Forage intake and milk production of rangeland beef cows with varying degrees of crossbred influence
by Matthew Wayne Wagner
A thesis submitted in partial fulfillment of the requirements of the degree Cf Master of Science in
Range Science
Montana State University
© Copyright by Matthew Wayne Wagner (1985)
Abstract:
A study was conducted during the summer seasons of 1983 and 1984 to estimate the forage
consumption of free-ranging beef cows differing in milk production potential. Six lactating cows from
Hereford (HH) and 75% Simmental-25% Hereford (3S1H) breeds were used in 1983. In 1984, 3
additional breed types were evaluated: 25% Simmental-75% Hereford (1S3H), 50% Simmental-50%
Hereford (SH), and 50% Angus-50% Hereford (AH). Fecal output was estimated during June, July and
August each year using the chromic oxide dilution technique. Correction factors were derived by
comparing estimated fecal output values to actual measurements using fecal bags. Monthly forage
collections for IVOMD determinations were obtained using 4 to 6 esophageal-fistulated cows. Breed
groups did not differ significantly in body weight (P>.10) in either year. No significant difference in
average mean intake expressed as a percentage of body weight/day (%BW/d) were found between the
breeds in 1983. In 1984, significant breed group differences were detected (P<.07). Average mean
intakes for the 1S3H, HH, AH, BH, and 3S1 H were 2.2, 2.3, 2.5, 2.6 , and 2.8% BW/d respectively.
Milk production accounted for about 60% of. the variation in intake between breeds groups, but body
size and body condition differences within breeds influenced intake as well. Preliminary efficiency data
showed that 3S1H produced an average of O.98 kg milk per kg OM intake while HH produced 0.77 kg
milk. FORAGE INTAKE AND MILK PRODUCTION OF
RANGELAND BEEF COWS WITH VARYING
DEGREES OF CROSSBRED INFLUENCE
ty
Matthew Wayne Wagner
A t h e s i s s u b m itte d in p a r t i a l f u l f i l l m e n t
of th e re q u ire m e n ts of th e degree
Cf
M aster of Science
in
Range S cience
MONTANA STATE UNIVERSITY
Boz eman, Mont ana
September, 1985
APPROVAL
o f a t h e s i s su b m itted by
Matthew Wayne Wagner
T h is t h e s i s has been re a d by each member of th e t h e s i s com m ittee
and has been found to s a t i s f a c t o r y r e g a r d in g c o n te n t, E nglish usage,
fo 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 is te n c y , and i s ready
f o r su b m issio n to the C ollege of G raduate S tu d ie s .
Approval f o r th e Major Department
Date
Head, Major Department
Approved f o r the College of Graduate S tu d ie s
D ate
G ra d u a te Dean
iii
STATEMENT OF PERMISSION TO COPY
In
p re se n tin g
th is
th e sis
in
p a rtia l
f u l f i l l m e n t of th e
r e q u i r e m e n t s 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 re e t h a t th e L ib ra ry s h a l l make i t a v a i l a b l e to b o rro w ers under th e
r u l e s of th e L ib ra ry . B r i e f q u o ta tio n s from t h i s t h e s i s a r e a llo w a b le
w ith o u t s p e c ia l p e rm is sio n , pro v id ed t h a t a c c u r a te acknowledgement of
s o u rc e i s made.
P e rm is s io n f o 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 h e s i s may be g ra n te d by my major p r o f e s s o r , o r i n h i s absence, by th e
D ir e c to r of th e L i b r a r i e s when, i n t h e o p in io n of e i t h e r , th e proposed
u s e o f t h e m a t e r i a l i s f o r s c h o l a r l y p u r p o s e s . Any c o p y in g or u s e of
t h e m a t e r i a l i n t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d
w ith o u t my w r i t t e n p e rm is sio n .
iv
ACKNOWLEDGEMENTS
I
once to ld a stranger th a t I was majoring i n Range Science.
by asking me i f I was sp ec ia liz in g i n the gas or e le c tr ic kind.
He responded
Such i s the
obscurity of the science, one th a t s o l i c i t s lo g ic a l explanations from dynamic,
in te rre la te d situ a tio n s.
U n derstanding t h a t com plexity i s a l i f e lo n g
challenge, and I wish to thank those th a t helped me begin th e journey.
I am g r a t e f u l f o r th e h e lp of Kent W illia m s , whose d e te r m in a tio n i n
processing endless p ile s of fe c al samples provided r e l i e f when time was short.
For Nancy Roth, Steve Katchman, and Kathy Hanford, who aided i n data analysis
and provided s t a t i s t i c a l assistance.
H e artfelt appreciation goes out to Web
and Charlotte lhackeray fo r th e ir overwhelming graciousness, who made seemingly
impossible task s a pleasurable experience.
I wish to thank Dan Doornbos and
Don Anderson fo r providing the c a t t l e w ith which we conducted our research, yet
gave me the re s p o n s ib ility to d ire c t th e experiment.
For my i n i t i a t i o n in to
the f i e l d of Range N utrition, I want to remember Eldon Ayers.
His enthusiasm
was a driving force helping me deal with adverse situ a tio n s.
To my partner,
W ill Lathrop I can't express enough g ratitu d e.
proved invaluable to the study.
learned from him.
His hard work and cow sense
I w i l l always remember Will and th e things I
I want to express my indebtedness to my good frien d and
counselor, Kris Havstad.
Kris was th e kind of teacher th a t could explain a
confusing problem or technical rid d le without words.
He ta u g it with actions,
i l l u s t r a t i o n s , or questions th a t allowed you to comprehend on your own.
I have
never known anyone to work with such enthusiasm and dedication, in te n t on being
th a t "cutting edge" but always l e t t i n g h is students do the "cutting".
To my lovely wife Kathy, I dedicate t h i s manuscript.
In many ways she
provided support i n the f i e l d , laboratory, and a t home lending advice which I
learned to cherish, and dedication which I long to emulate.
V
TABLE OF CONTENTS
L IS T
OF TABLES................................................
Page
vi
ABSTRACT............... ............................................................................................................ ..
INTRODUCTION....................................
1
LITERATURE REVIEW.........................................................................................................
3
I n t r o d u c t i o n .........................................................................................................
F a c to r s I n f lu e n c in g Forage In ta k e by Grazing R u m in an ts.. . . . . .
P h y s ic a l L i m i t a t i o n s .......................................................................................
P h y s io lo g ic a l S ta g e .........................................................................................
Forage F a c t o r s ............................... ....................................................................
Environmental F a c t o r s ...................................................................
P r o d u c tiv e E f fic ie n c y of Free-R anging Cows Varying i n
B io lo g ic a l P o t e n t i a l .......................................................................................
P rev io u s In ta k e E s tim a te s Using Chromic O xide...................................
3
3
6
8
14
18
21
24
MATERIALS AND METHODS................................................................................................
25
RESULTS..............................................................................................................................
28
In ta k e D iff e re n c e s AmongBreeds - 1983 T r i a l .....................................
1984 T r i a l .............................................................................................................
Milk P ro d u c tio n ..................................................................................
Body Measurements.............................................................................................
Forage D i g e s t i b i l i t y .......................... ..........................■..................................
■ Comparison of Fecal Output E s tim a te s Using the Chromic Oxide
and T o ta l C o lle c ti o n Methods............................................................. ; . . .
28
28
30
30
32
DISCUSSION............................................................................
33
34
F a c to r s A ffe c tin g In ta k e D iff e re n c e s W ithin and Between
B r e e d s ..................................................................................................................... 34
■ Forage D i g e s t i b i l i t y and I n t a k e .................................................................
37
P re lim in a ry E f fic ie n c y E v a lu a tio n s ................................. ....................... ' 40
SUMMARY......................................................................................................................
42
LITERATURE CITED...........................................................................................................
44
APPENDIX
52
vi
LIST OF TABLES
TabI e
Page
1
1983 D aily fo ra g e in t a k e f o r l a c t a t i n g cows.......................
29
2
1984 D aily f o r a g e i n t a k e f o r f i v e cow b r e e d s ............................
29
3
1984 Average d a i l y m ilk p ro d u c tio n f o r f i v e cow b r e e d s . . .
31
4
Body w eig h t and w e ig h t! h e ig h t r a t i o s f o r b reed s used i n
1983 and 1984......... .............. .....................................................................
31
5
Monthly fo ra g e IVOMD f o r two y e a r s ..........................................
33
6
Average d a i l y in ta k e f o r two b reeds over both f i e l d
s e a s o n s .............................................................................................................
37
Appendix Tables
7
8
9
In ta k e v a lu e s f o r v a rio u s b re e d s of g ra z in g cows u sin g
chromic oxide method f o r f e c a l o u t p u t ............................................
L e a st s q u a re s a n a l y s i s of v a r ia n c e of o rg a n ic m a tte r
in ta k e 1983 ............................................................................................
