i t h w ith and 19 8 3 )• ( H u n tin g to n in in c re a s e tra c t tra c t R e y n o ld , S e lle rs in c re a s e s in liv e r th e re w ith is an w ith in c re a s e d 1986; Lomax and ( 1965) v o la tile who fo u n d fa tty a c id I n c r e a s e d b lo o d flo w r a t e s i n d i c a t e h i g h e r O2 c o n s u m p tio n , g r e a t e r CO2 rem o v a l from t h e t i s s u e , an i n c r e a s e i n b lo o d m e t a b o l i t e s , and g r e a t e r w ork l o a d s i n v o l v i n g a c t i v i t i e s s u c h a s b lo o d p u r i f i c a t i o n and b lo o d c e l l t u r n o v e r . R e s e a rc h in v o lv in g changes in th e o r g a n m ass o f c a ttle e f f e c t on m a in te n a n c e e n e rg y e x p e n d i t u r e s w as p r o b a b ly f i r s t by S m ith and B a ld w in (1 9 7 4 ). in v o lv in g e n e rg y its p e rfo rm e d C i t i n g e a r l i e r w ork o f B a r c r o f t ( 1 9 4 7 ) , B ard ( 1 9 6 1 ) , L i n z e l l ( I 9 6 0 ) , N e u tz e e t a l . (1 9 6 2 ) and ( 1 9 6 8 ) , and Wade and B is h o p c o n s u m p tio n by t i s s u e s , th e y d e te r m in e d t h a t t h i s m ig h t b e e s p e c i a l l y t r u e o f t h e m ore m e t a b o l i c a l l y a c t i v e t i s s u e s . T h ese t i s s u e s in c lu d e g a s tro in te s tin a l c a ttle , b o th th e l i v e r , (G I) t r a c t . la c ta tin g and h e a r t , mammary and co m p o n e n ts o f t h e D a ta fro m two b i o l o g i c a l t y p e s o f d a i r y n o n la c ta tin g , i n c r e a s e i n t i s s u e w e i g h ts w i t h l a c t a t i o n la rg e r body s iz e and g r e a t e r la c ta tio n d e m o n s tra te d a g e n e ra l and i n b i o l o g i c a l t y p e s w i t h p o te n tia l ( S m ith and B a ld w in , 1 9 7 4 ). D a ta of o rg an w e ig h ts in c o n ju n c tio n w ith a d d itio n a l d a ta r e g a r d i n g t i s s u e e n e rg y c o n s u m p tio n w ere u s e d t o e s t i m a t e t h e i n f l u e n c e o f t i s s u e w e ig h ts upon m a in te n a n c e r e q u i r e m e n ts b e tw e e n l a c t a t i n g n o n l a c t a t i n g cows (S m ith and B a ld w in , 1 9 7 4 ). and I n c r e a s e s w ith l a c t a t i o n 11 i n t h e w e i g h ts o f t h e GI t r a c t , l i v e r , h e a r t , mammary g l a n d , and o t h e r c o m p o n e n ts not s p e c ifie d (S m ith and B a ld w in , in c re a s e d 1 9 7 4 ). m a in te n a n c e The g r e a t e s t r e q u i r e m e n ts changes in by o r g a n w e ig h t and p e r c e n t e n e rg y c o n s u m p tio n w as n o te d f o r t h e mammary, GI t r a c t , and h e a r t w i t h e s t i m a t e d g re a te r, change re s p e c tiv e ly in in c re a s e a b s o lu te n o n la c ta tin g to ta l e n e rg y 22.5% cow c o n s u m p tio n b e in g (S m ith and B a ld w in , o f 851 k c a l / d . a c c o u n te d ^ f o r tra c t, e n e rg y of and c o n s u m p tio n In t h i s th e to ta l 25.6% in and h e a r t r e p r e s e n t e d e n e rg y e x p e n d i t u r e s s tu d y w as 20 and 19% However t h e g r e a t e s t fo r th e e n e rg y la c ta tin g 2 . 3 , 7 .2 liv e r liv e r w ith an t h e l i v e r e n e rg y e x p e n d i t u r e s a n im a l th e 50, 22, 1 9 7 4 ). 10% e x p e n d itu re s cow . in th e The mammary, and 10.0% , r e s p e c t i v e l y , GI o f th e f o r m a in te n a n c e i n t h e n o n l a c t a t i n g a n i m a l , and 3 . 6 , 8 .4 and 1 1 .9 , r e s p e c t i v e l y , i n t h e l a c t a t i n g a n im a l (S m ith and B a ld w in , 1 9 7 4 ) . A c tiv e T i s s u e s The f u n c t i o n o f t h e h e a r t i s t h e c i r c u l a t o r y s y s te m . m ass i n not resp o n se due t o (Z a k , to 19 7 3 )• W h ile t h e h e a r t i n t h e a d u l t a n im a l can c h a n g e lo n g te rm an in c r e a s e t h e p r o p u l s i o n o f t h e b lo o d t h r o u g h in in c re a s e d th e w ork l o a d s t h i s num ber o f c e lls P r e s e n t k n o w led g e o f t h e h e a r t i s p resen t c e lls a lre a d y in te rc e llu la r th e re fo re d e c re a se d d iffe re n tia te d . s tru c tu re s such a g re a te r e n e rg y to " n o rm a l" m y o c a r d ia l T h is as w ould mean m ito c h o n d ria dem and. c e lls When t h e w ill in g e n e ra lly th e h e a rt t h a t m y o c a r d ia l c e l l s do n o t r e g e n e r a t e i n t h e a d u l t a n im a l, b u t t h a t t h e r e i s of is an (Z a k , h e a r t 's re tu rn to a e n la r g e m e n t in c re a s e 1 9 7 3 ), and w o rk lo a d n o rm al in is s iz e 12 ( B e z n a k , 19 6 9 )• In th e c a s e o f w o rk lo a d s b elo w n o rm a l a tr o p h y o f t h e h e a r t c a n o c c u r ( K n ig h t, 1 9 6 7 ) . The s p le e n se rv e s as a s to ra g e a re a fo r b lo o d u n til su c h tim e b lo o d i s n e e d e d f o r o t h e r f u n c t i o n s . . B e c a u se o f t h i s f u n c t i o n s i z e o f th@ s p le e n c a n v a r y q u i c k l y w i t h i n a i n d i v i d u a l d e p e n d in g on t h e am ount o f b lo o d i n t h e s p l e e n . The s p l e e n i s n o t an e s s e n t i a l o r g a n a s o t h e r o rg an s fu n c tio n s can fu n c tio n s assu m e of c o rp u s c le s , th e its s p le e n in c lu d e ; p ro d u c tio n of if th e re m o v a l s p le e n of ly m p h o c y te s , e n e rg y c o n s u m p tio n of th e com pared t o o t h e r t i s s u e s (B a rc ro ft, Lung volum e and d i f f u s i o n su rfa c e p ro p o rtio n a l to body w e ig h t aged rem o v e d . or dead p ro d u c tio n f o r m a tio n o f b i l e p ig m e n t and s t o r a g e o f i r o n T he is lu n g s of O th e r red b lo o d a n tib o d ie s , (S w e n so n , 1 9 8 3 ). a p p e ars to be m in im a l as 1947; a s c i t e d by B l a x t e r , 19 6 2 ) . a r e a f o r g a s e x c h a n g e a p p e a r s t o be (R e e ce , 1 9 8 3 ). T h is i s in d ic a te d by th e te n d e n c y to w a rd s i n c r e a s e d w id th and d e p th o f t h e b r i s k e t w ith h e a v i e r b io lo g ic a l ty p e s . The k i d n e y 's h ig h r a t e o v e r a l l m e ta b o lis m . o f b lo o d flo w in d ic a te s its im p o r ta n c e t o The a v e r a g e b lo o d flo w t o t h e k i d n e y s o f s h e e p and g o a t s w as m e a su re d a s b e in g 550 ml x m in” ^ x IOOg t i s s u e . B lood f lo w s f o r t h e l i v e r and s k e l e t a l m u sc le a r e 320 and 5 ml x m in- ^ x IOOg tis s u e - ^, fu n c tio n re s p e c tiv e ly is (V ern o n m a in ta in in g b lo o d and io n P e a k e r, 1 9 8 3 ). e q u ilib riu m , c o n t r i b u t i o n t o t h e e n e rg y e x p e n d ed by t h e s e o r g a n s . p la y a ro le e x c re tio n . in p ro te in m e ta b o lis m , T w enty p e r c e n t of in c lu d in g g ly c o g e n e s is a t t r i b u t e d t o t h e k id n e y (80% i n t h e l i v e r ) . u rea in th e A m a jo r a k id n e y s ig n ific a n t The k id n e y s a l s o c o n s e rv a tio n fa s tin g a n im a l and is P r o d u c ti o n o f g l u c o s e i n 13 th e k id n e y an d t h e l i v e r a s g lu c o s e in c lu d e is s h o u ld i n c r e a s e s u b s t a n t i a l l y a p rec u rso r fo r la c to s e . m a in ta in in g w a te r b a la n c e , w ith l a c t a t i o n O th e r f u n c t i o n s o f t h e k id n e y e lim in a tio n of c o m p le x o rg a n ic com pounds and m e ta b o lis m and s e c r e t i o n o f e n d o c r in e s u b s t a n c e s . L iv e r fu n c tio n s in c lu d e l i p i d a re d iv e rs e and m u ltifa c e te d . T h e se fu n c tio n s m e ta b o lis m , c a r b o h y d r a te m e ta b o lis m , p r o t e i n m e ta b o lis m , horm one d e g r a d a t i o n an d p r o d u c t i o n , b i l e p r o d u c t i o n , b lo o d p u r i f i c a t i o n and e l i m i n a t i o n e n e rg e tic th e of to x ic s u b s ta n c e s . M ajor p r o c e s s e s a c c o u n t in g f o r demand h a v e b e e n p r e v i o u s l y liv e r c a n be s e v e re ly m e n tio n e d . im p a c te d b y fa s tin g S iz e s in c e m a jo r s i t e f o r s t o r a g e o f b o th p r o t e i n and g ly c o g e n . fo r 2 to 8% o f n u tritio n a l th e w et w e ig h t of th e a n im a l. s ta tu s 24 h o u rs th e T h is rese rv e w ith in a d d itio n , s ta r v a tio n o r p ro te in d e f ic ie n t d i e t s days o f f a s tin g fa s tin g liv e r d e p le te d l o s s o f l i v e r p r o t e i n w ith of of (B e itz and w e ig h t o f th e liv e r is a G ly c o g e n a c c o u n t s d e p e n d in g of upon g ly c o g e n and A l l e n , can 1 9 8 3 ). c a n c a u s e up t o th e g r e a t e s t lo s s w ith in th e f i r s t th e be In a 40%. se v era l (V ern o n and P e a k e r , 1 9 8 3 ). U n lik e o t h e r v i t a l o r g a n s o f t h e b e e f cow t h e rum en h a s r e c e i v e d a v o lu m in o u s am ount o f a t t e n t i o n . s p le e n th e rum en is a m u s c u la r In c o n tra s t to o rg an . The t h e l i v e r , k id n e y s and rum en is n e c e ssa ry m ix in g , e v a c u a t i o n and r e g u r g i t a t i o n c o n t r a c t i o n s t o f a c i l i t a t e and d ig e s tio n of th e c o n tin u o u s b u t v a r y i n ru m in a l c o n te n ts . o f a c t i v i t y an d r e s t ( R uckebusch, 1 9 8 0 ). cow 6 t o c o n tra c tio n s ( D z iu k , 8 b ip h a s ic 1 9 8 3 ). T hese ) f r e q u e n c y and i n t e n s i t y A d o u b lin g of p assag e c o n tra c tio n s b e h a v io ra l a re s ta te s In a r e s t i n g , p o st a b s o rp tiv e p er fiv e th e w ith fo r m in u te p e r i o d re s tin g ra te is s h o u ld n o te d fo r occur sh eep 14 d u r in g f e e d i n g , h ay d ie ts and t h e over cu b ed num ber o f c o n t r a c t i o n s hay d ie ts ( R uckebusch, a re g r e a t e r f o r lo n g 1 9 8 0 ). The e n e r g e t i c demand a s s o c i a t e d w i t h i n c r e a s e d r u m in a l c o n t r a c t i o n s e x p l a i n s i n th e i n c r e a s e d w ork o f d i g e s t i o n a s n o te d by O s u ji (1 9 7 3 ; p a rt a s c ite d by O s u j i , 1 9 7 4 ). F e ll and W eekes (1 9 8 0 ) d is c o v e re d a c lo s e re la tio n s h ip fo o d i n t a k e an d t h e w e ig h t o f r u m in a l m u co sa . In cre a se d b e tw e e n la c ta te an d p y r u v a t e f o r m a ti o n w h ic h o c c u r r e d d u r i n g p e r i o d s o f p e a k i n t a k e r a t h e r th a n d u r in g peak la c ta tio n su g g est th a t th e a c tiv ity of m ucosa i s m e d ia te d by i n t a k e r a t h e r th a n m e t a b o li c dem and. change in r u m in a l tis s u e in v o lv e d . e p ith e lia l w e ig h t was However an in c re a s e due in to c e ll th e r u m in a l Most o f t h e h y p e rtro p h y of th e nu m b ers a c c o u n te d fo r some w e ig h t i n c r e a s e w i t h a h ig h c o s t o f m i t o t i c c e l l d i v i s i o n , y e t an i n c r e a s e i n c e l l n um bers w as n o t a s e v i d e n t . In ta k e To m ee t t h e consum e z e ro , a c h a n g in g e n e rg y dem ands o f m a in te n a n c e c o r r e s p o n d in g am ount of o r p o s i t i v e e n e rg y b a la n c e o f fo o d consum ed i s n u trie n t and a v a ila b ility d e n s ity , p h y s ic a l e n e rg y ( B a i l e and F o r b e s , d e p e n d a n t upon a t t r i b u t e s c a lo ric and m e ta b o liz a b le of th e to m a in ta in 1 9 7 4 ) . The am ount o f th e fo ra g e in c lu d in g d ig e s tib ility lim ita tio n s a n im a ls m ust of th e a n im a l. fee d , In fo ra g e a ra n g e e n v iro n m e n t w h e re f e e d s a r e o f t e n f i b r o u s , b u lk y and o f v a r i a b l e a v a ila b ility , th e c a p a c ity of th e ru m en , p assag e ra te s and fa tig u e 15 r e s t r i c t i o n s a s s o c i a t e d w ith g r a z i n g becom e l i m i t i n g f a c t o r s o f f o r a g e in ta k e . N u m erous w ith re se a rc h e rs th e in c re a s e d la c ta tin g c ro ssb re d cows o f t h e cow s fo u n d demand consum ed a l., in tw o 1971; o ld re s p e c tiv e ly . h e ife rs fo u n d 1 9 8 5 ). 49% m o re a s s o c ia te d For th a n e x a m p le , n o n la c ta tin g S im ila r d iffe re n c e s a n im a ls by o t h e r H odgson la c ta tin g R o is e r e e t a l . co nsum ed fo ra g e 1 9 8 6 ). consum ed 76 an d 43% m ore th a n n o n l a c t a t i n g fa ll, in ta k e and n o n la c t a t i n g A llis o n , e x p e rim e n ts in la c ta tio n . 