L east s q au res a n a l y s i s of v a r ia n c e of body w eight 1 9 8 3 ...
10
L east sq u ares a n a l y s i s o f v a ria n c e of o rganic m a tte r
i n t a k e 1984............................................................
11
L east s q u ares a n a l y s i s of v a ria n c e of m ilk p ro d u c tio n
1984 ...........................................................................
12
L east s q u ares a n a l y s i s of v a r ia n c e of body weight and
w eight ! h e ig h t r a t i o 1984............................................
13
14
15
16
53
54
54
56
Comparison of OMD between s e l e c t e d samples o f e x tr u s a
u s in g two d ry in g m ethods........................................................
57
1983 F ecal ou tp u t e s tim a te s f o r dry cows u sin g t o t a l
c o l l e c t i o n and chromic oxide t e c h n i q u e s ...................................
Least s q au res a n a l y s i s of v a r ia n c e of o rg an ic m a tte r
i n t a k e f o r HH and 3SIH b reed s 1983 and 1984.............................
In ta k e d i f f e r e n c e s and e f f i c i e n c y e v a lu a tio n s f o r breeds
used i n 1984...................................................................................................
58
59
60
v ii
LIST OF TABLES - Continued
T able
17
Page
L e a st s q u a re s a n a l y s i s of v a r ia n c e o f _in v i t r o o rg a n ic
m a tte r d i g e s t i b i l i t y ........... ...................................................................
61
v iii
ABSTRACT
A study was conducted d u rin g t h e summer seasons o f 1983 and 1984
t o e s t i m a t e th e fo ra g e consumption of f r e e - r a n g i n g beef 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 p o t e n t i a l . S i x l a c t a t i n g cows fro m H e r e f o r d (HH)
and 75% S i m m e n t a l - 25% H e r e f o r d ( 3 S1 H) b r e e d s w e re u s e d i n 1983. I n
1984, 3 a d d i t i o n a l b r e e d t y p e s w e r e e v a l u a t e d : 25% S im m e n ta l- Y 5%
H e r e f o r d (1S3H ), 50% Sim m en tal-5 0 % H e r e f o r d (SH), and 50% Angus-50%
H erefo rd (AH). Fecal outp u t was e s t i m a t e d d u rin g June, J u ly and August
e a c h y e a r u s i n g th e c h r o m ic o x id e d i l u t i o n t e c h n i q u e . C o r r e c t i o n
f a c t o r s w e re d e r i v e d by c o m p a r in g e s t i m a t e d f e c a l o u t p u t v a l u e s t o
a c t u a l m easurements u sin g f e c a l bags. Monthly fo ra g e c o l l e c t i o n s f o r
IVOMD d e te r m in a tio n s w ere o b ta in e d u s in g 4 to 6 e s o p h a g e a l - f i s t u la te d
cows. Breed groups d id not d i f f e r s i g n i f i c a n t l y i n body w eight (PXIO)
i n e i t h e r y e a r . No s i g n i f i c a n t d i f f e r e n c e i n a v e r a g e mean i n t a k e
e x p r e s s e d a s a p e r c e n t a g e o f body w e i g h t / d a y (%BW/d) w e re fo u n d
b e tw e e n t h e b r e e d s i n 19 83. I n 1 984, s i g n i f i c a n t b r e e d group
d i f f e r e n c e s were d e te c te d (P<.07). Average mean i n t a k e s f o r th e 1S3H,
HH, AH, BH, a n d 3S1H w e r e 2 . 2 , 2 . 3 , 2 . 5 , 2.6 , a n d 2.8% BW/d
r e s p e c t i v e l y . Milk p ro d u c tio n acco u n ted f o r ab o u t 60% of. th e v a r i a t i o n
i n i n t a k e b e tw e e n b r e e d s g r o u p s , b u t body s i z e and body c o n d i t i o n
d if f e r e n c e s w ith in b reed s in flu e n c e d in ta k e a s w e ll. P re lim in a ry
e f f i c i e n c y d a ta showed t h a t 3S1H produced an average of O.98 kg m ilk
per kg OM i n t a k e w h ile HH produced 0.77 kg milk.
I
INTRODUCTION
To e f f e c t i v e l y
p ro d u c tio n ,
it
m anage r a n g e la n d s f o r
is
necessary
to
have
c o n s u m p tio n by t h e g r a z i n g a n i m a l .
y e a r ly dry
o p tim u m l i v e s t o c k
k n o w le d g e
of
th e
forage
Van Dyne (I 9 6 0 ) e s t i m a t e d th e
m a tte r in ta k e from d a ta sum m arizing 31 s t u d i e s o f g ra z in g
c a t t l e t o be a b o u t 1.8% body w e i g h t / d a y (%BW/d). W ith t h e i n c r e a s e d
use
of h e a v ie r m ature w e ig h t,
th e re
may
be
a
need
to
high m ilk -p ro d u c in g b reed s o f
a d ju st
s to c k in g
ra te s
based
c a ttle ,
on fo ra g e
consumption e s t i m a t e s .
When a b u n d a n t , good q u a l i t y f o r a g e i s a v a i l a b l e , t h e v o l u n t a r y
i n t a k e o f g r a z i n g r u m i n a n t s i s i n f l u e n c e d by e n e r g y demand (A rn o ld ,
1 97 0 ).
The e n e r g y
b a lan c e
of
an a n i m a l
is
d e term in e d
by t h e
d i f f e r e n c e b e tw e e n e n e r g y i n p u t ( f e e d ) a n d t h e e n e r g y e x p e n d e d f o r
m aintenance,
1970).
m ilk p ro d u c tio n ,
re p ro d u c tio n and a c t i v i t y ( Braumg a r d t,
Because of the bulky and f i b r o u s n a tu re of most range fo r a g e s ,
t h e p h y s i c a l l i m i t a t i o n o f i n t a k e due t o g u t f i l l u s u a l l y o c c u r s
before
energy
s a tie ty
(C a m p lin g , 1970). The p o i n t w h e re p h y s i c a l
d i s t e n t i o n of th e rumen l i m i t s i n t a k e and m e ta b o lic s i g n a l s begin to
dom inate i s b e lie v e d to be when fo ra g e d i g e s t i b i l i t y i s a p p ro x im a te ly
62
- 70%
(Conrad e t
a l.,
1964; McClymont,
B r a u m g a r d t , 1 965), h o w e v e r t h i s
s ta g e
of
p ro d u c tio n
1967; Montgomery
and
r a n g e may v a r y w i t h body s i z e and
(Conrad e t a l . ,
1964).
I f p h y s ic a l c o n d itio n s
l i m i t in t a k e on low q u a l i t y fo r a g e s , th e n rumen c a p a c ity , f e r m e n ta tio n
and
passage r a t e
o f f o r a g e w o u ld d e t e r m i n e t h e am ount o f f e e d an
a n i m a l c o u l d i n g e s t . W h ile i t i s t r u e t h a t t h e m ain d e t e r m i n a n t of
ru m en c a p a c i t y
is
t h e s i z e of t h e a n im a l' (N u tt e t a l . , I 9 80;
Van
2
S o e s t 1982), c h a n g e s i n r u m i n a l v o lu m e a r e n o t n e c e s s a r i l y e q u a l t o
c h a n g e s i n body w e i g h t . B in e s (1971) s t a t e d t h a t i n t a k e i s b r o a d l y
r e l a t e d t o th e l iv e w e i g h t of th e a n im a l, which i s a l s o r e l a t e d t o th e
siz e
o f t h e ■ a b d o m in a l
c a v ity .
R u m in a l
documented i n l a c t a t i n g ewes ( F e ll e t a l . ,
a n d B a l d w i n , 1974; T u l l o h ,
h y p e r t r o p h y h a s b een
1964) and d a ir y cows (Smith
1 966) a n d may a l s o i m p a c t t h e d i g e s t i v e
c a p a c ity of ru m in an ts v a ry in g i n p ro d u c tio n .
If
ru m in a n ts
c o n c e n tra tio n ,
consum e f o r a g e s
of h ig h
d ig e stib le
energy
t h e n m e t a b o l i c s i g n a l s a s s o c i a t e d w i t h t h e e n e rg y
b a l a n c e o f a n a n i m a l may r e g u l a t e f o o d i n t a k e (B in e s , I 971).
Under
th e s e c o n d itio n s , breed d i f f e r e n c e s i n l e v e l of m ilk p ro d u c tio n could
cause f o r a g e i n t a k e d i f f e r e n c e s .
R e s e a r c h w as i n i t i a t e d i n 1981 a t t h e N o r t h e r n A g r i c u l t u r a l
Research C enter, l o c a t e d n e a r Havre, Montana to d e te rm in e th e r e l a t i v e
e f f i c i e n c y o f g r a z e d f o r a g e consum ed by f i v e b e e f cow b r e e d s . T h is
s t u d y was
c o n d u c te d
d u rin g
th e
su m m ers
o f 1983 and 1984 to ( I )
e s t i m a t e t h e d a i l y f o r a g e o r g a n i c m a t t e r i n t a k e o f f i v e b eefcow
b re e d s d i f f e r i n g i n m ilk p ro d u c tio n p o t e n t i a l ,
and
( 2)
p ro v id e
in f o r m a t io n n e c e s sa ry to a s s e s s t h e r e l a t i v e p ro d u c tio n e f f i c i e n c y of
each b reed type on n a t i v e r a n g e la n d s .
3
LITERATURE REVIEW
I n tr o d u c ti o n
When g ra z in g c a t t l e of d i f f e r e n t g e n e ti c p o t e n t i a l s f o r dam and
o f f s p r i n g p e r f o r m a n c e a r e d e r i v i n g n u t r i e n t s fro m t h e same f o r a g e
base,
th e
in te ra c tio n
b e tw e e n e n e r g e t i c
demand a n d s u b s e q u e n t
p r o d u c t i v i t y may d e te rm in e t h e i r dry m a t t e r in ta k e .
M etab o lic energy
demand i s a f u n c t i o n o f s e v e r a l f a c t o r s i n c l u d i n g t h e m a i n t e n a n c e
re q u ire m e n t of an an im a l.
Maintenance demands may be in c r e a s e d from
40 to 60% ( Havstad and Malachek, 1982) f o r c a t t l e g ra z in g ra n g e la n d a s
com pared w ith
c o n fin e d s i t u a t i o n s .
. T here a r e v a r i a t i o n s i n
m aintenance r e q u ire m e n ts based on b re e d s and p h y s io lo g ic a l age a s w e ll
(NRC, 1984).
In o rd e r to u l t i m a t e l y i d e n t i f y th e p ro d u c tiv e p o t e n t i a l
and a d a p t i b i l i t y
of v a rio u s
b reed s
to
a p a rtic u la r
g ra z in g
en v iro n m en t, i t i s n e c e s sa ry t o e s t i m a t e t h e i r fo r a g e consumption.
b rie f
rev ie w
of
th e f a c to r s
in flu e n c in g
th e in ta k e
A
of g ra z in g
ru m in a n ts w i l l h e lp e l u c i d a t e a complex and i n t e r a c t i v e s y s te m .
F a c to rs I n f lu e n c in g Forge In ta k e bv Grazing Ruminants
T h e re i s
a v a st array
b e h av io r of g ra z in g ru m in a n ts .
of s t i m u l i
th a t a ffe c t
th e fo ra g in g
In a d d i t i o n , th e ra n g e la n d environm ent
a n d i t s d i v e r s i t y s e r v e s t o add t o t h e c o m p l e x i t y o f t h e a n i m a l ’s
n u t r i t i o n a l e c o lo g y . To e x p l a i n t h e i m p a c t o f t h e v a r i a b l e s d r i v i n g
v o lu n ta r y f o r a g e i n t a k e ,
th r e e c r i t e r i a must be e v a lu a te d .
(I)
in h e re n t
in ta k e
re g u la tio n
c h a ra c te ristic s,
to
th e
a n im a l,
They a r e :
( 2) f o r a g e
base
and ( 3 ) e n v i r o n m e n t a l f a c t o r s . T h e se i n f l u e n c e s
4
combine t o form a dynamic model, one i n which a change i n one elem ent
d e n o tes a change somewhere e l s e i n th e scheme.
I n n a te r e g u l a t o r y mechanisms a r e c o n t r o l l e d by m e ta b o lic b alance,
p h y s ic a l l i m i t a t i o n s and th e p h y s io lo g ic a l s t a t e of th e an im al.
. McClymont
( 1967)
sta te s
th a t
th e
o n ly
in trin sic
stim u lu s
f a c i l i t a t i n g phagic b e h a v io r i n th e g ra z in g ru m in an t i s t o t a l energy
demand.
T h is demand i s a s u m m a tio n o f t h e e n e r g y r e q u i r e d f o r
m a in te n an c e ,
g r o w th ,
g e sta tio n ,
e n v iro n m e n ta l s t r e s s e s .
m ilk
p ro d u c tio n ,
e x e rc ise
and
When s h o r t te r m demand e x c e e d s m e t a b o l i c
energy a v a i l a b l e to th e a n im a l, fe e d in g b eg in s.
beyond t h e l e v e l re q u ire d ,
As energy i s s u p p lie d
fe e d in g w i l l cease ( B la x te r,
1962; Forbes,
1980). T his energy b a lan c e may be governed by th e hypothalam us, which
" s e n s e s " v a r i o u s f e e d b a c k s i g n a l s su c h a s d i s t e n t i o n s t i m u l i and
changes i n m e ta b o lite
c o n c e n tra tio n .
in c re a se s,
energy
d ig e stib le
As f o r a g e
c o n c e n tra tio n
d ig e stib ility
in c re a se s,
and t h e
r e g u l a t i o n of food i n t a k e becomes m e ta b o lic i n n a tu re (B in es,
1971).
This l e v e l of d i g e s t i b l e energy i s b e lie v e d t o be a t th e p o in t where
forage 'd i g e s t i b i l i t y
r e a c h e s a b o u t 62 - 70%.
Below
th is
le v e l,
p h y s i c a l d i s t e n t i o n o f t h e ru m en l i m i t s i n t a k e ; a b o v e i t ,
e n e rg y
i n t a k e b eco m es t h e o v e r i d i n g f a c t o r i n h i b i t i n g f o r a g e c o n s u m p tio n
(McClymont,
1957).
Conrad e t a l . (1964) concluded from t h e i r r e s u l t s
w ith l a c t a t i n g d a iry cows t h a t th e p o in t where p h y s ic a l l i m i t a t i o n s on
e a t i n g c ea se and m e ta b o lic i n f l u e n c e s dom inate v a r i e s w ith body s i z e
and p ro d u c tio n . Montgomery and B ra u m g a r d t ( 1 965a) r e p o r t e d t h a t f o r
d a ir y h e i f e r s consuming r a t i o n s o f i n c r e a s i n g dry m a tte r d i g e s t i b i l i t y
(DMD), i n t a k e d ecrea se d a s a r e s u l t of energy s a t i e t y .
Conrad e t a l .
5
(1964) found t h a t w ith h igh-roughage r a t i o n s between 67 and 80% DMD,
i n t a k e d e c re a se d w ith i n c r e a s i n g d i g e s t i b i l i t y .
In c o n t r a s t ,
in ta k e s
w e re l o w e r f o r cows c o n su m in g r a t i o n s below 6 0% DMD due t o g u t f i l l
(Montgomery and Baumgardt, 1965b).
The m ajor su sp e c te d chem ical feedback s i g n a l s r e g u l a t i n g energy
i n t a k e by ru m in a n ts i n c lu d e v o l a t i l e f a t t y a c id (VFA) c o n c e n tr a ta tio n ,
rum en pH, and h o rm o n a l s e c r e t i o n .
Among t h e p r o d u c t s o f d i g e s t i o n ,
p ro p r io n a te p la y s a s i m i l a r r o l e i n c o n t r o l l i n g th e food in ta k e of
ru m in a n ts much a s g lu co se i s th o u g h t to do i n m o n o g a stric a n im a ls , by
a c t i n g a s a n i n d e x o f t h e r a t e o f a b s o r p t i o n o f a l l VFA’s ( F o r b e s ,
I 9 8 0 ).
P r o p r i o n a t e i s s e n s e d by t h e p o r t a l v e i n a n d c o n c e n t r a t i o n
s i g n a l s a r e t r a n s f e r r e d v i a t h e v a g a s n e r v e t o t h e h y p o th a la m u s .
Ruminal a c e t a t e c o n c e n tr a tio n h as been found t o p lay a c e n t r a l r o l e i n
c o n t r o l l i n g m e a l s i z e on r a n g e f o r a g e s i n p a r t i c u l a r (W aldo, I 969).
I t h a s been s u g g este d t h a t t h e r e a r e r e c e p t o r s s e n s i t i v e to a c e t a t e on
th e lumen s id e of th e rumen ( B a ile and F o rb es, 1974).
B a i l e and F o r b e s (1974) s t a t e t h a t t h e r e i s no e v i d e n c e t h a t
g r o w th ho rm o n e (GH) i s a f e e d b a c k s i g n a l f o r e n e r g y b a l a n c e u n d e r
normal c o n d itio n s , but Forbes (1980) r e p o r t e d
th a t
a low i n s u l i n : GH
r a t i o s t i m u l a t e s l i p o l y s i s and might be ex p ected to o ccu r around th e
t i m e o f m e al i n i t i a t i o n .