40% m ore (K ro n b e rg e t (D ijk s tra , in c re a s e s d u rin g fo u n d b e tw e e n l a c t a t i n g re se a rc h e rs (1 9 8 1 ) n u trie n t same h e r d have been have cow s and J a m ie s o n (M arched a n im a ls d u r i n g c a lv e d ) s p rin g and (1 9 8 0 ) fo u n d t h a t l a c t a t i n g 2 y e a r fo ra g e th a n th e ir n o n la c ta tin g c o u n te rp a rts . F o ra g e i n t a k e h a s a l s o b e e n fo u n d t o v a r y b e tw e e n b i o l o g i c a l t y p e s on summer r a n g e l a n d s . s tra ig h tb re d c o n su m e d H e re fo rd s 1 .9 r e s p e c tiv e ly . and K ro n b e rg et a l. (1 9 8 6 ) re p o rte d (HH) and 3 / 4 S im m e n ta ls X 1 /4 H e r e f o r d s 2 .1 % of th e ir W agner e t a l . body w e ig h t per in ta k e d ig e s tib ility d ig e s tib ility s im ila r d iffe re n c e s . w as ( B W /d ), In h ig h e r, W a g n e r 's 65% in s tu d y (1 9 8 6 ) d i d n o t d u rin g v itro 1983 o rg a n ic fo ra g e m a tte r (IVOMD), t h a n t h a t r e p o r t e d by K ro n b e rg i n 1982 (5 0 % ). c o m p a ris o n m e n tio n e d m uch day (3S1H) (1 9 8 6 ) t h e f o ll o w i n g y e a r , 1 9 8 3 , u s in g t h e same b i o l o g i c a l t y p e s and r a n g e l a n d a s K ro n b e rg e t a l . d e te c t la c ta tin g o f fiv e p re v io u s ly b io lo g ic a l was made by t y p e s on t h e W agner et a l. sam e r a n g e l a n d (1 9 8 6 ) A as d u r in g 1984. B i o l o g i c a l t y p e s u s e d i n t h i s s tu d y i n c l u d e HH, Angus X H e r e fo r d (A H ), 1 /4 S im m en tal X 3 / 4 (1 S 3 H ), H e r e fo r d S im m e n ta l X H e r e f o r d (SH) and 3S1H 16 la c ta tin g 2 .3 , co w s. 2 .5 , 61%. Mean f o r a g e i n t a k e f o r HHt AH, ISgH t SH and 3S1H was 2 .2 , 2 .6 , 2.8% M ilk p r o d u c t i o n cow s when m ilk o f BWZdt a c c o u n te d p ro d u c tio n , re s p e c tiv e ly , f o r 60% o f t h e when IVOMD a v e ra g e d v a ria tio n w e ig h t:h e ig h t r a t i o s among t h e s e and body w e ig h t w e re u s e d a s c o v a r i a t e s i n a r e g r e s s i o n m o d e l. R e tic u lo ru m e n Volume A lo n g h y p e r tr o p h y w ith d u r in g re tic u lo ru m e n S h o r th o r n an in c re a s e in la c ta tio n , v o lu m e . m onozygous volum e w ith l a c t a t i o n . th e re T u llo h tw in s re tic u lo ru m e n to is an ( 19 6 6 a ) assess a s s o c ia te d u sed d iffe re n c e s g re a te r m id d ig e s ts , fo r a ir fille d la c ta tin g co w s. la c ta tio n la c ta tio n . w ith s m a lle r A ir f i l l e d by in c re a s e in and in Je rse y X re tic u lo ru m e n c a p a c i ti e s o f th e re tic u lo ru m e n f o r e a ch l a c t a t i n g a n d n o n l a c t a t i n g tw in w e re o b t a i n e d . d ry Je rse y cau sed The w e ig h t o f t h e d i g e s t s i n t h e r e t i c u l o r u m e n , and t h e w a t e r an d a i r f i l l e d and w e ig h t c a p a c ity and w a t e r f i l l e d The g r e a t e s t d iffe re n c e s e s tim a tio n s . ( U l y a t t and B a r t o n , 1 9 6 4 ). d iffe re n c e fo u n d c a p a c itie s re s u lte d d id th e w a te r f i l l e d W e ig h ts o f b o th t h e w e t d u r in g c a p a c ity o c c u rre d e a rly i n much t h e w ere d u r in g an d la te same t r e n d s a s S i m i l a r r e s u l t s w e re fo u n d i n s h e e p T u llo h (1 9 6 6 b ) a ls o fo u n d t h e l e n g t h and i n t e r n a l c ir c u m f e r e n c e o f t h e i n t e s t i n a l la m in a o f t h e s m a ll and l a r g e i n t e s t i n e t o b e l a r g e r f o r l a c t a t i n g a n im a ls . Work by C am pbell and F e l l ( 1964) fo u n d h y p e r tr o p h y o f t h e GI t r a c t c o u ld be p re v e n te d in ra ts am o u n ts a s n o n l a c t a t i n g r a t s . if la c ta tin g a n im a ls w e re fe d th e same T h is s u g g e s t s i n t a k e may b e a c a u s e o f 17 . h y p e rtro p h y . However M owatt (1 9 7 3 ; a s c i t e d d iffe re n c e in p re c a lv in g and fo o d re tic u lo ru m e n in ta k e . at w a te r p a rtu ritio n fille d w ith o u t by F o r b e s , 1986 ) fo u n d a c a p a c ity a b e tw e e n c o r r e s p o n d in g T h is w o u ld s u g g e s t o t h e r i n f l u e n c e s , tw o w eeks d iffe re n c e in i n c l u d i n g h o rm o n a l c o n t r o l , may a f f e c t h y p e r tr o p h y and r e t i c u l o r u m e n v o lu m e . R e tic u lo ru m e n v o lu m e s h o u ld a ls o be a v a i l a b l e s p a c e i n t h e a b d o m in a l c a v i t y . lim ite d by th e am ount of ( I 98 O) e s t i m a t e d N u tt e t . a l . r u m in a l volum e w ith e x t e r n a l m a r k e rs o f Angus cows w ith v a r y i n g fra m e s iz e s . A p o s itiv e re la tio n s h ip w as fo u n d b e tw e e n r u m in a l volum e and fra m e s i z e . I n a d d i t i o n cow s g r a z i n g lo w e r q u a l i t y p a s t u r e s h ad l a r g e r rum ens w i t h in c re a s e d in ta k e . T h is re la tio n s h ip w as n o t fo u n d w ith a n im a ls g r a z i n g h ig h q u a l i t y p a s t u r e s . F a t ig u e When th e e n e rg y e x p e n d itu re s of s e e k in g fo o d , h a r v e s t becom e g r e a t e r t h a n t h e e n e rg y consum ed i t a n im a l w i l l s u f f e ,r f a t i g u e or e x h a u s tio n . T h e se and g ra z in g re sp o n se s tim e a re ( A r n o ld . a p p a re n tly a lik e ly th a t and th e As t h e q u a n t i t y o f . f o r a g e l e s s e n s t h e r e i s a g e n e r a l i n c r e a s e i n b o th b i t e 1976) is p re h e n s io n ra te I9 6 0 ; S c a r n e c c h ia m eans of (C hacon e t a l . , et s u s ta in in g a l., in ta k e 1985) • le v e ls s i n c e a n im a ls a r e a b l e t o m a i n ta i n i n t a k e l e v e l s w i t h d e c l i n i n g f o r a g e a v a ila b ility a ttrib u te d ( H a v s ta d to et fa tig u e a l., 1 9 8 3 ). a p p e ars to H ow ever, occur when a d e c lin e g ra z in g a p p r o x im a te ly 1 0 .8 h ( S c a r n e c c h i a e t a l . , 1985) t o in tim e in ta k e exceeds 1 2 .0 h o u r s ( S t o b b s , 18 1 9 7 5 ). to D i f f e r e n c e s i n t h e l e n g t h o f g r a z i n g tim e n e c e s s a r y f o r f a t i g u e occur i s lik e ly to d e p e n d upon a m u l t i p l i c i t y f o r a g e d e n s i t y , s t r u c t u r e and t e n s i l e s tre n g th . of fa c to rs , su c h a s 19 MATERIALS AND METHODS T h is r e s e a r c h p r o j e c t was c o n d u c te d d u r in g t h e sum m ers o f 1985 and 1986 i n c o o p e r a t i o n w ith t h e N o r th e r n A g r i c u l t u r a l E x p e rim e n t S t a t i o n l o c a t e d n e a r H a v re , M o n tan a. A lth o u g h t h e r e s e a r c h o b j e c t i v e s f o r b o th y e a r s w e re t h e sam e, t e c h n i q u e s w e re m o d if ie d i n a c cu ra cy of in fe re n c e s d e riv e d fro m th e 1986 t o i n c r e a s e t h e d a ta . B ecause of th e s e c h a n g e s , e a c h y e a r w i l l be t r e a t e d s e p a r a t e l y i n t h i s an d t h e f o l l o w i n g s e c tio n . M eth o d o lo g y Used I n 1985 D u rin g from each N o rth e rn 1985 of s ix ' p reg n a n t fiv e b io lo g ic a l A g ric u ltu ra l ty p e s in c lu d e d in t h i s H e re fo rd (A H ), and l a c t a t i n g 1 /4 ty p e s R e s e a rc h w e re C e n t e r 's a n im a ls , ran d o m ly c ro ssb re d h e rd . s tu d y w e re : s t r a i g h t b r e d H e r e f o r d S im m e n ta l X 3 /4 H e re fo rd by e i t h e r H av re L in e 4 , P o l le d 9 y r o ld , s e le c te d (1 S 3 H ), H e r e fo r d (SH) and 3 /4 S im m en tal X I / 4 H e r e fo r d (3 S 1 H ). s ire d 6 to fro m th e B io lo g ic a l (H H ), Angus X S im m en tal X A ll c a l v e s w e re o r h o rn e d H e r e f o r d b u l l s . T h ese b i o l o g i c a l t y p e s w ere s e l e c t e d t o r e p r e s e n t d i f f e r e n c e s i n m a tu re s i z e and m ilk p ro d u c tio n (ta b le I). W ith in th e s e b io lo g ic a l ty p e s th e i n c r e a s i n g S im m e n ta l i n f l u e n c e r e p r e s e n t e d a b e e f cow t y p e w ith h i g h e r m ilk p r o d u c t i o n a n d l a r g e r body s i z e . re p re s e n te d a p ro d u c tio n . M anagem ent o f t h e h e r d w as d e s ig n e d t o m anagem ent s m a lle r p r a c tic e s b io lo g ic a l The Angus an d H e r e f o r d i n f l u e n c e commonly u se d cow by ty p e c o w -c a lf w ith m o d e ra te re p lic a te p ro d u ce rs in m ilk ty p ic a l N o rth 20 C e n tra l M o n tan a. The o v e ra ll goal of th e p ro je c t w as to m easu re â– • ' â– â– m a t e r n a l c h a r a c t e r i s t i c s o f e a c h b i o l o g i c a l ty p e o v e r a 10 y e a r p e r i o d ( K r e s s e t a l . , 1 9 8 6 ). T a b le I . T r a i t s o f b e e f cow b i o l o g i c a l t y p e s , 1985ab Body S i z e M ilk P r o d u c ti o n Cow Type HH + ++ AH ++ ++ I S3 H ++ ++ SH +++ +++ 3 SI H ++++ ++++ a A d a p te d fro m K r e s s e t a l . ( 1 9 8 6 ) . bMore + ' s = g r e a t e r m ilk p r o d u c t i o n o r body w e i g h t. The s tu d y s i t e w as l o c a t e d i n t h e B earpaw M o u n ta in s a p p r o x im a te ly 32 km s o u t h e a s t o f H a v re , M o n tan a. was 81 h a i n s i z e The p a s t u r e u s e d d u r in g t h e s tu d y w ith s l o p e s up t o 40%. E l e v a t i o n o f t h e s tu d y s i t e a v e r a g e s 1300 m w ith a n n u a l p r e c i p i t a t i o n r a n g i n g fro m 4 5 .7 t o 5 0 .8 cm. The s i t e s ilty is c la s s ifie d ran g e g la c ia te d s ite p la in s . o f ro u g h f e s c u e and p in e of by th e th e S o il C o n s e r v a tio n S e rv ic e (1 9 7 6 ) F o re s t-G ra s s la n d c o m p lex in D om inant v e g e t a t i o n on th e s te e p e r s lo p e s (F e s t u c a s c a b r e l l a ) , Id a h o f e s c u e b lu e b u n c h w h e a t g r a s s ( A g ro p y ro n th e s p ic a t u m ) w ith (P in u s p o n d e r o s a ) o v e r s t o r y i n l o c a l i z e d a r e a s . ty p ic a l of fo o th ill b u n c h g ra ss ra n g e la n d in a w e s te rn c o n s is ts (F e s t u c a i d a h o e n s i s ) an op en p o n d e ro s a The m ore g r a d u a l s l o p e s w e re d o m in a te d by K e n tu c k y b l u e g r a s s ( Poa p r a t e n s i s ) . is as M o n tan a. The a r e a The s tu d y 21 a n im a ls w e re moved t o t h i s p a s t u r e J u l y 2 0 , and w e re moved t o a s i m i l a r , a d j a c e n t p a s t u r e on A u g u st 2 9 . The s t o c k i n g r a t e d u r in g t h e s tu d y w as 1 .2 ha/AUM. M ilk p r o d u c t i o n w as e s t i m a t e d on A u g u st 2 and A u g u st 21 u s in g t h e w e ig h - s u c k le - w e ig h t e c h n i q u e d e s c r i b e d by W illia m s ( 1 9 7 9 ) . and h i p h e ig h ts O c to b e r 1 . ( w t:h t) o b ta in e d a fte r a 12 h s h r i n k d u r i n g w e a n in g on Body c o n d i t i o n s c o r e s w e re e s ti m a t e d b a s e d on w e i g h t : h e i g h t ra tio s . b e tw e e n h t : w t d iffe rin g w ere Cow w e i g h ts K lo s te rm a n e t a l . m e a s u re m e n ts and b io lo g ic a l ty p e s . (1 9 6 8 ) r e p o r t e d a h ig h c o r r e l a t i o n body c o n d itio n among m a tu re cows o f A d d i t i o n a l body w e ig h t m e a s u re m e n ts w e re o b t a i n e d a t p r e - and p o s t b r e e d i n g , an d a t e a c h m ilk t e s t . F o ra g e o r g a n i c m a t t e r i n t a k e (OMI) was e s t i m a t e d fro m b o th d a i l y f e c a l o r g a n i c m a t t e r o u t p u t (FOMO) and f o r a g e IVOMD u s i n g t h e e q u a t i o n : OMI = FOMO / ( I -IVOMD) . D u rin g t h e firs t f e c a l o u t p u t w as e s t i m a t e d u s in g b o th t o t a l 3S1H cow s) and a C r2 Og d i l u t i o n te c h n iq u e and t h i r d w eeks o f A u g u st fe c a l c o lle c tio n s (R a le ig h , 1980; (RH an d a ll c o w s). T o t a l f e c a l c o l l e c t i o n s w e re e s t i m a t e d u s in g f e c a l c o l l e c t i o n b a g s and u r i n e s e p a r a t i o n f l a p s ( K a r tc h n e r and C a m p b e ll, 1 9 7 9 )• F iv e d a y s p r i o r t o , and d u r in g t o t a l f e c a l c o l l e c t i o n s a l l cows w ere b o lu s e d w i t h 10 gm o f pow dered C r2 Og i n a g e l a t i n c a p s u l e e a c h e v e n in g a t 1800 h . fo u r days o f t o t a l fec a l c o lle c tio n s ,, c o lle c tio n On t h e b a g s w e re ch a n g ed a t 600 arid 1800 h . F e c e s c o l l e c t i o n s w e re w e ig h e d , sa m p le d a n d f r o z e n f o r la te r d e te rm in a tio n (AOAC, I 9 6 0 ) . to 1900 c o n te n t. h and of d ry m a tte r, o rg a n ic m a tte r and C r 2 O3 c o n t e n t R e c t a l g r a b s a m p le s from a l l cows w e re c o l l e c t e d a t 1800 w e re a ls o fro z e n u n til la b o ra to ry a n a ly s is fo r C r 2 O3 Chromium