He s u g g e s t e d a l i n k b e tw e e n a d e f i c i t o f
energy - y i e l d i n g m e t a b o l i t e s ( c o r r e l a t e d by an in c r e a s e d s e c r e t i o n of
GH) a n d t h e o n s e t o f f e e d i n g .
E stro g e n s a re b e lie v e d to d e p re ss
i n t a k e d u r i n g e s t r u s a n d i n l a t e p r e g n a n c y ( B a i l e and F o r b e s , 1974),
b u t w h e t h e r t h i s i s a n i n d i r e c t o r c e n t r a l a c t i o n on t h e s a t i e t y
c e n t e r i s n o t known.
B a lc h and C am p lin g ( 1 962) s t r e s s e d t h a t t h e
6
ch a n g e s i n fo o d in t a k e a s s o c i a t e d w ith horm one b a la n c e may be r e l a t e d
to ch an g e s i n in d u c e d m e ta b o lism .
T h e re a r e
tw o w ays t h a t a d i p o s e t i s s u e
h o m e o s ta tic b a lan c e o f energy i n th e ru m in a n t.
c o n trib u te s to
th e
F i r s t , th e r a te a t
which ad ip o se t i s s u e can s y n th e s iz e t r i g l y c e r i d e s seems t o be l i m i t e d .
As t h i s l i m i t i s approached, r e c e p t o r s s e n s i t i v e t o e x c e s s energy w i l l
te n d t o d e p re ss in ta k e .
Secondly, i t h a s been proposed t h a t "leakage"
of f a t t y a c i d s from a d ip o se c e l l s i s p o s i t i v e l y r e l a t e d to t h e i r s iz e .
The f a t t e r t h e a n i m a l t h e s t r o n g e r t h e f e e d b a c k s i g n a l on e n e r g y
a v a i l a b i l i t y (F o rb e s, I9 6 0 ).
The r a p i d f e r m e n ta tio n of im m ature f o r a g e s may produce s u f f i c i e n t
a c i d to cause a drop i n rumen pH which d e la y s c e l l u l o l y t i c d i g e s t i o n
o f f o r a g e c e l l w a l l s , t h u s d e p r e s s i n g i n t a k e (Van S o e s t , 1982). I n
Jones* ( I 972) r e v i e w . o f t h e c h e m i c a l c o n t r o l o f f e e d i n t a k e , i t was
d eterm in ed t h a t a drop i n pH f a c i l i t a t e s t h e a b s o r p tio n of VFA a c r o s s
t h e rumen e p ith e liu m , a llo w in g th e a c t i v a t i o n p o i n t o f t h e r e c e p t o r
s ig n a l t o be accom plished w ith lo w e r i n t a k e s .
B a ile and Forbes (1974)
s t a t e d t h a t fe e d i n t a k e i s l i k e l y d e p re sse d when rumen f l u i d pH f a l l s
b elo w 5.5 because of th e r e s u l t i n g rumen s t a s i s .
P h y s ic a l L im ita tio n s
P h y s i c a l b u lk o f l e s s d i g e s t i b l e f o r a g e s a n d c a p a c i t y o f t h e
ru m in an t g a s t r o i n t e s t i n a l t r a c t a r e dom inant f a c t o r s l i m i t i n g fo ra g e
i n t a k e by ru m in a n ts ( E l l i s ,
1978). P h y s ic a l r e g u l a t i o n o f food in ta k e
i n v o l v e s s t r e t c h r e c e p t o r s i n t h e ru m en w a l l ,
b u t t h e n a t u r e and
p r e c i s e l o c a t i o n of th e s e i s n o t y e t known (Bines, 1971).
While i t i s
I
t r u e t h a t t h e m a in d e t e r m i n a n t o f rum en c a p a c i t y i s t h e s i z e o f t h e
a n im a l, changes i n ru m in a l volume a r e n o t n e c e s s a r i l y equal to changes
i n body w e i g h t .
In ta k e i s b ro a d ly r e l a t e d to th e l i v e w e ig h t o f th e
an im al and i s d eterm in ed by th e s i z e of th e abdominal c a v i t y (B ines,
1971)
and
by t h e
re tic u lo ru m e n .
ra te
of
d isa p p e a ra n c e
of d ig e s ta
from
th e
The r a t e o f d i s a p p e a r a n c e d e p e n d s on t h e r a t e o f
breakdown i n t h e r e tic u lo r u m e n by m ic ro b ia l and m echanical p ro c e s s e s
(Campling, 1970).
Nutt e t a l .
(1980) found no r e l a t i o n s h i p between rumen c a p a c ity
and DM d i g e s t i b i l i t y o f f e s c u e - legume and fe s c u e p a s t u r e s alth o u g h
o t h e r r e s e a r c h e r s f o u n d t h a t a s ru m en v o lu m e i n c r e a s e d , f o r a g e DM
d i g e s t i b i l i t y i n c r e a s e d ( P u r s e r a n d M o ir, 1 966).
N u tt e t a l . (1980)
f o u n d t h a t s t r u c t u r a l l y l a r g e cows h a d l a r g e r ru m en c a p a c i t i e s and
g r e a t e r i n t a k e s th a n s t r u c t u r a l l y sm a ll cows.
As a p e rc en ta g e of body
w e i g h t h o w e v e r, rum en c a p a c i t y was n o t r e l a t e d t o s t r u c t u r a l s i z e
r e f l e c t i n g d i f f e r e n c e s i n body co m p o sitio n of the cows examined.
y i e l d w as a l s o n o n - r e l a t e d t o ru m en c a p a c i t y .
Milk
One way o f r e l a t i n g
i n t a k e to cows of- d i f f e r e n t s i z e s i s t o e x p re ss body s i z e i n te rm s of
m e ta b o lic body w eig h t (MBW).
M etab o lic body w eight d e s c r ib e s s u rfa c e
a r e a a n d t h e r e f o r e m a i n t e n a n c e r e q u i r e m e n t s (K othm ann, 197 8).
The
fe e d re q u ire m e n t f o r m aintenance becomes p r o p o r tio n a l to th e a n im a l’s
MBW when i n t a k e i s r e g u l a t e d by c h e m o s t a t i c m e c h a n is m s .
It is
q u e s t i o n a b l e w h e t h e r any s i n g l e e x p r e s s i o n o f l i v e w e i g h t can be
a d o p te d f o r a n im a ls of a l l a g e s and l i v e w e ig h ts .
The r e l a t i o n s h i p
between i n t a k e and body s i z e changes m arkedly a t w e ig h ts lo w e r th an
8
400 l b s
sin ce
t h e ru m en d e v e l o p s m o re r a p i d l y t h a n t h e o v e r a l l
developm ent of th e body (Holmes e t a l . , 1961).
The am ount o f body f a t a l s o h a s a n e f f e c t on a b d o m in a l s p a c e i n
t h e ru m in a n t.
w e ig h t,
When rumen c a p a c ity was e x p re sse d i n p r o p o r tio n to body
f a t t e r cows had s i g n i f i c a n t l y s m a l l e r rumen c a p a c i t i e s th a n
d i d t h i n n e r cows ( N u t t e t a l . ,
1980).
I n v e r s e r e l a t i o n s b e tw e e n
w e i g h t o f i n t e r n a l f a t and w e i g h t o f g u t c o n t e n t s w e re r e p o r t e d by
B a lc h a n d C am p lin g (1 9 6 2 ).
B in e s
(1971)
sta te s
th a t
e x te n siv e
d e p o s i t i o n o f f a t w i t h i n t h e a b d o m in a l c a v i t y a p p a r e n t l y r e d u c e s
d i g e s t i v e c a p a c ity and t h e r e f o r e roughage in t a k e .
He concluded t h a t
s i n c e f a t cows d id n o t e a t enough hay t o m a i n t a i n w e i g h t , and t h i n
cows a t e enough o f t h e same hay t o g a i n w e i g h t , t h e e x i s t e n c e o f a
p h y s ic a l r e g u l a t o r a p p e a rs l i k e l y .
P h y s io lo g ic a l Stage
A n o th e r m a jo r
d eterm in a n t
th e fo rag e in ta k e
of g ra z in g
ru m in a n ts i s th e p h y s i o l o g i c a l c o n d i t i o n o f t h e a n i m a l .
L a c tatio n ,
p re g n a n c y and g ro w th c o n t r i b u t e
of
to in c re a s e
su bsequent need f o r a d d i t i o n a l fe e d in t a k e .
cost
d e m an d in g t h r e e
e n e r g y demands and
L a c t a t i o n i s an e n e r g e t i c
tim e s th e m ain te n an c e re q u ir e m e n t i n h ig h
p r o d u c i n g d a i r y cows ( B a i l e and F o r b e s , I 974).
J o u r n e t and Remond
(1976) o b s e r v e d t h a t t h e DM i n t a k e o f r o u g h a g e s i n c r e a s e d by 2 k g /d
d u rin g th e f i r s t e ig h t weeks o f l a c t a t i o n and d id n o t depend g r e a t l y
on t h e l e v e l of roughage in ta k e b e fo re c a lv in g .