c o n t e n t o f t h e g r a b s a m p le s w as e s t i m a t e d by u s e o f 22 a to m ic a b s o rb tio n W illia m s e t le s s a l. s p e c tro m e try (1 9 6 2 ). th a n 2mm w ith p re p a ra tio n fo r u s in g th e p ro ce d u re S am p les w e re thaw ed a t 4 0 °C , a W iley m i l l a to m ic b e fo r e a c id a b s o rb tio n s p e c tro m e try . d u r in g each fec a l c o lle c tio n w e re f r o z e n and l a t e r f r e e z e d rie d by and g ro u n d t o d ig e s tio n c o l l e c t i o n s u s in g e i g h t e s o p h a g e a l I y f i s t u l a t e d c o lle c te d d e s c rib e d of s a m p le s i n Two f o r a g e e x tru s a (RH and 3S1H) cows w ere p e rio d . E x tru s a c o lle c tio n s and g ro u n d th r o u g h a Imm s i e v e fo r IVOMD e s t i m a t i o n u s in g t h e B a r n e s m o d i f i c a t i o n o f t h e T i l l e y and T e r r y te c h n iq u e (H a rris , c a n n u la te d v a lu e of 1 9 7 0 ). cow s f e d Rumen ad l i b i t u m 55% IVOMD was used flu id was o b t a i n e d g ra ss hay. as a A g rass s ta n d a rd and fro m two h ay w ith a ll rum en a known s a m p le s w ere s h ip p e d to r e p lic a te d th r e e tim e s . D u rin g th e p a c k in g p la n t s p le e n , lu n g s, firs t in week B u tte , k id n e y s in Novem ber M o n tan a, and k id n e y a ll cows w e re w h e re w e i g h ts of th e f a t w e re o b t a i n e d . liv e r, a h e a rt, R e tic u lo r u m e n s w e re rem o v e d , e m p tie d and s t o r e d i n w a t e r u n t i l t h e f o l l o w i n g day when e x c e s s f a t w as rem oved fro m t h e s u r f a c e . s e c u re ly th e s titc h e d re tic u lo ru m e n . w a t e r and f i l l e d p ressu re c lo s e d and th e The o p e n in g t o t h e omasum w as eso p h ag u s t ie d o ff E ach r e t i c u l o r u m e n was e m e rse d i n w i t h w a te r a t a c o n s ta n t o f 4 cm o f w a t e r was a c h i e v e d . p ressu re R e tic u lo ru m e n d r a i n e d fro m t h e t i s s u e . w e ig h ts w e re m e a su re d th e th e a fte r c a rd ia of a ta n k o f warm u n til The p o t e n t i a l volum e w as t h e n r e a d a s t h e c h a n g e o f t h e w a t e r i n 19 6 6 a ). at a in te rn a l re tic u lo ru m e n ta n k th e (T u llo h , w a te r had 23 M e th o d o lg y Used I n 1986 S ix ty p e s p re g n a n t, w ere used r a n d o m ly la c ta tin g as s tu d y s e le c te d c ro ssb re d fro m h e rd . S tra ig h tb re d 3 yr a n im a ls th e cows e a c h d u r in g N o r th e r n B io lo g ic a l H e re fo rd o ld 1986. of T h e se A g ric u ltu ra l ty p e s in c lu d e d (H H ), T a r e n t a i s e fo u r a n im a ls R e s e a rc h in X H e re fo rd b io lo g ic a l th e w e re C e n te r’ s s tu d y w ere: (T H ), T a r e n t a i s e X ( S im m en tal X H e r e f o r d ) (T (S H )) and C h a r o l a i s X ( S im m e n ta l X H e r e f o r d ) (C (S H )). T(SH) W ith in th e g ro u p th re e w ere 50% T a r e n t a i s e - 25% S im m e n ta l - 25% H e r e f o r d w ith t h e r e m a in in g t h r e e b e in g 50% T a r e n t a i s e - 37.5% S im m en tal - 12.5% H e r e f o r d . The C(SH) g r o u p w as a l s o d i v i d e d s i m i l a r l y w i t h t h r e e a n im a ls b e in g 50% C h a r o l a i s - 25% S im m e n ta l - 25% H e re fo rd and H e re fo rd . th re e T h e se b e in g a d d itio n a l 50% C h a r o l a i s s ire b ree d s - 37.5% S im m en tal re p re s e n te d - 12.5% b io lo g ic a l ty p e s w ith medium body s i z e , h ig h m ilk p r o d u c t i o n ( T a r e n t a i s e ) an d l a r g e body s iz e w i t h m o d e r a te m ilk p ro d u c tio n ( C h a r o la i s ; b r e d t o b u l l s o f t h e same b r e e d s a s i n 1 9 8 5 . T a b le 2 ). Cows w e re H erd m anagem ent w as a l s o s i m i l a r d u r in g 1986 t o t h a t em ployed i n . 1985. The s tu d y a n im a ls w e re p a s t u r e d in t h e p a s t u r e u s e d i n t h e 1985 s tu d y . s iz e • th e y e a rs. • O c to b e r to p o g ra p h y F ifty -s ix I, M ilk e s tim a te d w ith and v e g e t a t i o n a 276 h a p a s t u r e a d j a c e n t t o W ith t h e e x c e p t i o n o f t h e p a s t u r e com plex w e re v e r y cow s w ere p r e s e n t on th e th e s to c k in g r a t e p ro d u c tio n u s in g 30 d a y s p o s t w e a n in g on S e p te m b e r 3 0 , th e c a lv in g , 1 9 86. fo r th e s tu d y s i t e p e rio d fro m J u l y 22 t o b e in g w e ig h -s u c k le -w e ig h J u ly s i m i l a r b e tw e e n 1 .2 h a / AUM. te c h n iq u e w as 1 8 , A ugust 22 and j u s t p r i o r t o Cow w e i g h ts a f t e r a 10 h s h r i n k w ere 24 o b ta in e d d u r in g th e la s t m ilk p ro d u c tio n te s t. H ip h e ig h ts w e re m e a su re d a t w e a n in g on O c to b e r I . O rg a n ic m a t t e r i n t a k e was e s t i m a t e d w ith on a l l cows d u r in g t h e l a s t week i n J u l y , S e p te m b e r. to ta l fe c a l c o lle c tio n s and d u r in g t h e l a s t week i n T h re e e s o p h a g e a l f i s t u l a c o l l e c t i o n s w e re made t h r e e t im e s d u r in g e a c h f e c a l c o l l e c t i o n p e r i o d u s in g f o u r HH a n i m a l s . to In a d d itio n IVOMD a n a l y s i s o f e x t r u s a , a n a l y s e s o f a c id d e t e r g e n t f i b e r , p ro te in and a c id d e te rg e n t lig n in ( AOAC, 1980) w ere c ru d e c o m p l e te d as a d d itio n a l in d ic a to r s o f fo ra g e q u a li ty . A ll a n im a ls w ere s h ip p e d t o B u t t e , M o n tan a, and v i t a l d a ta w e re o b ta in e d on O c to b e r r e t i c u l o r u m e n vo lu m e w as m e a s u re d . 9 and 10. T he o rg a n m ass f o llo w in g day M easu rem en ts o f b a c k f a t a t t h e 1 2 ^ r i b i n t e r f a c e and m a r b lin g s c o r e s o f t h e l o n g is s im u s m u sc le u s in g USDA (1 9 7 5 ) s t a n d a r d s w e re made t o f u r t h e r e s t i m a t e body f a t c o n t e n t . S t a t i s t i c a l A n a l y s is The d a t a c o m p le te c o n c e r n in g v i s c e r a l b lo c k d e s ig n . m ass w ere a n a ly z e d M e asu re d tra its at a n a ly s is te s t ty p e s w ith in o f v a ria n c e fo r mean S ta tis tic a l p ro ce d u re . a year w as w ith a p r o t e c t e d s e p a ra tio n . A n a ly s is R e g r e s s io n S y s t e m 's . (S A S , a n a ly z e d le a s t a n a ly s e s w ith in D iffe re n c e s u s in g sq u a re s 1985) a ra n d o m iz e d s la u g h te r b i o l o g i c a l ty p e w e re a n a ly z e d a s ra n d o m iz e d b l o c k . b io lo g ic a l as le a s t com puted s te p w is e among sq u a re s d iffe re n c e w e re a (LSD) u s in g regression 25 L i n e a r r e g r e s s i o n m o d e ls w i t h m i l k p r o d u c t i o n a n d o r g a n i c m a t t e r in ta k e c lo se st b io lo g ic a l to type w e a n in g a s as a m ain dependent effect v a ria b le s w e re when one way a n a l y s i s d e t e r m i n e d s i g n i f i c a n t d i f f e r e n c e s among b i o l o g i c a l m o d els u sin g b io lo g ic a l age of th e same dependent v a ria b le s t y p e a s a m ain e f f e c t . c a lf, c a lf p re c e d in g w ean in g , w eig h t at w e re c a lf w ean in g , R e g ressio n c a lc u la te d average w ith o f v arian ce ty p e s. G o v a ria te s in c lu d e d : w ean in g , cow w e i g h t a t com puted w ith o u t sex of c a l f , d a ily g a in (ADG) cow ADG p r e c e d i n g w e a n i n g , cow h e i g h t , cow c o n d i t i o n a t w e a n i n g , s p l e e n w e i g h t , h e a r t w e i g h t , l u n g w e ig h t, l i v e r w e ig h t, w e ig h t, to ta l kidney w e ig h t, organ w e ig h t, k id n ey f a t w e ig h t, h o t c a rc a s s w e ig h t, reticu lo ru m e n r e t i c u l o r u m e n v o lu m e , m i l k p r o d u c t i o n and o r g a n i c m a t t e r i n t a k e a t w e a n in g . To i d e n t i f y th e f a c t o r s in f l u e n c i n g fo ra g e in ta k e d u rin g a stu d y y e a r d a t a w e re a l s o a n a l y z e d w i t h a c o m p l e te r a n d o m iz e d b l o c k d e s i g n . In d ep en d en t v a ria b le s m e a s u r e m e n t, a c a lf, and c a lf in c lu d e d : b io lo g ic a l age. type E rror b io lo g ic a l X d a te term of in clu d e d ty p e , in ta k e d a te of in te ra c tio n , cow w i t h i n breed. r e s u l t s a r e r e p o r t e d s e p a r a t e l y i n a p p e n d i x T a b l e s 24 and 2 5 . in ta k e sex of T h e se 26 RESULTS 1985 T h e r e w e re no d i f f e r e n c e s ( P X I O ) i n t h e s h r u n k body w e i g h t s among th e fiv e b io lo g ic a l ty p es (T a b le 2 ) . How ever, t h e r e w ere d i f f e r e n c e s ( P C .10) i n t h e h o t c a r c a s s w e i g h t s , w i t h t h e AH g r o u p h a v i n g a h e a v i e r carcass. The HH and 3S1H ha d t h e l o w e s t c a r c a s s w e i g h t s w i t h t h e 1S3H an d SH cows b e i n g s i m i l a r t o e i t h e r e x t r e m e . Hip h e i g h t s w e re a l s o s i m i l a r ( P X 1 0 ) a c r o s s a l l b i o l o g i c a l t y p e s . Body c o n d i t i o n w ith th e and k i d n e y rem a in in g fat b io lo g ic a l w e i g h t s w e re l o w e s t ty p e s h a v in g for e q u a b le t h e 3S1H g r o u p c o n d itio n sco res. K id n ey f a t w e i g h t was a l s o l o w e s t ( P C .05) f o r t h e 3S1H cows and h i g h e s t f o r t h e AH, HH and I S 3 H .a n im a ls ( T a b l e 2 ) . T ab le 2. B io lo g ic a l ty p e Body w e i g h t , body c o n d i t i o n , h i p h e i g h t , k i d n e y f a t w e i g h t an d h o t c a r c a s s w e i g h t o f f i v e d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s , 1985a Body Weight kfc Body C o n d itio n w t:h t Hip H eight cm Kidney F at kg Hot C arcass kg 588.24 + 17.6 5.75 + 0 .1 7 b 131.0 + 1 .73 CO +1 O HH AH 605.93 + 14.5 6.3 3 + 0 .3 1 b 131.2 + 1 .28 3 .6 3 + 0 .5 2 d 1S3H 588.47 + 17-1 5.92 + 0 . l 6 b 132.5 + I .89 2 .44 + 0 .2 2 e f 2 8 0 .2 5 + 6 .1 7 b° SH 615.91 + 14.2 5 .7 5 + 0 .1 7 b 134.7 + 1 .2 6 2.31 + 0 .1 5 e f 288.26 + 7 .5 3 bc 3S1H 597.39 + 14.7 5.0 8 + 0 .3 8 ° 134.8 + 0 .7 0 2.14 + 0 .2 9 f 0 .1 7 de 276.24 + 8 .07° a L ea st sq u a re means +. SE. bc Means w ith in ' a column w ith d i f f e r e n t s u p e r s c r i p t d i f f e r (P < .1 0 ) . d e f Means w ith in a column w ith d i f f e r e n t s u p e r s c r i p t d i f f e r ( P < .0 5 ) . 3 0 0 .4 3 + 8 .93b 2 69.14 + 8.37° 27 M ilk p r o d u c t i o n d i d n o t v a r y ( P X I O ) among b i o l o g i c a l t y p e s ( T a b l e 3). th e How ever, t h e r e t e n d e d t o second m ilk p ro d u ctio n be a i n c r e a s e i n m ilk p ro d u c tio n d u r in g te st over th e first te st. The r a t i o of h e i f e r s t o s t e e r c a l v e s was 1 : 1 , 2 : 1 , 2; I and 2:1 f o r HH, AH, 1S3H and SH c o w s, o n ly re sp e c tiv e ly . The 3S1H g r o u p Mean c a l f a g e s a t w e a n in g w e re 16 8 , AH, 1S3H , SH a n d 3S1H cow s, su c k le d 1 78, 1 8 6 , 177 and re s p e c tiv e ly .. B irth h e ife r c a lv e s. 177 d a y s f o r HH, w e ig h ts for a ll b i o l o g i c a l t y p e s a p p r o x i m a t e d 40 k g , and mean v a l u e s f o r 205 d w e a n in g w e i g h t w e re s i m i l a r (2 6 0 k g ) f o r a l l b i o l o g i c a l t y p e s e x c e p t f o r t h e SH g r o u p (317 k g ) . 4. F a c to rs C alf average d a il y g a in s in c lu d in g c a lf sex, c a lf age, (ADG) a r e r e p o r t e d b irth in T ab le w e ig h t and c a l f h a v e b e e n r e p o r t e d t o i n f l u e n c e m i l k p r o d u c t i o n ( C a s e b o l t , 1984).. T able 3. D a te 8 /2 /8 5 8 /2 9 /8 5 Mean HH 8 .7 3 + 0 .7 6 8 .7 9 + 0 .8 6 8 .7 6 + 0 .2 7 AH 8 .7 1 +_ 1 . 16 1 0 .3 0 + 1 .0 2 9 .51 + o .96 1S3H 7 . 6 2 + 1 .3 8 1 0 .3 0 + 0 .7 5 8 .9 6 + 0 .8 2 SH 8.9 1 I+ O VO Cr. B io lo g ic a l ty p e A v e ra g e d a i l y m i l k p r o d u c t i o n ( k g / d ) f o r f i v e b e e f cow b i o l o g i c a l t y p e s , 1985ab 11.71 + 1 .3 7 10.21 + 0 . 1 8 3S1H 9 . 9 8 +_ 0 .7 1 1 1 .8 5 + 0 .8 6 1 0 .9 2 + 0 .5 7 a L e a s t s q u a r e m eans + SE. bP > . 1 . age 28 T able 4. C a l f a v e r a g e d a i l y g a i n (k g ) from dams o f f i v e d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s , I 985a P e r i o d ___________________________ B io lo g ic a l type 6 /3 - 7 /2 2 7/22 - 8/2 8 / 2 - 8 /2 9 . 8 /2 9 - 10/1 HH .8 8 + .0 5 I .0 8 + .0 6 b 1.03 .02 1 .1 5 + .0 2 AH . 9 8 + .0 4 1 .06 + .0 7 b 1 .1 5 + .0 5 1 .1 0 + .05 1S3H .88 1 .17 + .0 4 bc 1 .1 2 + .04 1 .1 5 + .03 SH .97 + . 0 5 v I .2 8 + .0 7 ° 1 .1 9 + .06 1 .2 9 + .1 0 3S1H .8 6 + .0 4 1 .17 + .0 9 bc 1 .1 2 + .04 I .1 2 + .07 + .11 + a L e a s t s q u a r e m eans +. SE. b c Means w i t h i n a colum n w i t h d i f f e r e n t s u p e r s c r i p t d i f f e r (P < .1 0 ). Of th e re g re ssio n m o d els fo r m ilk b i o l o g i c a l t y p e a s a m ain e f f e c t was n o t p ro d u ctio n sig n ific a n t th e model (P > .1 0 ). w ith In th e m odel w i t h o u t b i o l o g i c a l t y p e a s a m ain e f f e c t t h e w e i g h t o f t h e l u n g s , k i d n e y f a t and r e t i c u l o r u m e n a c c o u n t e d f o r 38% o f t h e v a r i a t i o n i n m i l k p r o d u c t i o n a t w e a n in g ( T a b l e 5 ) . A ve ra g e d a i l y not d iffe re n t g a i n s d u r i n g mid and l a t e la c ta tio n ( T a b l e 6) w e re ( P > .1 0 ) among b i o l o g i c a l t y p e s w i t h i n a p e r i o d , y e t g a i n s a c r o s s p e r i o d s w e re d i f f e r e n t . D u r i n g J u n e and t h e f i r s t two t h i r d s o f J u l y a l l cows g a i n e d a n a v e r a g e o f 0 . 6 6 k g a d a y . days g a in in c re a s e d to a n im a ls d e c re a s e d to In th e fo llo w in g 10 1 .0 5 k g a d a y . A verage d a i l y g a i n f o r t h e s t u d y -0 .2 6 k g /d d u r in g A ugust, r e l a t i v e l y c o n s ta n t th ro u g h Sep tem b er. w ith w eig h t rem a in in g 29 T able 5. S te p w ise r e g r e s s i o n c o e f f i c i e n t s f o r m ilk p ro d u c tio n p r i o r t o w e a n i n g , 1985 V a ria b le Bo K id n e y f a t w e i g h t Lung w e i g h t R e tic u lo ru m e n w e ig h t B1 1 1 .2 1 4 5 1 1 .4 0 9 0 '1 2 . 7 3 0 9 - 1 .1521** - 0 .9 5 7 6 * 0 .3 6 4 3 MSE 4 .4 5 6 9 R2 0 .3 8 0 5 “ ” * * P C .10 . â– * P C .05 * e ”PC.01 T able 6 . B io lo g ic a l type A v e ra g e d a i l y g a i n (k g ) f o r f i v e d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s , 1985ab ______________ ;___________ P e r i o d 6 /3 - 7 /22 7 /22 8/2 8 / 2 - 8 /2 9 8 /2 9 - 10/1 .6 9 ± 0 . 6 0 - . 2 7 + 0 .2 1 - . 0 7 + 0 .1 1 AH .7 6 + 0 . 1 0 • 92 ± 0 .51 - .2 9 + 0 .1 2 —•01 + 0 . 1 9 1S3H .8 5 + 0 . 2 2 1 .4 2 + 0 . 5 2 - . 0 5 + 0 .4 5 .0 8 + 0 .1 3 SH .5 7 + 0 . 1 8 .91 + 1 .0 5 - . 2 4 + 0 .3 5 .26 + 0 .0 5 3S1H .4 7 + 0 . 1 1 - .4 4 + 0 .1 2 - . 1 5 + 0 .2 3 a L e a s t s q u a r e s m eans + SE. bP X I O . CO 1 .2 9 + .ro .6 4 + 0 .1 1 O HH 30 D a i l y OMI ( T a b l e 7) i n k g / d and a s a p e r c e n t o f body w e ig h t (%BW) d id not d i f f e r in in ta k e ( P > .1 0 ) among cow t y p e s . b e tw e e n th e two p e r i o d s T h e re was a n i n c r e a s e m e a s u re d for th e BH, cow s. IVOMD w as e s t i m a t e d a t 43% f o r b o t h i n t a k e p e r i o d s . T ab le 7. ( P < .1 0 ) AH and 1S3H O r g a n ic m a t t e r i n t a k e p e r da y (01'11/d, k g ) , and OMI/d a s p e r c e n t o f body w e i g h t (%BW) f o r f i v e b e e f cow b i o l o g i c a l t y p e s , 1985ab D a te B io lo g ic a l ty p e 8 /2 1 /8 5 - 8 /2 5 /8 5 OMI/d.*BW OMI/d 8 /8 /8 5 - 8 /1 1 /8 5 OMI/d.%BW OMI/d HH 6 .4 0 + .1 3 1.07 + .0 4 7 . 5 8 + .2 2 1 .2 8 + .0 5 AH 7 . 1 9 + .2 2 1 .1 7 + .0 2 7 .7 1 + .35 1 .2 7 + .0 5 1S3H 6 .9 1 + .2 2 I .1 5 + .0 3 7 . 8 3 + .2 4 1 .3 4 + .0 5 SH 7 . 9 0 + .3 0 1 .2 7 + .0 4 8 . 0 2 + .4 8 1 .2 9 + .07 3S1H 7 . 3 9 + .6 0 I .21 + .1 2 7 . 4 5 + .1 8 1 .2 4 + .03 a L e a s t s q u a r e m eans +_ SE. bP > .1 0 . A m odel w eaning, in clu d in g c a lf g a in sex o f p rio r to c a lf, age of c a lf, w e a n in g and sp le e n m ilk p r o d u c tio n a t w eig h t as co v a riate s a c c o u n t e d f o r 54% o f t h e v a r i a t i o n i n OMI p r i o r t o w e a n in g ( T a b le 8 ) . Of t h e v i t a l o r g a n s m e a s u re d o n l y t h e k i d n e y s and t h e l i v e r showed d iffe re n c es w ith th e ( P < .1 0 j T a b l e 9) • rem a in in g b io lo g ic a l The 3S1H g r o u p had t h e l a r g e s t k i d n e y s ty p e s B oth SH and 3S1H had l a r g e r l i v e r s h a v in g sim ila r k id n ey w e ig h ts. ( P < . 1 0) t h a n t h e HH and 1S3H, t h e AH g r o u p e x h i b i t e d i n t e r m e d i a t e l i v e r w e i g h t s . and .When o r g a n w e i g h t s 31 w ere e x p r e s s e d a s a p e r c e n t o f body w e i g h t ( T a b l e 10) t h e 3S1H cows had a h i g h e r p e r c e n t a g e o f t h e i r body w e i g h t a s k i d n e y w e i g h t t h a n o t h e r b i o lo g i c a l ty p e s (P < .1 0 ). The 3S1H g r o u p a l s o ha d t h e h i g h e s t l i v e r t o body w e i g h t p e r c e n t a g e , BH, AH, and 1S3H g r o u p s t h e l o w e s t , and t h e SH g r o u p was i n t e r m e d i a t e . R e t i c u l o r u m e n volum e d i d not d iffe r among b i o l o g i c a l t y p e s ( T a b l e 1 1 ) . T ab le 8. S tep w ise r e g r e s s i o n c o e f f i c i e n t s f o r o rg a n ic m a tte r i n t a k e p r i o r t o w e a n i n g , 1985 V a ria b le Bo Sex o f c a l f Age o f c a l f M ilk p r o d u c t i o n p r i o r t o w e a n in g C a l f ADG p r i o r t o w e a n in g S p le en w eig h t B1 7 .8 1 7 6 7 .3 3 8 4 0 .4 5 1 9 a " -0 .0 2 7 3 "* * 7 .2 6 2 5 9 .4 1 7 9 8 .9 1 0 0 -0 .1 0 3 2 °« 2 .0 5 2 2 « 1 .5 4 4 3 " MSE 0 .3 0 9 1 R2 0 .5 3 5 6 " » * a The c l a s s v a r i a b l e Sex i s s c o r e d : c a lf. * P C .1 0 . P C .0 5 . trteiiP C .0 1 . I= H e ife r c a l f , P = S teer (P X lO ) 32 T ab le 9. O rgan m ass o f f i v e d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s , 1985* B io lo g ic a l H eart Kidney Lung L iv e r ty p e Ycr S p leen R eticulorum en . 2.2 0 + .07 1.11 + .04b 5 .0 5 ± .IO b 4.31 + .66 0.71 + .05 12.95 + .74 AH 2 .2 0 ± .12 1.0 8 + .02b 5 .2 5 ± .08bc 3 .5 5 + .11 0.71 + .02 12.83 + .44 1S3H 2 .1 4 + .10 1.13 + .04b 5.11 ± .22° 3 .6 0 + .17 0.71 + .04 13-53 SH 2 .2 9 + .05 1.12 + .04b 5.56 + .16° 4 .0 3 + .25 0.8 6 + .08 14.90 + .82 3S1H CM + .08 1.3 0 + . 10° 5 .5 2 + .0 9 ° 3 .7 7 + .27 0.86 + .09 CM CO HH 15.08 + + .86 .73 a L e a st sq u a re means + .S E . bcMeans w ith in a column w ith d i f f e r e n t s u p e r s c r i p t d i f f e r ( P < .1 0 ) . T ab le 10. B io lo g ic a l ty p e Organ m ass a s a p e r c e n t o f body w e i g h t , o f f i v e d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s , 1985* H eart Kidney L iv e r Lung S p leen R eticulorum en HH 0.3 7 + .002 0 .1 9 + .008d 0.86 + .0 l6 b 0 .7 3 + .110 0 .1 2 + .004 2.21 + .122 AH 0.3 6 + .016 0 .1 8 + .OOltd 0.87 + .024b 0 .5 9 + .020 0 .1 2 + .004 2 .1 3 + .102 1S3H 0.36 + .012 0 .1 9 + .004d 0.87 + .0 l6 b 0.61 + .024 0 .1 2 + .004 2 .2 9 + .102 SH 0 .3 7 + i004 0 .1 8 + .OOltd 0.90 + .016bc 0 .6 6 + .045 0 .14 + .012 2 .4 2 + .139 3S1H 0 .3 9 + .008 0 .2 2 + .012® 0.93 + .016° 0 .6 3 + .040 0 .1 5 + .016 2 .53 + .110 a L e a st sq u a re means +_ SE. bcMeans w ith in a column w ith d i f f e r e n t s u p e r s c r i p t d i f f e r (P C .1 0 ). deMeans w ith in a column w ith d i f f e r e n t s u p e r s c r i p t d i f f e r ( P < .0 5 ) . 33 T a b l e 11. P o t e n t i a l r e t i c u l o r u m e n volum e o f f i v e d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s , 1985ab R e tic u lo ru m e n Volume ---------- I — -------- B io lo g ic a l type HH 5 8 .5 4 + 2 .3 0 AH 6 2 .2 9 + 7 .6 2 1S3H 6 3 .7 8 + 7 .2 2 SH 8 0 .3 2 + 1 0 .6 0 3S1H 6 8 .0 1 + 7 -1 3 a L e a s t s q u a r e m eans + SE. bP>.10. 1986 Body w e i g h t s f o r t h e RH, TH and T(SH) d i d n o t d i f f e r ( P X 1 0 ; T a b l e 1 2 ) , y e t t h e mean w e i g h t o f t h e C(SH) g r o u p was 9% l a r g e r t h e n e x t l a r g e s t g r o u p (HH). Hip h e i g h t s w e re a l s o t a l l e r ( P C .10) f o r t h e C(SH) g r o u p , w i t h t h e HH g r o u p b e i n g hot c a rc a s s w e ig h ts th e stu d y . ( P C .10) t h a n d id n o t d i f f e r M easurem ent o f : body f a t th e (P X 10) s h o rte st. In c o n tra st, among b i o l o g i c a l and body c o n d i t i o n d id ty p e s in not y ield a n y d i f f e r e n c e s ( P X 1 0 ) among b i o l o g i c a l t y p e s ( T a b l e 13) • M ilk group p ro d u ctio n d u rin g th e (T ab le firs t 14) th irty was days g rea test of ( P C .10) la c ta tio n . for The th e T (S H ) HH a n i m a l s e x h i b i t e d t h e l o w e s t v a l u e s ( P C . 10) f o r t h e s e c o n d m i l k p r o d u c t i o n t e s t on J u l y 18 . D i f f e r e n c e s i n m i l k p r o d u c t i o n w e re d i m i n i s h e d ( P X 1 0 ) 34 T a b l e 12. B io lo g ic a l type Body w e i g h t , body c o n d i t i o n , h i p h e i g h t and h o t c a r c a s s w e i g h t o f f o u r d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s , 1986a Hot C arcass kg Hip H eight cm Body C o n d itio n w t:h t Body Weight kg HH 516.95 + 3 .6 b 4 .0 5 + 0 .0 3 127.3 + 0 .8 8 d 233.25 + 2 .84 TH 515.51 + 1 7 .6b 3.90 + 0.0 9 132.0 + I .9 0 ° 244.04 + 9.46 T(SH) 507.58 + 4 .8 b 3.83 + 0.04 132.7 + 1 .14° 230.88 + 5 .2 9 C(SH) 561.18 + 2 3 .8 ° 4.07 + 0.1 3 137.5 + 1 .6 7 f 255.30 + 10.63 a L e a st sq u a re means and SE. bc Means w ith in a column w ith d i f f e r e n t 's u p e r s c r i p t d i f f e r (P < .1 0 ). d e tMeans w ith in a column w ith d i f f e r e n t s u p e r s c r i p t d i f f e r (PC .0 5 ) . T a b l e 13. K id n ey f a t w e i g h t , back f a t t h i c k n e s s and M a r b l in g s c o r e o f f o u r d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s , 1986ab M a r b l in g sco re K id n ey Fat kg Back Fat mm HH 2 .2 3 . + 0 . 2 4 1 .5 0 + 0 .4 1 .8 + 0 . 1 8 TH 2 .5 7 + 0 . 4 2 1 .7 5 + 0 . 5 1 .5 + 0 . 2 2 T(SH) 1.71 + 0 . 1 6 0 .6 7 + 0 . 2 1 .3 + 0 . 5 2 C(SH) 2 .1 8 + 0 .2 5 I .0 0 + 0 . 2 1 .5 + 0 . 2 2 B io lo g ic a l ty p e a L e a s t s q u a r e m eans +. SE. bP > . 1 0 . 35 f o r th e t e s t h ig h er d u r in g A ugust 22. ( P < .1 0 ) for T(SH) and M ilk p r o d u c t i o n lo w est ( P < . 1 0) h e i f e r c a l v e s t o s t e e r c a l v e s w ere 2 : 1 , T(SH) and C(SH) g r o u p s r e s p e c t i v e l y . a ll b io lo g ic a l group ty p e ty p es (35 k g ) . w ere 190, 174 of th e R a tio s and 2:1 of f o r HE, TH, w ith th e e x c e p tio n o f th e TH c a l v e s a t w e a n in g by b i o l o g i c a l days for HH, TH, T(SH) and C(SH ) I n a d d i t i o n , 205 day w e a n in g w e i g h t s w e re 2 0 5 , 2 2 4 , 252 and 241 k g f o r BH, TH, T(SH) g a in 183 C (S H ). 1 :1 , 0 .5 :1 n e a r 40 k g , and for w e a n in g was a g a i n B ir th w e ig h ts o f th e c a lv e s f o r The a v e r a g e age o f ' t h e 1 74, re sp e c tiv e ly . w ere at c a lv e s are and C (S H ), r e s p e c t i v e l y . liste d on T ab le 15 for four A verage d a i l y p e rio d s from p a r t u r i t i o n t o w e a n in g . T ab le 14. B io lo g ic a l ty p e A v e ra g e d a i l y m il k p r o d u c t i o n b i o l o g i c a l t y p e s , 1986a (k g /d ) f o r f o u r b e e f cow __ _____________________________D a te 30 d p o s t c a lv in g 7/18 HH 6 .6 1 + 0 .7 3 ^ 6 .1 0 + 0 .3 6 b 7 .9 8 + 0 . 3 6 5 .6 3 + 0 .4 0 b TH 7 .7 3 + 0 . 8 l b 9.09 + I . O l c 8 .5 3 + 0 .7 1 7 . 8 0 + 0 . 7 1 cd T(SH) 1 2 .5 3 + 2 . 1 4 c 8 .7 4 + 0 .7 8 ° 7 .6 2 + 1 .1 6 8 .1 6 + 0 . 4 7 d C(SH) 8 . 4 9 + I .1 3 b 8.41 + 0 . 9 7 ° 8 .8 9 + I .06 6 . 3 5 + 0 . 9 5 bc 8 /2 2 9 /3 0 a L e a s t s q u a r e m eans ±_ SE. b c d Means w i t h i n a colum n w i t h d i f f e r e n t s u p e r s c r i p t d i f f e r ( P t . 10). 36 T a b l e 15. C a l f a v e r a g e d a i l y g a i n (k g ) from dams o f f o u r d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s , 1986a B i o l o g i c a l . _____________________________ P e r i o d 30 d type p o st c a lv in g B i r t h - 30 d 7 /1 8 - 8 /2 2 - 7/18 D ost c a l v i n g 8/2 2 - 0 .8 5 + .0 5 ° O cr 0 .6 8 + .07 TH 0 .8 6 + .06 0 .9 9 + . 0 4 c 0 .9 8 + .0 7 c 0 .7 4 ± .0 4 T(SH) 0 .9 2 + .01 1 .0 5 + .0 3 ° 1+ . UO O 0 .8 9 + .0 4 C(SH) 0 .8 2 + .0 9 1 .0 0 + .0 6 ° +1 Zf O O CU O 0 .8 8 + .06 _ O 1+ CO O Ul 0 . 