Johnson e t a l . (1966)
n o t i c e d t h a t H o l s t e i n cows i n c r e a s e d t h e i r DM hay i n t a k e 50% d u r i n g
t h e f i r s t o n e - t h i r d o f l a c t a t i o n , p e a k i n g by t h e 17t h w eek.
In ta k e
9
d iffe re n c e s
av erag in g
about
50% w e re o b s e r v e d
b e tw e e n d ry
and
l a c t a t i n g t w i n J e r s e y c r o s s b r e d c a t t l e , a l t h o u g h p eak g r o s s e n e r g y
i n t a k e w as n o t o b t a i n e d d u r i n g p e a k m i l k y i e l d , b u t 15 weeks l a t e r .
T h is t i m e l a g may r e p r e s e n t a p e r i o d f o r r e p l e t i o n o f body r e s e r v e s
u s e d i n e a r l y l a c t a t i o n ( H u tto n , 1 9 6 3 ).
stated
I n c o n t r a s t , F o r b e s (1971)
t h a t food i n t a k e r e a c h e s a peak a b o u t th e
la c ta tio n .
s i x t h week o f
He s u g g e s ts t h a t th e e x p u lsio n s of th e f e t u s im m e d ia te ly
g iv e s ample room f o r rumen expansion,
so th e tim e l a g i s most l i k e l y
n o t d e p e n d a n t on a n i n c r e a s e i n d i g e s t i v e c a p a c ity .
An i n t e r e s t i n g a d a p t a t i o n to th e energy demands o f l a c t a t i o n i s
an
in c re a s e d
d ig e stiv e
c a p a c ity
r e tic u lo r u m e n and i n t e s t i n e s .
due
to
h y p e rtro p h y
of
th e
An a d a p t a t i o n of t h i s k in d would e n ab le
a l a c t a t i n g cow to m a in ta in a g r e a t e r i n t a k e w ith o u t changing th e r a t e
of passage or th e d i g e s t i b i l i t y of th e d i e t (T u llo h ,
1966).
The f i r s t
r e p o r t co n cern in g h y p e rtro p h y d e s c rib e d t h e h i s t o l o g i c a l , chem ical and
p h y s ic a l changes o c c u rin g i n t h e a l i m e n t a r y c a n a l o f l a c t a t i n g r a t s
( F e l l e t a l . , 1 9 6 3 ).
They o b s e r v e d t h a t t h e p a r i e t a l c e l l s i n t h e
stomach o f l a c t a t i n g a n im a ls became h y p e rtro p h ie d , and by th e 16th day
of la c ta tio n ,
th e t o t a l
n i t r o g e n c o n t e n t o f t h e s to m a c h ,
sm all
i n t e s t i n e and caecum had i n c r e a s e d an av erage o f 65% over t h a t of th e
c o n tro ls.
I n a d d i t i o n , t h e a v e r a g e w e i g h t o f t h e s to m a c h w as 50%
g r e a t e r th a n t h a t of n o n - l a c t a t i n g r a t s .
B ut t h e m o st s t r i k i n g
f e a t u r e of th e h y p e rtro p h y was an i n c r e a s e i n th e h e i g h t and th ic k n e s s
of th e i n t e s t i n a l v i l l i .
I t was su g g e s te d t h a t th e r e s u l t s were due
t o an a d a p t i v e r e s p o n s e o f t h e i n t e s t i n a l mucosa t o t h e i n c r e a s e d
10
energy demands o f l a c t a t i o n r a t h e r th a n t h e d i r e c t e f f e c t o f p h y s ic a l
d i s t e n t i o n due t o in c r e a s e d food i n t a k e .
A s i m i l a r s tu d y p e r f o r m e d by F e l l e t a l . (1964) show ed many o f
th e same r e s u l t s i n l a c t a t i n g ewes.
There was a d e f i n i t e en larg em e n t
of th e a lim e n ta r y canal i n d i c a t e d by w e ig h t, t o t a l n i t r o g e n g a in s and
h i s t o l o g i c a l com parisons t o n o n - l a c t a t i n g c o n t r o l s .
H y p e r tr o p h y o f
r u m i n a l m ucosa h a s a l s o b e en c o n f i r m e d by F e l l e t a l . (1972) and
Weekes (1 9 7 1 ).
W eig h t i n c r e a s e s w e re f o u n d t o o c c u r i n t h e r u m i n a l
mucosa, abomasum and s m a ll i n t e s t i n e of l a c t a t i n g cows f e d a r a t i o n of
a p p ro x im a te ly 70% dry m a tte r d i g e s t i b i l i t y (DMD).
Weekes (1971) found
t h a t i n c o n j u n c t i o n w i t h i n c r e a s i n g ru m en m u c o sa l w e i g h t , enzyme
a c t i v i t i e s and i n v i t r o l a c t a t e p ro d u c tio n p er rumen a l s o in c re a s e d .
I t w as t h o u g h t t h a t t h i s c o u l d i n c r e a s e t h e s u p p ly o f s u b s t r a t e f o r
g lu c o n e o g e n e s i s d u r i n g l a c t a t i o n .
Cambell,
An a s s o c i a t e d s t u d y (Moon and
1973) r e v e a le d t h a t h y p e r tr o p h ic changes i n t h e rumen w a ll
were, combined w ith an i n c r e a s e i n th e s i z e of i n d i v i d u a l p a p i l l i and a
re g re ss io n of a h y p e rk e ra to tic c o n d itio n .
Peak ru m en w e i g h t w as
re a ch e d a t ab o u t 20 days o f l a c t a t i o n , when th e lam bs w ere weaned.
It
was concluded t h a t h y p e rtro p h y of th e ru m in a l mucosa i s due p a r t i a l l y
to in c re a s e d c e ll d iv is io n .
Peak v a l u e s o f DNA a n d RNA o c c u r r e d
a p p ro x im a te ly a t th e tim e when c e l l d i v i s i o n was g r e a t e s t .
RNA was
used a s an in d e x to p r o t e i n s y n t h e s i s and may r e f l e c t growth p ro c e s s e s
i n th e c e l l .
Smith and Baldwin (1974) used m a tu re d a iry cows t o d e term in e t h e
e f f e c t s of pregnancy and l a c t a t i o n on th e w e ig h ts of g a s t r o i n t e s t i n a l
t r a c t o rg an s and t i s s u e s .
They s t a t e t h a t alth o u g h organ w e ig h t i s a
11
f u n c t i o n o f body w e i g h t , r e l a t i v e c h a n g e s i n o r g a n w e i g h t s a r e n o t
e q u i v a l e n t t o r e l a t i v e c h a n g e s i n body w e i g h t .
Log—Log r e g r e s s i o n
a n a l y s i s was used t o a llo w com parisons o f t i s s u e s and org an s between
n o n - l a c t a t i n g a n d l a c t a t i n g c a t t l e on a common body w e i g h t b a s i s .
W eights o f th e g a s t r o i n t e s t i n a l organs f o r n o n - l a c t a t i n g and l a c t a t i n g
c o w s w e r e 3 .7 5 a n d 4.85% o f t o t a l
body w e ig h t r e s p e c t i v e l y ,
r e p r e s e n t i n g a 30% i n c r e a s e w ith l a c t a t i o n .
The a u th o r s su g g est t h a t
t h i s i n c r e a s e c o u p le d w i t h i n c r e a s e s i n t h e w e i g h t s o f t h e l i v e r ,
h e a r t a n d mammory t i s s u e s
d u rin g l a c t a t i o n
e stim a te d
m a in te n an c e
10% i n c r e a s e
l a c t a t i n g cows.
in
may a c c o u n t f o r an
energy
re q u ire m e n ts
fo r
Tulloh (1966) r e p o r te d i n c r e a s e s i n t h e le n g th of th e
sm a ll i n t e s t i n e , th e i n t e r n a l c irc u m fe re n c e of th e lu m in a i n th e sm all
and l a r g e
in te stin e ,
and t h e w e i g h t s o f t h e m a in p a r t s o f t h e
a lim e n ta r y t r a c t o f l a c t a t i n g v e rs u s n o n - l a c t a t i n g tw in d a iry c a t t l e .
W a t e r - f i l l e d c a p a c i t i e s o f th e r e t i c u l o - rumen w ere 29% g r e a t e r f o r th e
l a c t a t i n g tw in s as w e ll.
He s u g g e s t s t h a t t h e s e c h a n g e s t a k e p l a c e
slo w ly and may be a s s o c i a t e d w ith m etabolism of abdominal f a t .
The o b s e r v a tio n s r e p o r te d g iv e e v id en ce to s u g g e s t th e n o tio n of
organ h y p e rtro p h y d u rin g l a c t a t i o n .
What i s n o t c l e a r i s t h e c asu a l
r e l a t i o n s h i p b e tw e e n i n t a k e and h y p e r t r o p h y .
o f f e r s t h r e e p o s s ib le cau ses o f h y p ertro p h y .
F e ll e t a l.
( 1 963)
The f i r s t i s th o u g h t to
be "work h y pertrophy" a s a r e s u l t of prolonged d i s t e n t i o n a s s o c i a t e d
w ith an i n c r e a s e i n food consumption.
Secondly, t h e r e may be hormonal
s t i m u l a t i o n o f t h e g u t w a l l b r o u g h t a b o u t by l a c t o g e n i c h o rm o n e s ,
la c ta tio n
its e lf
or
by s u c k l i n g .
H y p e rtro p h y
c o u ld a l s o
be a
f u n c t i o n a l a d a p t a t i o n n o t d i r e c t l y due t o in c r e a s e d i n t a k e , but to th e
12
i n c r e a s e d demands made on t h e body d u rin g l a c t a t i o n .
I t i s p o ssib le
t h a t food in ta k e i s c lo s e ly in v o lv e d i n th e e p i t h e l i a l h y p e r p la s ia
a s s o c i a t e d w ith l a c t a t i o n .
The most l i k e l y mechanisms ap p ea r to be
d i r e c t s t i m u l a t i o n of e p i t h e l i a l c e l l m etabolism d u rin g VFA a b s o r p tio n
a n d m eta b o lism ( F e l l and Weekes, 1975).
Level o f m ilk p ro d u c tio n a s i t a f f e c t s v o lu n ta ry i n t a k e has been
d i f f i c u l t to d e term in e f o r th e g ra z in g cow*
C o r r e la tio n c o e f f i c i e n t s
between m ilk y i e l d and d i g e s t i b l e o rg a n ic m a t t e r i n t a k e have been a s
h ig h a s .45 (C urran and Holmes,
1976).
Johnson e t a l .
1970) bu t a r e g e n e r a lly low er (Bines,
( 1966) f o u n d t h a t t h e tw o v a r i a b l e s w e re
in te r d e p e n d e n t, to th e e x te n t t h a t th e c o e f f i c i e n t o f c o r r e l a t i o n
between them approached 0.6.
i s t h e c a s u a l mechanism.
The r e l a t i o n s h i p i s confused a s t o which
I f th e energy re q u ire m e n ts f o r l a c t a t i o n a r e
met, th e n m ilk p ro d u c tio n would d e te rm in e th e amount of fo ra g e needed.
When i n t a k e i s r e s t r i c t e d by p h y s ic a l f a c t o r s however, m ilk y i e l d w i l l
more l i k e l y depend on th e amount o f m e ta b o liz a b le energy th e an im al
c a n d e r i v e fro m t h e f e e d ( B a i l e and F o r b e s ,
1 9 7 4 ).
Jones e t a l .
(1965) e s t i m a t e d summer d i g e s t i b l e o rg a n ic m a t t e r i n t a k e to be ab o u t
2 .3 % o f body w e i g h t f o r h ig h m i l k p r o d u c t i o n (38 l b s f a t - c o r r e c t e d
m ilk (FCM)Zd) and 2.1% f o r low m ilk producing (28 l b s FCM/d) A yrshire
c a ttle .
Mean l i v e body w e i g h t s d i d n o t d i f f e r b e tw e e n y i e l d l e v e l
groups.
F i e l d (1 966) f o u n d no r e l a t i o n s h i p b e tw e e n m i l k p r o d u c t i o n
a n d d ry m a t t e r i n t a k e a s m i l k y i e l d o f l a c t a t i n g d a i r y cows d ro p p e d
m arkedly from May to October.
These r e s u l t s may have been masked by
herbage a v a i l a b i l i t y and low l i v e w e ig h t changes.
b e e n shown t o
Milk p ro d u c tio n h a s
d ep en d on t h e am ount o f d i g e s t i b l e
e n e r g y a cow
13
consumes.
D ie ts c o n ta in in g 0 to 25% roughage c o n ta in s i m i l a r amounts
of d i g e s t i b l e energy.
As roughage i n c r e a s e s to 50 o r 75%, i n t a k e but
n o t m i l k y i e l d may become d e p r e s s e d .
At 100% r o u g h a g e , d i g e s t i b l e
energy i n t a k e becomes low enough to d e p re s s m ilk y i e l d of d a iry cows.
The cows examined produced between 12 and 20 kg/d m ilk and li v e w e i g h t
changes were g e n e r a lly n e g a tiv e f o r a l l r a t i o n s (Nelson e t a l . ,
1968
a s c i t e d by B ines, 1976).
P r e g n a n c y h a s b e en shown t o h a v e a p o s i t i v e e f f e c t on i n t a k e i n
t h e e a r l y s t a g e s b u t a n e g a t i v e e f f e c t l a t e r on.
C o m p re s s io n o f t h e
d i g e s t i v e t r a c t due t o f e t a l g ro w th i s a m a jo r i n f l u e n c e on i n t a k e
d u rin g pregnancy (B in es, 1971; Campling, 1966; Forbes,
1971).
As th e
volume of th e u te r u s p lu s abdominal f a t i n c r e a s e s , th e volume of rumen
c o n te n ts d e c r e a s e s a s does th e v o lu n ta r y in ta k e of roughage (Forbes,
1971).
This i s e s p e c i a l l y e v id e n t d u rin g th e l a s t f i v e weeks b e fo re
p a rtu ritio n .
In o rd e r to compensate f o r t h i s d e c li n e i n i n t a k e ,
th e
an im a l i s a p p a r e n tly a b le t o i n c r e a s e th e r a t e of passage of food a s
p re g n a n c y a d v a n c e s ( B i n e s ,
1971).
I n t a k e d e p r e s s i o n may a l s o be
r e l a t e d t o m e t a b o l i c c h a n g e s t h a t o c c u r w i t h p re g n a n c y (C a m p lin g ,
I 966).
O e s tr o g e n d e p r e s s e s f o o d i n t a k e a n d t h e r e i s a p r o g r e s s i v e
i n c r e a s e i n o e s tro g e n s e c r e t i o n d u rin g t h e second h a l f of pregnancy i n
ru m in an ts (F o rb e s, 1971).
I t i s g e n e r a l l y a c c e p t e d t h a t t h e cow d o e s n o t r e a c h m a t u r e
p h y s i c a l s i z e u n t i l s i x o r s e v e n y e a r s o f a g e ( B i n e s , 1976).
D u rin g
t h i s t i m e , u n d e r m o st c o n d i t i o n s , t h e e n e r g y c o s t o f a u n i t w e i g h t
g a in w i l l be between 1.2 and 8.0 m c al/k g of f a t - f r e e body w eight (NRC,
1984).
Assuming t h a t range fo r a g e s p ro v id e ap p ro x im a te ly 5 m cal/kg of
DM (Havstad,
and
1.6 k g
1984) a c o n tin u o u s ly grow ing cow would need between .25
of fo ra g e
ju st
to
sa tisfy
her
g r o w th
re q u ire m e n t.
V oluntary in ta k e i n c r e a s e s a s th e an im al a c h ie v e s m a tu re w e ig h t but
n o t i n d i r e c t p r o p o r tio n to th e i n c r e a s e s i n body w e ig h t.
For example
F o r b e s (1971) show ed t h a t c a t t l e w e i g h i n g 225 kg consum ed 5.6 kg o f
d ry m a t t e r w h e r e a s t h e same c a t t l e a t 425 kg consum ed 7 .2 kg, a n
in c re a se
o f 28% v e r s u s
a body w e i g h t i n c r e a s e
of
89%.
In ta k e
i n c r e a s e s when th e energy needs f o r grow th a r e h ig h e r, a b o u t I kg DM
f o r cows b e tw e e n t h e f i r s t and s e c o n d l a c t a t i o n o v e r t h e a d d i t i o n a l
i n t a k e due t o i n c r e a s e i n body w eig h t ( J o u r n e t and Remond, 1976).
In
m ature a n im a ls o f th e same b re e d in g , changes i n body w eig h t and v i s u a l
r a t i n g of body c o n d itio n h as been shown t o have l i t t l e r e l a t i o n s h i p to
i n t a k e d i f f e r e n c e s (J o h n s o n e t a l . , I 9 6 6 ).
A rn o ld (1970) a s c i t e d by
A l l i s o n (1 9 8 5 ) s t a t e d t h a t i n t a k e i s r e l a t e d t o body c o n d i t i o n , b u t
th e i n d i v i d u a l v a r i a t i o n of g ra z in g a n im a ls makes l i v e w e i g h t changes a
poor in d e x
of in ta k e
e v e n when a c c o u n t i n g
fo r
d iffe re n c e s
in
p ro d u c tiv ity .