7 2 + .03 oo HH O 9/3 0 a L e a s t s q u a r e m eans +_SE. bcMeans w i t h i n a colum n w i t h d i f f e r e n t s u p e r s c r i p t d i f f e r (P < .0 5 ). A lo n g w ith b io lo g ic a l - ty p e , sex of c a lf and sp le e n w e ig h t a c c o u n t e d f o r 65% o f t h e v a r i a t i o n i n m i l k p r o d u c t i o n ( T a b l e 1 6 ) . When b i o l o g i c a l t y p e was n o t i n c l u d e d a s a m ain e f f e c t s e x o f c a l f , cow ADG, body c o n d itio n and hot carcass w e ig h t a cco u n ted fo r 52% of th e v a r i a t i o n i n m ilk p r o d u c tio n (T ab le 1 7 ). A ve ra g e d a i l y g a i n f o r t h e cows ( T a b l e 18) s t e a d i l y i n c r e a s e d fro m th irty d a y s p o s t c a l v i n g t o A ugust 2 2 , y e t an a v e r a g e d e c r e a s e i n body w e i g h t o f .9 5 k g / d o c c u r r e d d u r i n g l a t e r A u g u st and i n S e p te m b e r. O rg a n ic m a tte r in ta k e d id not ( P > .1 0 ; T a b l e 19) i n e i t h e r p e r i o d . d iffe r IVOMD f o r t h e f i r s t p e r i o d was e s t i m a t e d a t 42%, and 35% f o r t h e s e c o n d p e r i o d . was 6.1% d u r i n g A u g u s t , ty p es T h i s was a l s o t r u e when i n t a k e was e x p r e s s e d a s a p e r c e n t o f body w e i g h t . forage among b i o l o g i c a l Crude p r o t e i n o f t h e and 7% i n S e p t e m b e r . A cid d e t e r g e n t f i b e r was 39% and 45% i n A u g u s t and S e p te m b e r r e s p e c t i v e l y . A cid 37 T a b l e 16. S te p w ise r e g r e s s i o n c o e f f i c i e n t s f o r m ilk p ro d u c tio n a t w e a n i n g , 1986 V a ria b le B0 B1 13-6956 1 6 .0 3 8 0 1 7 .4 9 1 3 1 4 .8 6 3 6 13-3189 7 .0 3 0 0 -1 .8 2 5 0 eeie 0 .5 1 7 4 1 .9 7 0 6 * “ * -0 .6 6 3 0 - 2 . 2 0 1 8a “ *“ -8 .4907«* HH TH T(SH) C(SH) Sex o f c a l f S p leen w eig h t MSB 1 .7 0 6 3 R2 0 .6 5 4 6 * “ * a The c l a s s v a r i a b l e Sex i s s c o r e d : I= H e ife r c a l f , P = S teer c a lf. * PC.10. «" P C .0 5 . eiettPC .01 . T ab le 17. S tep w ise r e g r e s s i o n c o e f f i c i e n t s f o r m ilk p r o d u c tio n a t w e a n i n g , 1986 V a ria b le Bo Sex o f c a l f Cow ADG C o n d itio n s c o re Hot c a r c a s s w e i g h t 3 0 .3 8 7 6 3 4 .6 8 0 5 2 5 .1 2 0 4 3 5 .0 8 1 3 B1 -1 .7766* 2 .5 1 2 2 * _ 9 .8944“ “ 0 .0 6 6 5 ” MSB 2 .2 2 5 8 R2 0 .5 2 3 0 “ * a The c l a s s v a r i a b l e Sex i s s c o r e d : c a lf. *» P C .0 5 . e e P C .0 1 . I= H e ife r c a l f , P = S teer 38 T able 18. A v e ra g e d a i l y g a i n ( k g ) o f f o u r d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s , 1986ab P e rio d B io lo g ic a l type ' 30 d post c a lv in g - 7 /1 8 7 / 1 8 - 8 /2 2 HH 0 . 7 0 + .1 8 0 . 7 0 + .06 TH 0 .7 1 + .11 0 .6 7 + .17 - 0 . 8 7 + .0 9 T(SH) 0 .5 7 + -13 0 .4 7 + .13 - 0 . 9 6 + -11 C(SH) 0 .6 3 + .2 4 0 . 9 8 + .15 - 1 .21 + -11 VD I ♦' O 8 /2 2 - 9 / 3 0 + .1 8 a L e a s t s q u a r e m eans +. SE. bP > .1 0 . T ab le 19. O r g a n ic m a t t e r i n t a k e ( k g ) p e r day ( O M l / d ) , and OMI/d a s p e r c e n t o f body w e i g h t (%BW) f o r f o u r b e e f cow b i o l o g i c a l t y p e s , 1986ab -i D a te B io lo g ic a l ty p e 7 / 2 4 - 7 /3 1 OMI/d.%BW OMI/d 9/21 - 9 /2 9 O M I / d BW OMI/d HH 7 . 7 9 + 0 .6 6 1 .43 + 0 . 1 3 6 .8 0 + 0 .4 4 1 .3 2 + 0 .0 9 TH 7 .6 8 + 0 . 8 6 1 .4 0 + 0 . 1 6 7 .7 3 + 0 .4 8 1 .5 0 + 0 . 0 8 T(SH) 7 .1 4 + 0 . 7 1 1.31 + 0 - 1 4 6 . 7 0 + 0 .5 6 1 .3 2 ,+ 0 .1 2 C(SH) 6 .9 3 + 0 . 7 2 1 .1 8 + 0 . 1 7 8 ,3 0 + 0 . 6 0 I .53 + 0 . 1 0 a L e a s t s q u a r e m eans +_SE. bP > . 1 0 . 39 d e t e r g e n t l i g n i n was 5.2% i n b o t h A u g u s t and S e p t e m b e r . Sex o f c a l f , c a l f a g e , cow ADG p r i o r t o w e a n in g and k i d n e y w e i g h t a c c o u n t e d f o r 62% o f t h e v a r i a t i o n f o r OMl ( T a b le 2 0 ) . T ab le 2 0 . S tep w ise r e g r e s s i o n c o e f f i c i e n t s f o r o r g a n ic m a t te r i n t a k e a t w e a n i n g , 1986 V a ria b le Bd . 5 .2 0 5 2 6 .1 0 0 2 7 .6 7 5 7 -2 .2 5 3 5 Sex o f c a l f Age o f c a l f Cow ADG p r i o r t o w e a n in g K id n ey w e i g h t B1 - 0 . 9 4 9 1 aett - 0 .0 4 9 9 « = * * 1 .5 2 5 6 = " 8 .4036*= * MSE 0 .8 5 7 8 R2 0 .6 1 9 9 * « * a The c l a s s v a r i a b l e Sex i s s c o r e d : I = H e i f e r c a l f , 2 = S t e e r c a lf. * P < .1 0 . »* P< . 0 5 . * * * P < .0 1 . The k i d n e y s p r o v e d t o be l a r g e r ( P < .0 5 ) i n th e - C(SH) g r o u p t h a n i n t h e e i t h e r t h e HH o r TH a n i m a l s , w h e r e a s t h e T(SH) g r o u p was s i m i l a r t o bo th e x tre m e s (T ab le 2 1 ) . for s p le e n w eig h t k idney was no as w e ll. lo n g er T h i s p a t t e r n was r e p e a t e d a t t h e P < .1 0 l e v e l When e x p r e s s e d d iffe re n t (P > .1 0 ), d i f f e r e n t w ith o u t a change in ra n k . as a %BW ( T a b le how ever D ifferen ces th e sp le e n ( P > .1 0 ) o r g a n w e i g h t s among b i o l o g i c a l t y p e s w e re n o t d e t e c t e d . 2,2) th e r e m a in e d in th e o th e r R e t ic u l o r u m e n volum e a l s o d i d n o t v a r y ( P > .1 0 ) among b i o l o g i c a l t y p e s ( T a b l e 2 3 ) . 40 T able 21. Organ m ass o f f o u r d i f f e r e n t b e e f b i o l o g i c a l cow t y p e s , 1986a H eart B io lo g ic a l type S p leen Lung L iv e r Kidney - R eticulorum en 0CVi 3-17 + .18 0 .60 TH I .85 + .05 I .02 5.8 0 + .18 3 .0 2 + -15 0 .5 8 + .0 2 d T(SH) 1.92 + .04 I .08 + .04bc 5 .6 8 + .17 3-55 + -37 0.67 + .0 4 Ce 15.35 ± 0.71 C(SH) 2.07 + •' .05 1.21 6.00 + *27 3 .24 +. • 16 0.76 + .0 5 e +1 VO 1+ O 5.40 + .11. +I 0.97 + .02b O I .92 + .07 in 15.27 + 0 .6 9 HH 14.70 ± 1.04 16.71 + 0 .7 6 a L e a st sq u a re means +_ SE. bcMeans w ith in a column w ith d i f f e r e n t s u p e r s c r i p t d i f f e r (P < .1 0 ) . c e Means w ith in a column w ith d i f f e r e n t s u p e r s c r i p t d i f f e r (P < .0 5 ) . T ab le 2 2 . O rgan m ass a s a p e r c e n t o f body w e i g h t o f f o u r d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s , 1986a B io lo g ic a l type H eart Kidney L iv e r . ---------------------- _________---- ------------ Lung S p leen R eticulorum en JtBW ______---- -—__—------------- ------------------O 0 .12 + .004bc 2.95 + .131 1 .04 + .016 0.61 TH 0.36 + .008 0.2 0 t .004 1.13 + .024 0 .5 8 + .020 0.11 + .004b ' 2.84 + .138 + .002 0.21 + .008 1 .12 + .033 0.70 + .069 0.13 + .008° 3-02 + .131 0.37 + .012 0.2 2 + .016 1.07 + .041 6.5 8 + .016 0.13 + .004? 2.99 + .131 T(SH) C(SH) +1 0.1 9 t .004 - CO m 0.37 + .012 O HH a L ea st sq u a re means +_ SE. bcMeans w ith in a column w ith d i f f e r e n t s u p e r s c r i p t d i f f e r (P< .0 5 ) . 41 T ab le 23. P o t e n t i a l r e t i c u l o r u m e n volum e o f f o u r d i f f e r e n t b e e f cow b i o l o g i c a l t y p e s , 1986a B io lo g ic a l ty p e R e t ic u l o r u m e n Volume ------------I ---------- - HH 6 3 .3 4 + TH 6 8 .3 7 + 13-57 T(SH) 7 0 .3 7 + 4 .5 2 C(SH) 8 0 .6 3 + 3 .0 9 4 .6 7 a L e a s t s q u a r e m eans +_SE. bP X I O . J 42 DISCUSSION Forage In ta k e Forage i n ta k e f o r a l l low er th an b io lo g ic a l ty p es in v a l u e s r e p o r t e d by Wagner e t a l . Wagner u s i n g t h e same l a c t a t i n g 1985 was s u b s t a n t i a l l y (1 9 8 6 ) f o r 1983 and 1984. b i o l o g i c a l t y p e s and p a s t u r e rep o rted OMI t o be c l o s e r t o 2.3% body w e i g h t i n A u g u s t , 1 9 8 3 , and 2.0% o f body w e i g h t i n A u g u s t , 1984. 57% i n 1984. 1982 u s i n g F o r a g e IVOMD was e s t i m a t e d a t 59% i n 1983, and K ronberg e t . la c ta tin g a l. HH and (1 9 8 6 ) 3S1H on fo und somewhat l o w e r OMl d u r i n g th e same p a stu re used in 1985. They r e p o r t e d OMI a t 1.7% o f body w e i g h t f o r HH co w s, and 1.9% f o r 3S1H cow s. Forage The i n c r e a s e d ig e stib ility in forage for q u a lity K ronberg's in stu d y was 41% i n 1983 and 1984 seem s t o A u g u st. account fo r t h e d i f f e r e n c e s i n i n t a k e o v e r 1982, y e t d o e s n o t a c c o u n t f o r t h e much lo w er in ta k e in 1 985. Work by F u n s t o n e x p l a n a t i o n f o r t h e low 1985 i n t a k e s (1987) found. may o f f e r Fu n sto n a p o ssib le (1 9 8 7 ) u sin g an a d j a c e n t p a s t u r e and t h e same b i o l o g i c a l t y p e s i n 1985 r e c o r d e d g r a z i n g tim es th a t exceeded fatig u e lim its fo u n d by S c a rn e c c h ia a p p r o a c h e d f a t i g u e l i m i t s fo u n d by S t o b b s ( 1 9 7 5 ) . of 1 1 .9 lim ite d hours per in ta k e . day su g g ests th a t fatig u e (1985), and O v e ra ll g ra z in g tim e rath e r th an rumen fill F u n sto n f e l t t h a t in a d e q u a te fo ra g e a v a i l a b i l i t y (d u e t o s u c c e s s i v e d r o u g h t y e a r s ) was a m a j o r c a u s e o f t h e e x t e n d e d g r a z i n g tim e s. P r e c i p i t a t i o n i n 1985 was 2 8 .7 4 cm, o r 57% o f n o r m a l , w i t h l e s s t h a n 30% o f t h e r a i n f a l l b e i n g r e c e i v e d p r i o r t o o r d u r i n g t h e g r o w in g season. L athrop (1985), i n a c o m panion s t u d y t o W agner e t a l . (1 9 8 6 ) \ 43 reco rd ed g ra z in g o f 9 .4 h /d . tim e s in 1984 and r e p o r t e d o v e r a l l mean g r a z i n g t i m e L a t h r o p ' s r e s u l t s s u g g e s t t h a t f a t i g u e was n o t a l i m i t i n g f a c t o r t o t h e i n t a k e v a l u e s fo u n d by W agner e t a l . O r g a n ic m a t t e r in ta k e a lth o u g h h ig h e r th a n was h i g h , w ith for th e b io lo g ic a l 1985, was a l s o g razin g tim e lo w . e stim a te s s t u d y b e i n g 1 1 .3 h / d ( F u n s t o n , 1 9 8 7 ) . a p p ro x im a te ly 1 ,2 0 0 k g DM/ha, lim itin g in ta k e (F u n sto n , 1 9 8 7 )• was s i m i l a r t o K r o n b e rg e t a l . (1 9 8 6 ) i n 1984. types, s tu d ie d O v e ra ll of th e d a ily same 1986, g razin g tim e cows w i t h i n th is H ow ever, f o r a g e a v a i l a b i l i t y was w hich su g g e sts th at fatig u e Forage d i g e s t i b i l i t y (1 9 8 6 ) in was not i n J u l y o f 1986 i n A u g u st o f 1 9 8 2 , t h i s may mean f o r a g e r e a c h e d m a t u r i t y e a r l i e r i n t h e y e a r and c o n t i n u e d t o d r o p s i n c e IVOMD e s t i m a t e s i n S e p t e m b e r , 1986 w ere 35%. p ro te in , a c id d e t e r g e n t f i b e r and p e r c e n t l i g n i n m a t u r e f o r a g e s low i n d i g e s t i b i l i t y W ith th e se in h ib ito ry (H o d g so n , a n im a l lo w fo rag e p h y sic a l 1985). sw ard sa tie ty McClymont g e n e tic p o te n tia l. (1 9 6 7 ) w h ic h suggest th a t S e le c tiv ity for fe lt.th a t demands due in d e c lin in g r a te of in ta k e . cows may e x p l a i n due s im ila r to o th er a l . , 1985; W h it e , 19 8 3 ) • v a lu e s response are it to seem s rum en lik e ly fill an o ccu rred two m ec h a n ism s l i m i t im posed upon t h e a n im a l th e by its A l i m i t a t i o n o f d i g e s t i v e c a p a c i t y f o r low q u a l i t y And l i m i t a t i o n s c o n d itio n s, (Jung, e t. d ig e s tib ility from m e e t i n g n u t r i e n t fo rag es. E s tim a te s o f fo ra g e crude p lan t tu rn b e h a v io ra l m o d ifie s a d a p tio n g razin g to tim e lim itin g a o ffset a to I n c r e a s e d s e l e c t i v i t y by young i n e x p e r i e n c e d e x te n siv e g raz in g to g razin g b e h a v io r p a rts, tim e s lim ite d fo u n d in ta k e sp e c ific a lly le a f in 1986, rath e r over w hich th an ste m GI and a lso fill. green m a t e r i a l o v e r d e a d h a s b e e n fo u n d t o i n c r e a s e g r a z i n g t i m e and d e p r e s s 44 in ta k e ( M in s o n , 1 986 s u p p o r t s sta n d in g areas th at C asual had near c o n d itio n s been th e in o b se rv a tio n s a h ig h d eg ree o f bio m ass a p p e a re d th a t tille rs 1981). base 1985 of a n im a ls grazed, b u n chgrass w here sta n d in g th e stu d y a n im a ls se le c tio n o ccu rred . su ffic ie n t p re v io u sly of or spent m ore se le c te d sp e cie s. bio m ass was Even t h o u g h tim e green T h is is g raz in g v e g e ta tiv e opposed u n ifo rm ly g r o u n d , and was composed o f v e g e t a t i v e t i l l e r s . in low to to S e l e c t io n d u rin g th e 1985 appeared m in im a l. M ilk P r o d u c t i o n M ilk p r o d u c t i o n f o r a l l b i o l o g i c a l , t y p e s was g r e a t e r i n 1985 t h a n fro m t h e In A ugust same b i o l o g i c a l 198 4 , from 2 k g / d h ig h er for fo rag e t y p e s u s e d by Wagner e t . Wagner e t . a l. 1S3H cows t o q u a lity la rg e r re s p o n sib ility in 1984 (1 9 8 6 ) a h ig h it is fo u n d m i l k o f 8 .2 k g /d p o ssib le A n so teg u i (1 9 8 6 ) (1 9 8 6 ) in 1984. p ro d u ctio n for th a t f o r n u t r i e n t in ta k e th an in f o r a g e q u a l i t y was lo w . a l. SH cow s. c a lv e s ran g in g W ith assum ed a 1985 o r i n 1986 when fo u n d t h a t f o r a g e i n t a k e t o c o m p e n s a te f o r r e d u c e d m i l k i n t a k e . c a lv e s in creased The o p p o s i t e may a l s o be t r u e i n t h a t c a l v e s may i n c r e a s e o r m a i n t a i n h i g h e r m i l k i n t a k e l e v e l s when f o r a g e s l i m i t m e t a b o l i z a b l e e n e r g y i n t a k e because of poor forage q u a lity . M ilk p r o d u c t i o n r e m a in e d h i g h d e s p i t e lo w , o r i n forage q u a lity . Forage i n ta k e d a ily g a in s th e m ain ta in m ilk of cows p ro d u ctio n . in creased in d ic a te ,th a t L a c ta tio n to some e x t e n t , body ta k e s 1986, d e c re a s in g c o n d itio n p recedence yet average d ecreased over to o th e r 45 m e ta b o lic f u n c t i o n s even t o th e p o in t o f m e ta b o lic d y s fu n c tio n I 98O ) . and C u r r i e , T h is i s in d ic a te d by t h e l o w e r c a r c a s s w e i g h t s o f t h e s t u d y a n i m a l s w i t h c a l v e s o f h i g h e r w e a n in g w e i g h t s . th a t th e carcass is a m ajo r p ro d u ctio n . K id n e y p ro d u ctio n p o te n tia l fat was in a lso 1985. p r e v i o u s l y (H am m ond,'1947;, in so u rce of n u trie n ts reduced T hese in T his s u g g e s ts f o r m a in ta in in g m ilk cows w i t h o b se rv a tio n s B o tts e t a l . c o n d itio n i s ex p ected d u rin g l a t e (Bauman 1979). h ig h er m ilk been n o ted have G e n e r a l ly , an i n c r e a s e l a c t a t i o n and d u r i n g n o n l a c t a t i n g p e r i o d s i f n u t r i t i o n a l and e n v i r o n m e n t a l c o n d i t i o n s a r e a d e q u a t e (NRC, 1984). Sex of p ro d u ctio n M e lto n c a lf for e t. w as b o th a l. (1 9 6 7 ) d u rin g th e im p o rta n t reg ressio n r e a r i n g m ale c a l v e s was c a lv e s an fo und R u tled g e et a l. m o d e ls th at th e .5 8 k g a b o v e 77 da y p o s t p a r t u m t h i s d i f f e r e n c e d im in ish e d t o (1 9 7 1 ) v a ria b le o f m ilk d a ily th a t of th e p e rio d . th at m ilk in p ro d u ctio n cows r e a r i n g As l a c t a t i o n 1986. of cows h e ife r progressed C o n trary t o t h i s r e p o r t , dams n u r s i n g s i g n i f i c a n t l y m ore m i l k t h a n dams n u r s i n g b u l l e x p la in in g p ro d u ctio n m ilk .1 0 k g p e r d a y . n o ted in h e ife r c a lv e s. c a lv e s gave Over a 205 d l a c t a t i o n p e r i o d H e r e f o r d dams n u r s i n g h e i f e r c a l v e s g a v e a p p r o x i m a t e l y 56 k g m ore m i l k . R e s u l t s o f t h i s s t u d y w ould s u p p o r t t h e i d e a o f dams w i t h h e i f e r s g i v i n g m ore m i l k ( s e e T a b l e 4 ) . Organ m ass D i f f e r e n c e s i n o r g a n m ass among b i o l o g i c a l t y p e s a p p e a r t o r e f l e c t d i f f e r e n c e s i n m ilk p r o d u c tio n p o t e n t i a l i n 1985, w i t h b o t h body s i z e 46 and m i l k p r o d u c t i o n i n f l u e n c i n g o r g a n m ass i n th e k id n ey s p ro d u ctio n and th e liv e rs p o te n tia l. The w ere larg e r re la tiv e siz e 1986. in of D u r in g 1985 b o t h cows w i t h th e se h ig h er organs m ilk rem a in e d s i g n i f i c a n t when s c a l e d t o b o t h body w e i g h t and m e t a b o l i c body w e i g h t . T h i s was a s e x p e c t e d s i n c e b o t h o r g a n s a r e known t o i n c r e a s e d u rin g l a c t a t i o n a s opposed t o a n o n l a c t a t i n g s t a t e 1974), im p ly in g p o te n tia ls. observed b e in g d iffe re n c es may e x ist w ith in siz e (S m ith and B a ld w in , d iffe re n t la c ta tio n D u r i n g 1986 d i f f e r e n c e s i n body s i z e seem ed t o a c c o u n t f o r d iffe re n c e s d iffe re n t in th e k idney among b i o l o g i c a l w e ig h ts, ty p es. The w ith liv e r w e ig h ts sig n ific a n c e of not sp le e n w e i g h t on m i l k p r o d u c t i o n (1 9 8 6 ) and OMI (1 9 8 5 ) i s n o t u n d e r s t o o d . L iv e r w e ig h ts rep o rted by S m ith and B a ld w in (1 9 7 4 ) f o r a 700 kg l a c t a t i n g cow w e re 1 1 .4 k g , n e a r l y t w i c e t h e s i z e o f t h e l i v e r w e i g h t s r e p o r t e d i n t a b l e s 8 and 2 0 . t i s s u e " " I x d""^ i s assum ed I f an e n e r g y v a l u e o f 3 7 0 . 2 k c a l x k g o f ( S m ith and B a l d w i n , 1974), th en th e l a r g e r l i v e r o f t h e SH r e p r e s e n t s a 9% i n c r e a s e i n l i v e r m a i n t e n a n c e o v e r t h e s m a l l e s t mean l i v e r w e i g h t (HH). A a d d i t i v e e f f e c t may o c c u r i f o t h e r sm a lle r d i f f e r e n c e s are c o n sid e re d . D u r in g 1985 re tic u lo ru m e n w eig h t d id n o t d i f f e r ( P > .1 0 ) be e x p e c t e d fro m p r e v i o u s s t u d i e s ( S m i t h and B a l d w i n , 1 9 7 4 ) . a s m ig h t W eight o f t h e r e t i c u l o r u m e n a p p e a r s t o be c l o s e l y a s s o c i a t e d w i t h t h e i n c r e a s e i n feed in ta k e d u rin g la c ta tio n demand w i t h l a c t a t i o n d id not d i f f e r rath e r th an (C a m p b e ll and F e l l , among b i o l o g i c a l th e in cre ase 1964). e n e rg e tic S in ce fo ra g e i n ta k e ty p es in e i t h e r y e a r, r e t i c u l o r u m e n w e i g h t was n o t e x p e c t e d . in a d ifferen ce in 47 S in ce organ t h e y may n o t w e ig h ts be s i m i l a r w e re to observed d u rin g l a c t a t i o n . not th e o b tain ed d u rin g la c ta tio n d i f f e r e n c e s w h ic h m ig h t of in 1985 have been Due t o h i g h e r e n e r g y demands f o r l a c t a t i o n (NRC, 1984) o r g a n w e i g h t s may h a v e b e e n g r e a t e r i f m e a s u r e d e a r l i e r . Our o b s e r v a t i o n s do i n d i p a t e t h a t d i f f e r e n c e s i n o r g a n m ass e x i s t among b i o l o g i c a l t y p e s when i n a n o n l a c t a t i n g s t a t e . G r e a t e r d i f f e r e n c e s may h a v e a l s o b e e n o b s e r v e d d u r i n g p e a k l a c t a t i o n when d i f f e r e n c e s i n m i l k p r o d u c tio n a r e found to o c c u r . R e t i c u l o r u m e n Volume A lth o u g h p o s s i b l e fill l i m i t a t i o n s may h a v e l i m i t e d i n t a k e d u r i n g 1986 f o r a g e i n t a k e d i d n o t v a r y ( P > .1 0 ) among b i o l o g i c a l t y p e s . sam e resp ect reticu lo ru m en volum e a lso su g g ests a p o ssib le r e la tio n s h ip e x is te d . th is h y p o th e sis needs to be d id not v ary In th e (P X IO ) w hich How ever, f u r t h e r t e s t i n g a c c o m p lish e d b efo re any of d e fin itiv e c o n c l u s i o n s c a n b e m ade. G eneral D is c u ss io n T h e s e r e s u l t s s u g g e s t t h a t a s s e s s i n g d i f f e r e n c e s i n v i s c e r a l m ass may lea d la c ta tin g to a beef b e tte r cow u n d e rsta n d in g and a ssist b i o l o g i c a l t y p e s o f b e e f cow s. in of th e to ta l q u a n tify in g of d iffe re n c e s th e am ong S e v e r a l im p ro v e m e n ts i n f u t u r e r e s e a r c h a re su g g ested to b e t t e r d e fin e th e s e r e l a t i o n s h i p s . several e n e rg e tic s D u rin g t h i s c o n f o u n d i n g f a c t o r s may h a v e i n f l u e n c e d o u r r e s u l t s . stu d y R e su lts 48 c o n c e r n i n g t h e w e i g h t o f t h e l i v e r w e re l i k e l y t o be i n f l u e n c e d by t h e fa stin g to s ta te tim e i n w e re o f t h e a n im a l b e f o r e e x s a n g u i n a t i o n . tra n sit o b tain e d and t o w e re lik e ly (1 9 7 2 ) f o u n d t h e t o t a l purchased fro m dry l o t to c o n d itio n s affect sh rin k ag e in a rancher liv e r T issu e b efo re s h r i n k due v i s c e r a l w e ig h ts w e ig h t. S e lf and N e ls o n s t e e r s was a p p r o x i m a t e l y 7 .2 $ when and t r a n s p o r t e d fro m 150 t o 1133 m i l e s . A l a r g e p o r t i o n o f t h i s s h r i n k can be a t t r i b u t e d t o e x c r e t o r y S h r in k , y e t any t i s s u e sh rin k th a t occurred i s lik e ly to have i t s on t h e w e i g h t o f t h e l i v e r b e f o r e a f f e c t i n g and G e r o k , 1 9 8 6 ) . and its rap id g re a te st e ffe c t o th er tis s u e s ( H a u ssin g e r B e c a u se o f t h e r o l e o f t h e l i v e r a s a s t o r a g e o r g a n lo ss of glycogen and p ro te in (B ietz and A llen , 1983; V ernon and P e a k e r , 1983) t h e f a s t i n g and s t r e s s c o n d i t i o n s im posed may have caused a to ta l red u c tio n in liv e r w e ig h t up to 48%. F u rth e r s t u d i e s s h o u l d c o n s i d e r i n s i t u m e a s u r e m e n ts t o e l i m i n a t e t h i s e r r o r . S tre s s as a r e s u l t o f in ta k e in m e a su re m e n ts of v isc e ra l e s t i m a t e s may p r o v i d e f u r t h e r e r r o r organ m ass. T his s tre s s may cause a n e g a t i v e e n e r g y b a l a n c e i n t h e a n im a l t o o c c u r t h e r e b y a f f e c t i n g o r g a n w e ig h ts. n o rm a l In a d d itio n g razin g tim e to is th e added d isru p ted , e ffe c ts h a v in g of stre ss, p o ssib le th e a n im a l's consequences of e x a c e r b a tin g th e a n im a ls n e g a tiv e energy b a la n c e . The e f f e c t s o f t o t a l fecal subsequent c o l l e c t i o n s on t h e g razin g a n im a l and the e stim a te s n e e d t o b e e x a m in ed f u r t h e r and a l t e r n a t i v e m eth o d s t e s t e d . A d d i t i o n a l m e a s u r e m e n ts t h a t i n d i c a t e e x t e n t a n d t y p e o f m e t a b o l i c a c tiv ity p e r u n i t o f t i s s u e w e i g h t may be h e l p f u l . Dry m a t t e r w e i g h t s sh o u ld i n c r e a s e t h e a c c u r a c y o f m e a s u r e m e n ts by l i m i t i n g v a ria tio n tissu e lev e ls. c o u p le d w i t h m o istu re P ro te in c o n te n t of th e v is c e r a in 49 o t h e r m e a s u r e s o f m e t a b o l i c a c t i v i t y may p r o v e t o be a b e t t e r i n d i c a t o r of an a n i m a l ’ s e n e rg e tic su g g ested t h a t t o t a l to th e energy M e a s u re m e n ts am ino a c i d s for c o rre la tio n s m ain te n a n c e RNA c o n t e n t acro ss if e x ist. Tess (1 9 8 4 ) p r o t e i n w e i g h t o f t h e v i s c e r a m ig h t be a r e l a t e d req u ired of sta tu s th e o r enzym es of d iffe re n t re sp o n sib le p la s m a membrane may be sto c k s for usefu l of p ig s. tra n sp o rt in of d ete rm in in g d i f f e r e n c e s i n m a i n t e n a n c e due t o p r o t e i n m e t a b o l i s m . B a ld w in a n d S m ith (1 9 8 3 ) e s t i m a t e d t h e e f f e c t s o f l a c t a t i o n on t h e a c tiv itie s o f l i v e r enzym es i n th e ru m in a n t. T h e se e n z y m a t i c c h a n g e s a s s o c i a t e d w i t h g l u c o n e o g e n e s i s may v a r y among b i o l o g i c a l t y p e s and may be a f a c t o r enzym es i n w hole sh o u ld be c h a ra c te ristic s p art en erg y (B a ld w in and of m e ta b o lism S m ith , 1983), d iffe re n c e s a rea c o n tin u e s. energy p a rtitio n in g . fu tu re among b i o l o g i c a l v isc e ra l u n d e rsta n d in g a body of but stu d ie s ty p e s. among b i o l o g i c a l c o m p a r in g R e g u la to ry ru m in a n ts p ro m ise A ssays are to ty p es of p e rtin e n t th e v isc e ra l m ec h a n ism s c u rre n tly fu rth e r if not known a ssist research in in in th is 50 LITERATURE CITED 51 Adams, D . C . , R .E . S h o r t and B.W. K napp. 19 8 ? . Body s i z e and c o n d i t i o n e f f e c t s on p e r f o r m a n c e and b e h a v i o r o f g r a z i n g cow s. N u t r . Rep. I n t e r . 35:269« A l l i s o n , C .D . 1985. ru m in a n ts: A rev iew . F a c to rs a f f e c tin g fo rag e J . Range M anage. 3 8 : 3 0 5 . in ta k e by body beef range A n so te g u i, R .P ., 1986. C h e m i c a l c o m p o s i t i o n and rumen d i g e s t a k i n e t i c s o f d i e t s s e l e c t e d and i n f l u e n c e o f o f m i l k i n t a k e on f o r a g e i n t a k e by s u c k l i n g c a l v e s g r a z i n g n a t i v e r a n g e . P h .D . D i s s e r t a t i o n , New M exico S t a t e U n i v . , L a s C r u c e s . A r n o l d , G.W. I960. The e f f e c t o f q u a n t i t y and a v a i l a b l e t o s h e e p on t h e i r g r a z i n g b e h a v i o r . 1 1 :1 0 3 4 . A sso c ia tio n o f O f f ic ia l A g ric u ltu re m e th o d s o f a n a l y s i s ( 1 3 t h e d . ) . D.C. q u a lity of p a stu re A u s t . J . A g r. R e s . C h e m ist (AOAC). 1980. O ffic ia l A s s o c . O f f . A g r. Chem. W a sh in g to n B a i l e , C .A . a n d J . M . F o r b e s . 