Forage F a c to r s
G r a z in g r u m i n a n t s e x h i b i t d i s t i n c t s e l e c t i v i t y when p r e s e n t e d
w ith an a r r a y
of fo ra g e
c h o ice s
(M cC lym ont,
1 967).
R a n g e la n d s
ty p i c a l l y . p r o d u c e d iv e r s e v e g e ta tio n , n o t a l l of which i s p r e f e r r e d by
d o m e stic h e r b iv o r e s .
a f f e c ts in ta k e ,
I n o r d e r t o d e s c r i b e how g r a z i n g s t r a t e g y
i t i s n e c e ssa ry to i d e n t i f y th o se c h a r a c t e r i s t i c s o f
fo rag e th a t in flu e n c e p referen ce.
p a la ta b ility
per
se
a ffe c ts
T h e re i s no e v i d e n c e t h a t h i g h
to ta l
d a ily
fo o d
in ta k e ,
but
15
u n p a l a t a b i l i t y can c e r t a i n l y reduce i t (McClymont, 1967).
c an r e c o g n i z e p l a n t s by s e n s e s o f s i g h t ,
to u ch ,
The anim al
t a s t e and s m e l l ,
a lth o u g h t h e r e i s no r e l a t i o n s h i p between odor and p a l a t a b i l i t y (Van
Dyne e t a l . ,
q u a lity
1980).
of fo ra g e
P l a n t s e l e c t i o n d e p e n d s on t h e q u a n t i t y and
s p e c ie s,
u t i l i z a t i o n th e s p e c ie s .
and w i l l
change w ith
se a so n and
Among t h o s e f a c t o r s a s s o c i a t e d w i t h t h e
q u a l i t y of fo ra g e and hence i t s d i g e s t i b i l i t y , a r e t h e amount of f i b e r
and g re e n l e a f m a t e r i a l .
Grazing a n im a ls s e l e c t g reen i n p re fe re n c e
t o d ry m a t e r i a l (A rn o ld ,
1964).
The s e l e c t e d m a t e r i a l u s u a l l y i s
h i g h e r i n n i t r o g e n and lo w e r i n f i b e r ,
sig n ify in g th a t
chem ical
c o m p o s i t i o n may be a s s o c i a t e d w i t h
p h y sic a l
s e l e c t e d p l a n t p a r t s ( A r n o l d , 1964).
Many s t u d i e s ' h a v e d e p i c t e d a
re la tio n sh ip
b e tw e e n i n t a k e
c h a r a c te r is tic s of
and d i g e s t i b i l i t y .
d i g e s t i b i l i t y was in f lu e n c e d by f o r a g e n itr o g e n ,
In
one
stu d y ,
s o lu b le carb o h y d rate
c o n t e n t , a v a i l a b l e d ry m a t t e r and t i m e o f y e a r ( A r n o l d , 1 97 0 ).
Van
S o e s t (1965) c o n c lu d e d t h a t t h e i n t e r r e l a t i o n s h i p s among i n t a k e ,
d i g e s t i b l i t y and c h e m i c a l c o m p o s i t i o n a r e h ig h ly p l a n t o r ie n te d . He.
r e p o r te d a p o s i t i v e a s s o c i a t i o n betw een m a tu r ity and v o lu n ta r y i n t a k e
of t a l l fe s c u e ,
p o s s ib ly because of some u n p a la ta b le t o x i c s u b sta n c e
p r e s e n t i n t h e you n g p l a n t .
The o n ly c o n s i s t e n t e f f e c t f o r a l l
f o r a g e s w as fo u n d t o be t h e t o t a l f i b r o u s f r a c t i o n o r c e l l w a l l
c o n s t i t u e n t s whih i s i n v e r s e l y r e l a t e d t o d i g e s t i b i l i t y (Van S o e s t ,
I 98 2 ). As t h i s
f r a c t i o n in c re a s e s , v o lu n ta ry in ta k e d e c lin e s .
The
p o in t a t which t h i s f i b e r mass becomes l i m i t i n g o c c u rs when c e l l w a l l s
make up 50 t o 6 0% o f t h e f o r a g e d ry m a t t e r (Van S o e s t , I 9 65 ). On h ig h
q u a l i t y f o r a g e s t h e r e i s some e v id e n c e o f s a t i e t y b e f o r e rum en f i l l
16
fro m t h e f a c t t h a t i n t a k e o f c e l l w a l l s i s l o w e r . O sbourn (1974) a s
c ite d
by Van S o e s t ( 1982) s u g g e s t e d t h a t i n t a k e
of h ig h q u a lity
im m atu re f o r a g e s i s l i m i t e d because of th e high s o lu b le c a rb o h y d rate
c o n t e n t w h ic h may c a u s e a d ro p i n ru m en pH. T hin c e l l w a l l s o f
im m atu re f o r a g e s a r e n o t only more d i g e s t i b l e , but a r e more l i k e l y to
c o l l a p s e upon r u m i n a t i o n (Van S o e s t ,
1982). C o r b e t t e t a l . ( 1 963)
f o u n d DOM i n t a k e o f d a i r y cows t o f a l l by 20% a s d i g e s t i b i l i t y f e l l
fr o m 80 t o 6 8% d u r i n g t h e g ro w in g s e a s o n .
H o llo w a y e t a l . (1979)
show ed t h a t t h e i n t a k e o f l a c t a t i n g b e e f cows f e l l by 1.3 kg DM/d a s
f o r a g e DMD d ro p p e d fro m a b o u t 6 1% t o 5 8%.
Crude p r o t e i n c o n t e n t i s
h ig h ly r e l a t e d to th e p a l a t a b i l i t y of range f o r a g e s .
The c r i t i c a l
l e v e l o f p r o t e i n i s commonly i n t h e r a n g e o f 4 t o 6%.
V a lu e s below
t h i s l e v e l may l i m i t d i g e s t i o n ( S t r e e t e r e t a l . ,
ch em ical
c o n stitu e n ts
such a s l i g n i n
and
1 9 7 4 ).
ta n in s
are
S everal
g e n e ra lly
a s s o c i a t e d w i t h low p a l a t a b i l i t y , b u t h i g h ' p r o p o r t i o n s o f f a t s and
e t h e r e x t r a c t a r e c o r r e l a t e d w ith h ig h p a l a t a b i l i t y .
I t may be t h a t a
c o m b in a tio n
th e
of
c h em ical
compounds
ra th e r
th a n
in d iv id u a l
c o n s t i t u e n t s a f f e c t p a l a t a b i l i t y (Van Dyne e t a l . 1980).
Q u a lity of p la n t m a t e r i a l i s a l s o d eterm in ed by th e degree of use
o r a v a i l a b i l i t y of p r e f e r r e d v e g e ta tio n .
P i e p e r e t a l . (1959) a s
c i t e d by K a r t c h n e r a n d C am b ell (1979) s t a t e d t h a t i n t a k e d e c r e a s e s
w ith
heavy
g ra z in g as
d o e s th e
d ig e stib ility
of
th e
n u trie n ts
consumed. P r o te in , g ro s s energy, e t h e r e x t r a c t and phosphorous te n d t o
d e c re a se a s w e ll.
The g ra z in g bovine moves i n a h o r i z o n t a l plane but
s e l e c t s f o r a g e i n a v e r t i c a l p l a n e , c h o o s in g l e a f i n p r e f e r e n c e t o
s te m ( A r n o l d , 196 4).
A v a i l a b i l i t y in c lu d e s y i e l d a s w e ll a s th e
17
p h y sic a l
p re se n ta tio n
of
feed .
The p r e s e n c e
of
sp in e s,
p la n t
m o rp h o lo g y a n d e x c e s s i v e d ead g r o w th may i n h i b i t a c c e s s i b i l i t y t o
o th e rw is e p r e f e r r e d fo r a g e .
A study conducted by Arnold (19.64) showed
t h a t d i e t s b e tw e e n two g r o u p s o f s h e e p a t d i f f e r e n t s t o c k i n g r a t e s
w ere s i m i l a r i n q u a l i t y and c o m p o sitio n , y e t i n t a k e was s i g n i f i c a n t l y
l e s s f o r s h e e p a t t h e l o w e r s t o c k i n g r a t e due t o a n i m p e n e t r a b l e
p a s t u r e s t r u c t u r e and t h e i n a b i l i t y o f t h e s h e e p t o g r a z e p r o p e r l y .