1 974. C o n t r o l o f f e e d i n t a k e and r e g u l a t i o n o f e n e r g y b a l a n c e .in r u m i n a n t s . P h y s i o l . R ev. 5 4 :1 6 0 B a k e r , P . F . and C.M. C o n n e l l y . 1 966. Some p r o p e r t i e s o f t h e e x t e r n a l a c t i v a t i o n s i t e o f t h e sodium pump i n c r a b n e r v e . J . P h y sio l. (L ondon) 1 8 5 : 2 7 0 . B a l a b a n , R . S . , S . P . S o l t o f f , J.M . S t o r e y and L . J . M a n d e z .. 1 9 8 0 . Im proved r e n a l c o r t i c a l t u b u l e s u s p e n s i o n ; s p e c t r o p h o t o m e t r i c s t u d y o f Og d e l i v e r y . Amer. J . P h y s i o l . 2 3 8 : F 5 0 . B a ld w in , R .L . and N .E . S m it h . 1975. M o lecu lar c o n t r o l o f e n e r g y m eta b o lism . I n : J . D . S i r k ( E d .) The C o n t r o l o f M e t a b o l i s m . . pp 17 34. P e n n s y lv a n ia S t a t e U niv. P r e s s , U n iv e r s ity P a rk . B a l d w i n , R . L . a n d N .E . S m ith . 1983. A d a p t i o n s o f m e t a b o li s m t o v a r i o u s c o n d i t i o n s ; M ilk p r o d u c t i o n . I n ; P.M. R i i s ( E d . ) , Dynamic B i o c h e m i s t r y o f Animal P r o d u c t i o n . E l s e v i e r S c i e n c e P u b l i s h e r i n g Co. I n c . New Y ork. B a l d w i n , R . L . , N .E . S m i t h , J . T a y l o r and M.S h a r p . m e t a b o l i c p a r a m e t e r s t o im p ro v e g r o w th r a t e J . Anim. S c i . 5 1 : 1 4 1 6 . B a n c ro ft, S .J . 1947. S p rin g fie ld IL . 1980. M a n ip u la tin g and m i l k s e c r e t i o n . R e s e a r c h e s on p r e - n a t a l l i f e . C h a r l e s C Thomas, B a r d , P. 1961. Op u p t a k e and t i s s u e e n e r g y e x c h a n g e . In: . ( E d . ) , M e d i c a l 'P h y s i o l o g y . C.V. Mosby C o ., S t L o u i s , Mo. P. B ard 52 Bauman, D.B. and W.B. C u r r i e . 1980. P a r t i t i o n i n g o f n u t r i e n t s d u rin g p re g n a n c y and l a c t a t i o n : A r e v ie w o f m e c h a n ism s in v o lv in g h o m e o s t a s i s and h o m e o r h e s i s . J . D a i r y S c i . 6 3 .1 5 1 4 . B e i t z , D.C. and R .S . A l l e n . 1983« C arb o h y d rate m e ta b o lism . I n : M .J . Swenson ( E d . ) , D u k e 's P h y s i o l o g y o f Farm A n im a ls . T e n th e d . pp 375-385. C o r n e ll U niv. P r e s s . I t h i c a , NY. B e l l o w s , R.A. an d R .E . S h o r t . 1978. E f f e c ts o f p re c a lv in g feed le v e l on b i r t h w e i g h t , c a l v i n g d i f f i c u l t y and s u b s e q u e n t f e r t i l i t y . J. Anim. S c i . 4 6 : 1 5 2 2 . B e z n a k , M .J. o rig in s. 1969. R eg ressio n o f c a rd ia c Can. J . P h a r m a c o l. 47;579« h y p ertro p h y B l a x t e r , K .L . 1962. The E n e rg y M e ta b o lis m o f R u m in a n ts . Thomas P u b l . S p r i n g f i e l d I L . of v ario u s C h a rle s C B o t t s , R . L . , R.W. Hemken, and L . S . B u l l . 1979.. P r o t e i n r e s e r v e s i n t h e l a c t a t i n g d a i r y cow. J . D airy S c i . 6 2 /4 3 3 . B r o d y , S. 1945. B i o e n e r g e t i c s and G ro w th . R e in h o ld . New Y o rk , NY. C a m p b e ll, R.M. and B .F . F e l l . 1964. G a s t r o i n te s t in a l hy p ertro p h y in t h e l a c t a t i n g r a t a n d i t s r e l a t i o n s h i p t o fo o d i n t a k e . J. P h y s i o l . 1 7 1 :9 0 . C a n a s , R . , J . J . Romero and R .L . B a ld w in . req u irem e n ts d u rin g l a c t a t i o n in r a t s . 1982. M a in te n a n c e e n e r g y J . N u t r . 1 1 2 :1 8 7 6 . C a s e b o l t , D.G. 1 984. L a c t a t i o n c u r v e s and m i l k p r o d u c t i o n i n b e e f c a t t l e w ith v a ry in g d eg rees of c ro ssb red in flu e n c e . M.S. T h e s i s , M ontana S t a t e U n i v . , Bozeman. C h a c o n , E . , T . H . S t o b b s and R .L . S a n d l a n d . 1976. E stim atio n h e r b a g e c o n s u m p t io n by g r a z i n g c a t t l e u s i n g m e a s u r e m e n t s g r a z in g b e h a v io u r. J . B r i t . G r a s s l. Soc. 3 1 :8 1 . Cook, of of C. W. 1970. E n e rg y B u d g e t o f t h e Range and Range L i v e s t o c k . C o lo r a d o S t a t e U n i v . E x p e r . S t a t . B u l l . TBI09« C o ra h , L .R . 1980. F e e d i n g and n u t r i t i o n o f t h e b e e f b r e e d i n g h e r d . I n : D .C . C h u r c h ( E d . ) , D i g e s t i v e P h y s i o l o g y and N u t r i t i o n o f R u m in a n ts . 2 nd e d . O&C B o o k s, I n c . C o r v a l l i s , OR. D a l e , H .E . 1984. E n e rg y m e t a b o l i s m . I n . R . J . Swenson ( E d . ) . D u k e 'S P h y s i o l o g y o f Farm A n im a ls , T e n th e d . pp 4 2 3 -4 3 1 « C o rn e ll U n iv . P ress. I t h i c a , NY. D i j k s t r a , N.D. 1 9 7 1 . F e e d i n t a k e by g r a z i n g d a i r y co w s. 3« C o m p a riso n o f l a c t a t i n g and d r y p r e g n a n t cow s. N e th . J . A g r. S c i . 1 9 .2 5 7 . 53 D z i u k , H .E . 1983. D ig e s tio n i n th e ru m in an t sto m a c h . I n . M. J . Swenson ( E d . ) , D u k e 's P h y s i o l o g y o f Farm A n im a ls . T e n th e d . pp 320-239C o rn e ll U niv. P r e s s . I t h i c a , . NY. E d d e l s t o n e , D . I . and R . I . Holzman. 1981. Oxygen c o n s u m p t io n by t h e g a s t r o i n t e s t i n a l t r a c t and l i v e r i n new born l a m b s . Am er. J . P h y s io l. 2 4 0 :0 2 9 7 . F e ll, B .F . and T . E . C . W eekes. 19 8 0 . Food i n t a k e a s a m e d i a t o r o f a d a p tio n in th e ru m in al e p ith e liu m . I n . Y. R u c k e b u sc h and P . T h iv e n d s ( E d . ) , D i g e s t i v e P h y s i o l o g y and M e ta b o lis m i n R u m in a n ts . MTP P r e s s , L a n c a s t e r . F e r r e l , C .L . and T .G . J e n k i n s . 1984. E n e rg y u t i l i z a t i o n by m a t u r e , n o n p r e g n a n t , n o n l a c t a t i n g cows o f d i f f e r e n t t y p e s . J . Anim. S c i . 5 8 :2 3 4 . F e r r e l , C .L . and T .G . J e n k i n s . 1 9 8 5 . Cow t y p e an d t h e n u t r i t i o n a l e n v i r o n m e n t , n u t r i t i o n a l a s p e c t s . J . Anim. S c i . 6 1 : 7 2 5 . F e r r e l , C .L . and L . J . body c o m p o s i t i o n 4 1 :9 4 2 . A b s tr . Koong. 1982. E f f e c t o f p r e v i o u s n u t r i t i o n on and e n e r g y u t i l i z a t i o n o f r a t s . Fed. P ro c. F e r r e l , C . L . , L . J . Koong and J . A . N i e n a b e r . 1986. E f f e c t,o f p rev io u s n u t r i t i o n on body c o m p o s i t i o n and m a i n t e n a n c e e n e r g y c o s t o f g r o w in g l a m b s . B r . J . N u t r . 5 6 : 5 9 5 . F o r b e s , J .M . 1986. The e f f e c t s o f s e x h o r m o n e s , p r e g n a n c y a n d l a c t a t i o n on d i g e s t i o n , m e t a b o li s m and v o l u n t a r y f o o d i n t a k e . In: L . P. M i l l i g a n , W .L. Grovum a n d A. D o b s o n ( E d . ) , C o n t r o l o f D i g e s t i o n and M e ta b o lis m i n R u m in a n ts . P r e n t i c e - H a l l , Englewood C l i f f s , NJ. F r i s c h , J . E . and J . E . V e r c o e . 197 6 . M a in te n a n c e r e q u i r e m e n t s , f a s t i n g m e t a b o l i s m and body c o m p o s i t i o n i n d i f f e r e n t c a t t l e b r e e d s . In: M. V e rm orel ( E d . ) . E n e rg y M e ta b o lis m i n Farm A n i m a l s , pp 2 0 9 - 2 1 2 . B u s s a c , C le rm o n t-F e rra n d . F u n s t o n , R .N . 1 9 8 7 . G ra z in g b e h a v io r o f r a n g e la n d b e e f d i f f e r i n g in b io lo g ic a l ty p e . M.S. T h e s i s , M ontana S t a t e Bozeman. c a ttle U n iv ., G a r l i c k , P . J . , T .L . Burk and R.W. S w ic k . 197 6 . P r o t e i n s y n t h e s i s and RNA i n t i s s u e s o f t h e p i g . Amer. J . P h y s i o l . 2 3 0 : 1 1 0 8 . G a r r e t t , W.N. 1 971. E n e rg etic e f f ic ie n c y J . Anim. S c i . 3 2 : 4 5 1 . G r e g o r y , K .E . "P u ttin g i t 1972. B eef a ll to g e th e r." o f b e e f and d a i r y c a t t l e t y p e f o r maximum J . Anim. S c i . 3.4.881. ste e rs. efficie n cy . 54 G u e r n s e y , D .L . and E .D . S t e v e n s . 1977. The c e l l membrane sodium pump a s a m e c h a n ism f o r i n c r e a s i n g th e rm o g e n e s is d u rin g c o ld a c c lim a tio n in r a t s . S c ie n c e 1 9 6:908. Hammond, J . 1947. Animal e n v iro n m e n ta l c o n d it io n s . H a r r i s , L .E . 197 0 . w ild ru m in a n ts . b reed in g in r e l a t i o n B i o l . R ev. 2 2 : 1 9 5 . to n u tritio n and N u t r i t i o n a l r e s e a r c h t e c h n i q u e s f o r d o m e s t i c and V o l. I . L .E . H a r r i s P u b . , L o g a n , UT. H a u s s i n g e r , D. and W .G erok. 1986. M e ta b o lis m o f am ino a c i d s and ammonia. I n : R.G. Thurm an, F .C . K auffm an and K. Ju n g e rm a n n ( E d . ) , R e g u l a ti o n o f H e p a tic M e ta b o lis m : I n t r a - and I n t e r c e l l u l a r m eta b o lism . Plenum P r e s s . New Y ork. H a v s t a d , K.M. and J . C . M a le c h e k . 1 982. E n e rg y e x p e n d i t u r e by h e i f e r s g ra z in g c re s te d w h eatg rass o f d im in ish in g a v a i l a b i l i t y . J . Range M anage. 3 5 : 4 4 7 . H a v s t a d , K .M ., A .S . N a s t i s and J . C . M a le c h e k . 1983. The v o l u n t a r y fo ra g e i n ta k e o f h e i f e r s g r a z in g a d im in is h in g su p p ly o f c r e s t e d w h eatg rass. J . Anim. S c i . 3 5 :4 4 7 « H odgson, J . and W.S. J a m i e s o n . 1981. V a r i a t i o n s i n h e r b a g e m ass and d i g e s t i b i l i t y , and t h e g r a z i n g b e h a v i o r and h e r b a g e i n t a k e o f a d u l t c a t t l e and weaned c a l v e s . G r a s s and F o r . S c i . 36:39« H odgson, J . ru m in a n t. 1 985. The c o n t r o l o f h e r b a g e P r o c . N u tr . S p c . 4 4 :3 3 9 . in ta k e in th e g razin g H u n t i n g t o n , G.B. and P . J . R e y n o ld . 1986. Net a b s o r b t i o n o f g l u c o s e , L - I a e t a t e , v o l a t i l e f a t t y a c id s and n i t r o g e n o u s com pounds by b o v in e g i v e n a b o m a s a l i n f u s i o n s o f s t a r c h o r. g l u c o s e . J . D airy S c i . 6 9 :2 4 2 8 . Jung, H .G ., R.W. R ic e and L . J . Koong. 1985. C o m p a riso n o f h e i f e r w e i g h t g a i n s and f o r a g e q u a l i t y f o r c o n t i n u o u s and s h o r t d u r a t i o n g r a z in g sy ste m s. J . Range M anage. 3 8 : 1 4 4 . . K a r t c h n e r , R . J . and C.M. C a m p b e ll. 1979« I n t a k e and d i g e s t i b i l i t y o f r a n g e f o r a g e s consumed by l i v e s t o c k . , M ontana A g r. Exp. S t a . B u ll. 718. K l o s t e r m a n , E .W ., L .G . S a n f o r d an d C .F . P a r k e r . 1968. E f f e c t o f s i z e , b r e e d and s e x upon f e e d e f f i c i e n c y o f b e e f c a t t l e . J . Anim. S c i . 27:2 4 2 . K n i g h t , D.H. 1967. P u lm o n a ry h y p e r t e n s i o n and l e f t v e n t r i c l e a t r o p h y in dogs w ith sp o n ta n e o u s c o r p u lm o n a le . P h y s i o l o g i s t 1 0 :223. 55 K oong, L . J . , C .L . F e r r e l and J . A . N i e n a b e r . 1985. A s s e s s m e n t o f i n t e r r e l a t i o n s h i p s among l e v e l s o f i n t a k e and p r o d u c t i o n , o r g a n s i z e and f a s t i n g h e a t p r o d u c t i o n i n g r o w in g a n i m a l s . J . N u tr. 115 :1 3 8 3 . K re s s* D .D ., D .E . D o o rn b o s and D. A n d e r s o n . 1986. P ro d u c tiv ity of d i f f e r e n t b i o l o g i c a l t y p e s o f b e e f c a t t l e u n d e r M o n ta n a r a n g e c o n d i t i o n s : An i n t r o d u c t i o n . M ontana A g R e se a rch 3 ( 1 ) : I . K r o n b e rg ,. S .L . 1 983 . F o r a g e i n t a k e o f H e r e f o r d and 75% Simraental-25% H e r e f o r d cows g r a z i n g M ontana f o o t h i l l r a n g e l a n d . M.S. T h e s i s , M ontana S t a t e U n i v . , Bozeman. K r o n b e r g , S . L . , K.M. H a v s t a d , E .L . A y e rs and D .E . D o o r n b o s . 1986. I n f l u e n c e o f b r e e d on f o r a g e i n t a k e o f r a n g e b e e f co w s. J . Range M anage. 3 9 : 4 2 1 . L a s t e r , D . B . , G.B. S m ith and K .E . G r e g o r y . 1976. C h a ra c te riz a tio n of b io lo g ic a l ty p es of beef c a t t l e . IV . P o s t w e a n i n g g r o w t h a n d p u b erty of h e if e r s . J . Anim. S c i . 4 3 :6 3 « L a t h r o p , W .J. 1985. G r a z i n g b e h a v i o r o f r a n g e l a n d b e e f cows d i f f e r i n g i n m i l k p r o d u c t i o n . M.S. T h e s i s , M ontana S t a t e U n i v . , Bozeman. L in z e ll, J .L . v o litile 1 5 3 :4 9 2 . I960. Mammary-gland b l o o d flo w and o x y g e n , g l u c o s e and f a t t y a c id u p tak e i n th e c o n sc io u s g o a t. J . P h y sio l. L o b l e y , G . E . , V. M il n e , J.M . L o v i e , P . J . Reeds and K. P e h n i e . 1980. Whole body and t i s s u e p r o t e i n s y n t h e s i s i n c a t t l e . B r i t . J . N u tr. 4 3 :4 9 1 . Lomax, M.A. and G.D. B a i r d . 1 983 . B lood flo w and n u t r i e n t e x c h a n g e a c r o s s t h e l i v e r and g u t o f t h e d a i r y cow. E f f e c t s o f l a c t a t i o n and f a s t i n g . B r i t . J . N u tr. 4 9 :4 6 1 . M c B rid e , B.W. and L .P . M i l l i g a n . 19 8 5 a . E f fe c t o f v i a b i l i t y o v a b a in s e n s i t i v e r e s p i r a t i o n o f lamb h e p a t o c y t e s . I n t e r n . J . B iochem . 17 :4 3 . M c B r i d e , B.W. a n d L . P . M i l l i g a n . 1985b. M a g n itu d e o f o v a b a i n s e n s i t i v e r e s p i r a t i o n in th e l i v e r o f g r o w in g , l a c t a t i n g and sta rv e d sheep. B r i t . J . N u tr. 5 4 :2 9 3 . M cClymont, G .L . 1967. S e l e c t i v i t y and i n t a k e i n t h e . g r a z i n g r u m i n a n t . I n : C.G . Code ( E d . ) , s e c . 6 : A l i m e n t a r y c a n a l . .V ol. I . C o n tro l o f Food and W a te r I n t a k e . Handbook o f P h y s i o l o g y . Amer. P h y s i o l . S o c . Wash. D.C . M e lt o n , A .A ., J..K. R i g g s , L .A . N e ls o n an d T .C . C a r t w r i g h t . 1 9 6 7 . M ilk P r o d u c t i o n , c o m p o s i t i o n and c a l f g a i n s o f A ngus, C h a r o l a i s and H e r e f o r d cow s. J . Anim. S c i . 2 6 : 8 0 4 . 56 M i l l i g a n , L .P . and B.W. M c B rid e . 1985. S h ifts in r e q u i r e m e n t s a c r o s s p h y s i o l o g i c a l and a l i m e n t a r y . i o n pum ping by a n im a l t i s s u e s . J . N u t r . 1 1 5 :1 3 7 4 . M in so n , D .J . c o m p le x . 1981. F orage q u a l i t y : A sse ssin g P r o c . XIV I n t . G r a s s l . C o n g ., 2 3 - 2 9 . M o r r i s o n , S .R . 1 983 . Rum inant h e a t s t r e s s : e f f e c t m eans o f a l l e v i a t i o n . J . Anim. S c i . 5 7 : 1 9 8 3 . a n im a l e n e rg y E n e rg y c o s t o f th e p lan t-an im al on p r o d u c t i o n and N a t i o n a l R e s e a r c h C o u n c i l (NRC). 1984. N u tien t re q u ire m e n ts o f b e e f c a t t l e . 6 ^ r e v i s e d e d . N a t i o n a l Academy P r e s s . W a s h in g to n , D.C. N e u t z e , J . M . , F . W yler and A.M. R o u d o l f . 1968. Use o f r a d i o a c t i v e m ic ro sp h e res to a s s e s s d i s t r i b u t i o n o f c a rd ia c o u tp u t in r a b b i t s . Amer. J . P h y s i o l . 2 1 5 : 4 8 6 . N e v i l l e , W .E. a n d M. E . M c C u l l o u g h . 1969r e q u i r e m e n t s o f l a c t a t i n g and n o n l a c t a t i n g Anim. S c i . 2 9 :8 2 3 « C a lc u la te d en erg y H e re fo rd cow s. J. H o t t e r , D . L . , L.V . C u n d i f f , G.M. S m i t h , D.B. L a s t e r and K .E . G r e g o r y . 1 978. C h a ra c te riz a tio n of b io lo g ic a l ty p e s o f c a t t l e . V II. M ilk p r o d u c t i o n i n yo u n g cows a n d t r a n s m i t t e d and m a t e r n a l e f f e c t s on p r e w e a n i n g g r o w th o f p r o g e n y . J . Anim. S c i . 4 6 : 9 0 8 . N u t t , B i . G . , J.W . H ollow ay and W.T. B u t t s . c a p a c ity o f m a tu r e A ngus cows t o p e r f o r m a n c e an d f o r a g e c o n s u m p t io n 1980. R e l a t i o n s h i p o f rumen body m e a s u re m e n ts , a n im a l on p a s t u r e . J . Anim. S c i . 51: 1168. O s u ji, P .0 . 1 9 7 4 . The p h y s i o l o g y o f e a t i n g and t h e e n e r g y e x p e n d i t u r e o f th e ru m in an t a t p a s t u r e . J . Range M anage. 2 7 : 4 3 7 . R a l e i g h , R . J . , R . J . K a r t c h n e r and L .R . o x id e in range n u t r i t i o n s t u d i e s . S t a t . ' B u ll. 641. R itte n h o u se . Oregon S t a t e 1980. Chrom ic U n iv . A gr. E xp. R e e c e , W.O. 1 983 . R e s p i r a t i o n i n mammals. I n : M .J . Swenson ( E d . ) , Dukes P h y s i o l o g y o f Farm A n im a ls . T e n th e d . pp 2 2 6 - 2 5 4 . C o rn e ll U n iv . P r e s s . I t h i c a , NY. R o s i e r e , R . E . , J . D . W a lla c e and R.D . P i e p e r . 1 980. Forage in ta k e i n t w o - y e a r - o l d cows and h e i f e r s g r a z i n g b l u e gram a summer r a n g e s . J . Range M anage. 3 3 : 7 1 . R u c k e b u s c h , Y. I 98O. M o t i l i t y o f t h e r u m i n a n t s to m a c h a s s o c i a t e d w i t h s ta t e s of sle e p . I n : Y. R u c k e b u s c h a n d P . T h i v e n d s ( E d . ) , D i g e s t i v e P h y s i o l o g y and M e ta b o lis m i n R u m in a n ts , pp 7 7 - 9 0 . MTP P re ss, L an caster. 57 R u s s e l , A . J . F . and J . A . W r i g h t . 1983. F a c to r s a f f e c t i n g m ain te n a n c e r e q u i r e m e n t s o f b e e f cow s. Anim. P r o d . 37 :3 2 9 * R u t l e d g e , J . J . , O.W. R o b i n s o n , W.T. A h lschw ede and J . E . L e g a t o z . 1971. M ilk y e i l d an d i t s i n f l u e n c e on 2 0 5 - d a y w e i g h t o f b e e f c a l v e s . J. Anim. S c i . 3 3 : 5 6 3 . SAS I n s t i t u t e I n c . 198 5 . SAS U s e r ' s G u id e : S t a t i s t i c s , C a r e y , NC: SAS I n s t i t u t e I n c . , 1 9 8 5 . 584 p . 1985 E d i t i o n . S c a r n e c c h i a , D . L . , A .S . N a s t i s and J . C . M a le c h e k . 19 8 5 . f o r a g e a v a i l a b i l i t y on g r a z i n g b e h a v i o r o f h e i f e r s . M anage. 3 8 :1 7 7 * S e lf, E ffe c ts o f J . Range H.L. and G. N e ls o n 19 7 2 . S h rin k a g e d u r in g sh ip m en t o f f e e d e r c a ttle . J . Anim. S c i . 35 :4 8 9 « S e l l e r s , A .F . 1965. V o l i t i l e f a t t y a c i d p r o d u c t i o n an d r u m i n a l b l o o d flo w . In: R .W .D o u g h erty ( E d . ) , P h y s i o l o g y o f D i g e s t i o n i n t h e R u m in a n t. S m i t h , G . M . , D .B . L a s t e r , L .V . C u n d i f f and K .E . G r e g o r y . 1976. C h a ra c te riz a tio n of b io lo g ic a l ty p es o f c a t t l e . I I . P o s t w e a n in g g r o w th and f e e d e f f i c i e n c y o f s t e e r s . J . Anim. S c i . 4 3 : 3 7 . S m it h , N .E. and R .L . B a l d w i n . 1974. E f f e c t s o f b r e e d , p r e g n a n c y and l a c t a t i o n on w e i g h t o f o r g a n s a n d t i s s u e s i n d a i r y c a t t l e . J. D a iry S c i . 5 7:1055. S t o b b s , T .H . tro p ic a l 9 :1 4 1 . 1 975. F a c to rs lim itin g th e n u tr itio n a l p a s t u r e s f o r b e e f and m i l k p r o d u c t i o n . v a lu e of g razed T rop. G r a s s l. S w en so n l M .J . 1 9 8 3 . Blood c i r c u l a t i o n and t h e c a r d i o v a s c u l a r s y s t e m . I n : M .J . Swenson ( E d . ) , Dukes P h y s i o l o g y o f Farm A n im a ls . T e n t h ed. pp 1 5 - 4 0 . C o r n e l l U n iv . P r e s s , I t h i c a , NY. T a y l o r , S t . C . S . , R .B . T h e i s s e n and J . M u rra y . 1 986. In te r-b re e d r e l a t i o n s h i p o f m ain ten an ce e f f i c i e n c y to m ilk y i e l d i n c a t t l e . Anim. P r o d . 43=37. Tess, M.W., G .E . D i c k e r s o n , J . A . N i e n a b e r and C .L . F e r r e l . 1984. The e f f e c t s o f body c o m p o s i t i o n on f a s t i n g h e a t p r o d u c t i o n i n p i g s . J . Anim. S c i . 5 9 :9 9 * Thomas, V. M. 1 986. B e e f C a t t l e P r o d u c t i o n : An I n t e g r a t e d A p p r o a c h . Lea & F e b i g e r . P h i l a d e l p h i a , PA. T u l I o h , N.M. 1966a. P h y sica l s tu d ie s o f th e a lim e n ta ry t r a c t o f g raz in g c a t t l e . I I I . S easo n al changes in c a p a c ity of th e r e t i c u l o - rumen o f d a i r y c a t t l e . N.Z. J . A g r i . R e s . 9 : 2 5 2 . 58 l u l l o h , N.M. 1966b. P h y sica l s tu d ie s o f th e a lim e n ta ry t r a c t o f g razin g c a t t l e . IV . D im e n s io n s o f t h e t r a c t i n l a c t a t i n g and n o n l a c t a t i n g cow s. N .Z . J . A g r i . R e s . 9:999* U l y a t t , M .J . and R.A. B a r t o n . 1964. The e f f e c t o f body c o m p o s i t i o n and w e i g h t o f i n g e s t a on t h e n u m b ers o f la m b s r e a r e d by Romney M arsh e w e s. N a t u r e (London) 2 0 2 : 3 1 8 . U n i t e d S t a t e s D e p a r tm e n t o f A g r i c u l t u r e (USDA) - S o i l C o n s e r v a t i o n S e r v i c e (S C S ). 1976. C lim ax v e g e t a t i o n o f M o ntana: b a s e d on s o i l s and c l i m a t e . USDA-SCS. Bozeman, MT. U n i t e d S t a t e s D e p a r tm e n t Of A g r i c u l t u r e (USDA). 1975. O f f i c i a l U n ited S t a t e s s t a n d a r d s f o r g r a d e s o f c a r c a s s b e e f . USDA, Food S a f e t y and Q u a l i t y S e r v i c e , W a sh in g to n D.C . Van S o e s t , P . J . 1965. Symposium on t h e f a c t o r s i n f l u e n c i n g t h e v o l u n t a r y i n t a k e o f h e r b a g e by r u m i n a n t s : V o l u n t a r y i n t a k e i n r e l a t i o n t o c h e m i c a l c o m p o s i t i o n and d i g e s t i b i l i t y . J . Anim. S c i . 2 4 :8 3 4 . Van S o e s t , P . J . 1 983 . N u tritio n a l B ooks. C o r v a l l i s , OR. E c o lo g y of th e R u m in a n t. O&B V ercoe, J .E . 1970. The f a s t i n g m e t a b o l i s m o f B rahm an, A f r i c a n d e r and H erefo rd X S h o rth o rn c a t t l e . B r i t . J . N u t r . 24:599* V e rn o n , R.G. and M .P e a k e r . 1983* The r e g u l a t i o n o f n u t r i e n t s u p p l y w ith in th e body. I n : J . A . F . Rook a n d P . C . T hom as ( E d . ) , N u t r i t i o n a l P h y s i o l o g y o f Farm A n im a ls , pp 1 7 7 - 2 0 2 . Longman, London and New Y ork. Wade, O.L. flo w . and J .M . B i s h o p . 1962. C a rd ia c o u tp u t and r e g i o n a l b lo o d B la c k w e ll S c i e n t i f i c P u b l i c a t i o n s , O xford. W ag n er, M.W., K.M. H a v s t a d , D .E . D o o rn b o s and E .L . A y e r s 1 986. F o r a g e in ta k e o f ran g elan d b e e f c a t t l e w ith v a ry in g d e g re e s of c ro s s b re d in flu e n ce . J . Anim. S c i . 6 3 : 1 4 8 4 . W e b s t e r , A . J . F . , J.M . Brockway and J . S . S m ith . 1 974. P re d ic tio n of t h e e n e r g y r e q u i r e m e n t s f o r g r o w t h i n b e e f c a t t l e . I . The i r r e l e v a n c e o f f a s t i n g m eta b o lism . Anim. P r o d . 19=127* W e b ste r, A .J .F . 1 9 8 3 . E n e r g e t i c s o f m a i n te n a n c e an d g r o w t h . In: G i r a r d i e r and M .J . S to c k ( E d . ) , Mammalian T h e r m o g e n e s i s , pp 17 8 2 0 7 . Chapman a n d H a l l , London. W h i t e , L.M. 1 983 . Seasonal changes i n y i e l d , d i g e s t i b i l i t y p r o t e i n o f v e g e t a t i v e and f l o r a l t i l l e r s o f two g r a s s e s . M anage. 3 6 : 4 0 2 . and c r u d e J . Range 59 W i l l i a m s , C . H . , D .S . D avid and 0 . I i s m a a . 1962. The d e t e r m i n a t i o n o f c h ro m ic o x i d e i n f a e c e s s a m p l e s by a to m ic a b s o r b t i o n s p e c t r o m e t r y . J . A g r i c . S c i . 59=381. W i l l i a m s , J . H . , D .C . A n d e rs o n and D.D. K r e s s . 1979« M ilk p r o d u c t i o n in H ereford c a t t l e . I . E f f e c t s o f s e p a r a t i o n i n t e r v a l on w e i g h s u c k l e - w e ig h m i l k p r o d u c t i o n e s t i m a t e s . J . Anim. S c i . 4 9 : 1 4 3 8 . Young, B.A . w e ig h t 5 5 :6 1 9 Zak, 1975. T e m p e r a tu r e i n d u c e d c h a n g e s i n m e t a b o li s m and body of c a ttle (B o s t a u r u s ) . Can. J . P h y s i o l . P h a r m a c o l. R. 1 973. C e ll C a r d io l. 3 1 :2 1 1 . p ro life ra tio n d u rin g c a rd iac g ro w th . Am. J. 60 APPENDIX 61 T able 24. L east sq u ares a n a ly s is o f v a ria n c e o f o rg an ic m a tte r i n t a k e (OM I), 1985 Source df B io lo g ic a l ty p e OMI p e r i o d B io lo g ic a l type x OMI p e r i o d C a lf sex 4 I 4 I R eg ressio n Age o f c a l f Body w e i g h t I I MSE Mean S q u a r e s OMI (% BW/d) 1 .0 9 2 4 4 .6 9 3 4 * ” * 0 .7 1 1 0 2 .6 4 2 3 " * . 4 .0 6 4 0 " » * 0 .5 3 1 1 47 0 .5 4 8 3 R2 0 .4 3 9 1 ” ** * P < .1 0 . P < .0 5 . 01 . T ab le 2 5 . Least squares a n a ly s is o f v a ria n ce of o rg an ic m a tte r i n t a k e (O M I), 1986 Source df C a lf sex i R eg ressio n Age o f c a l f i MSE 43 R2 Mean S q u a r e s OMI '(% BW/d) ' 7 .5 7 6 2 * 9 .6 8 0 2 » « 2 .1 1 5 4 0 .1 4 6 7 ” » * P C . 10. P C .0 5 . 'I MONTANA STATE UNIVERSITY LIBRARIES