In ta k e d e p re s s io n due to d e crea se d f o r a g e a v a i l a b i l i t y h a s been shown
by o t h e r r e s e a r c h e r s a s w e l l ( A l den a n d W h i t t a k e r ,
1970). There i s l i t t l e
herbage.
th a t
1970; A rn o ld ,
c o n s is te n c y a s t o th e lo w e r l i m i t of adeq u ate
Hodgson and W ilkinson (1967) a s c i t e d by Arnold (1970) found
in ta k e
a v a ila b ility
of
cow s,
h e ife rs
and
c a lv e s
was
u n affected
was r e d u c e d fro m 8,000 t o 2 ,0 0 0 k g / h e c t a r e .
when
N a stis
(1979) found t h a t only 143 kg DM/hectare was n e c e ssa ry f o r th e optimum
in ta k e of h e i f e r s ,
H a v s ta d e t a l .
a v a ila b ility
w h i l e H andl and R i t t e n h o u s e (1972) a s c i t e d by
( 1983) d e s c r i b e d a d e c l i n e i n i n t a k e when f o r a g e
was l e s s th a n 176 k g / h e c t a r e .
Havstad (1981) e s tim a te d
th e i n t a k e of h e i f e r s to be 1. 3% BW th ro u g h o u t a fo r a g e supply of 880
kg DM/hectare t o 284 kg DM/hectare.
Under bulk l i m i t i n g c o n d itio n s ,
w h e re d i g e s t ! b l i t y e n e r g y c o n t e n t i s l e s s t h a n 2.7 k c a l / g DM, t h e
q u a n t i t y of fo ra g e a v a i l a b l e to h e i f e r s may n o t a f f e c t v o lu n ta r y d a ily
i n t a k e ( H a v s ta d e t a l . , 1983).
O th e r f a c t o r s su c h a s d e c l i n e i n t h e
q u a l i t y of a v a i l a b l e fo r a g e or g ra z in g f a t i g u e may be r e s p o n s ib le f o r
r e d u c t i o n i n th e v o lu n ta r y in t a k e of th e s e an im als.
A v a i l a b i l i t y may be more c l o s e l y r e l a t e d to p la n t h e i g h t r a t h e r
th a n y i e l d
w h ic h may a c c o u n t f o r
th e la c k
of ag re em e n t i n
th e
18
lite ra tu re
b e tw e e n i n t a k e and h e r b a g e a v a i l a b i l i t y .
I n a s tu d y
conducted w ith lam bs and y e a r l i n g sheep, i n t a k e in c r e a s e d r a p i d l y w ith
i n c r e a s i n g t i l l e r l e n g t h up t o 15 cm.
T h e r e a f t e r , t h e r e w as l i t t l e
c h a n g e i n i n t a k e a s t i l l e r l e n g t h i n c r e a s e d ( A lld e n a n d W h i t t a k e r ,
1970).
A s.fo r a g e becomes s c a rc e , in c r e a s e d g ra z in g tim e i s needed t o
m a in ta in th e same i n t a k e l e v e l on p a s t u r e s o f low fo r a g e a v a i l a b i l i t y .
In ta k e per hour d e c re a s e s a s g ra z in g tim e i n c r e a s e s , because lo w er
i n t a k e p e r b i t e i s n o t f u l l y compensated by i n c r e a s i n g b i t e p e r m inute
(A rnold, 1964).
Environm ental F a c to rs
B e s i d e s t h e m ore a p p a r e n t c o m p o n e n ts c r e a t i n g t h e f o o d i n t a k e
model i n g ra z in g ru m in a n ts ,
th e r e a r e o th e r s t i m u l i su rro u n d in g the
anim al which i n h i b i t or enhance i t s f o r a g in g mode.
S o c ia l i n t e r a c t i o n
and e n v iro n m e n ta l te m p e r a t u r e a r e e s p e c i a l l y i m p o r t a n t f o r a n i m a l s
exposed to a v a r i e t y of l i v i n g c o n d itio n s .
b e h av io r e x h i b i t e d by young a n im a ls,
B esid e s t h e i n s t i n c t i v e
McClymont (1967) d i s c u s s e s f o u r
l e a r n i n g p r o c e s s e s t h a t d e term in e s e l e c t i v i t y and c o n se q u e n tly forage
in ta k e .
The f i r s t i s a l l e l o m i m e t i c o r m im icing b e h a v io r most o f te n
d i s p l a y e d a s i m i t a t i o n o f t h e dam.
Sheep d i e t s o f dams and t h e i r
d a u g h te rs d i f f e r e d l e s s th an u n r e l a t e d s h e e p a s d a m / d a u g h t e r g ro u p s
t e n d t o o c cu p y t h e same home r a n g e and h e n c e g r a z e t h e same p l a n t
c o m m u n ities.
co m p rise
I t t h e r e f o r e a p p e a r s t h a t t h e n u m e ro u s g r o u p s t h a t
a flo c k
of
sheep
do n o t
environm ent (H unter and M iln e r, 1963).
o c cu p y t h e
same n u t r i t i o n a l
Secondly, h a b i t or p re fe re n c e
due t o p re v io u s e x p e rie n c e h a s an e f f e c t on s e l e c t i v i t y when a n im a ls
19
a re p re se n te d w ith a d iv e rs e fo rag e re s o u rc e .
A rn o ld a n d M a i l e r
( I 977) a s c i t e d by A rn o ld a n d D u d z in s k i (197 8) s t a t e d t h a t i n t a k e of
s h e e p i n e x p e r i e n c e d on p a s t u r e may be l o w e r by 50% t h a n t h a t o f
e x p erien c e d
a v o id a n c e
in to x ic a tio n .
sheep.
of
A th ird
p la n ts
le arn ed resp o n se
p ro d u c in g
a
n e g a tiv e
to
g ra z in g
resp o n se
is
an
such
as
The chances of an an im al l e a r n i n g from such an e f f e c t
a r e reduced when t h e c u m u la tiv e damage i s slow a c t i n g and when a la r g e
s e l e c t i o n of p la n ts i s a v a i l a b l e .
L a s t l y , h a b i t u a t i o n can c a u s e an
an im a l to reduce s e l e c t i v i t y when r e p e a te d o r co n tin u ed ex p o su re to a
p a rtic u la r
food
p ro m o tes
a d d ic tio n
( A rn o ld
and
M a ile r,
1977).
H a b i t u a t i o n c an be a c c e l e r a t e d by a n u t r i e n t d e f i c i e n c y o r fro m a
p o sitiv e p a la ta b ility re a ctio n .
The f a c t t h a t g ra z in g r u m in a n ts l e a r n
from p re v io u s e x p e rie n c e s le n d s evidence t o a hedaphagic r a t h e r than
a euphagic f o r a g i n g s t r a t e g y .
G razing ru m in a n ts i n t e r a c t s o c i a l l y w ith o th e r s , m u tu a lly causing
c h a n g e s i n g r a z i n g t i m e and d i s t r i b u t i o n .
I t i s c o n ce iv a b le th a t
p y sc h ic
ra te s
stre ss
in d u c ed
by h ig h
sto c k in g
w ith
low
fo rag e
a v a i l a b i l i t y may r e d u c e i n t a k e o f a n i m a l s low i n t h e s o c i a l o r d e r
(McClymont, 1967).
Sheep have shown a g r a z in g h ie r a r c h y i n which th e
weaker ewes a r e f o r c e d to d is p e r s e to th e p o o rer p a tc h e s of v e g e t a t i o n
(Hunter and M iln e r,
1963).
S o c ia l i n t e r a c t i o n p la y s an im p o r ta n t but
v a r i a b l e r o l e i n a f f e c t i n g g ra z in g tim e .
T ribe (1950) r e p o r t e d t h a t
supplem ented sheep grazed lo n g e r when mixed w ith unsupplem ented sheep,
an e f f e c t re g a rd e d a s s o c i a l f a c i l i t a t i o n .
Holder (1962) a ls o no ted a
s o c i a l i n h i b i t i o n e f f e c t on mixed unsupplem ented sheep,
t o reduce g r a z in g tim e.
cau sin g them
20
T h e r m o s t a t i c c o n t r o l o f f e e d i n t a k e w as r e v i e w e d by B a i l e and
F o r b e s (1 9 7 4 ) , a n d J o n es (1 9 7 2 ).
I n o r d e r t o m a i n t a i n body h e a t ,
a n i m a l s m u st e a t , b u t t o p r e v e n t h y p e r t h e r m i a , e a t i n g m u st c e a s e
( B ro b e c k , 1948 a s c i t e d by B a lc h a n d C a m p lin g , I 962),
J o n e s (1972)
s t a t e d t h a t t h e r m o s t a t i c r e g u l a t i o n of fe e d in t a k e i n ru m in a n ts i s a
re s p o n se t o en v iro n m e n ta l te m p e ra tu re r a t h e r th an h e a t g e n e ra te d from
m e ta b o lism
of
feed \ n u t r i e n t s .
T h e re i s
g e n e ra lly
a p o sitiv e
r e l a t i o n s h i p b e tw e e n t e m p e r a t u r e a n d i n t a k e , b u t a t e x t r e m e l y h i g h
t e m p e r a t u r e s , i n t a k e i s h a l t e d (Van Dyne e t a l . , I 9 8 0 ).
C o n tin u o u s
h ig h te m p e ra tu re s d e p re ss i n t a k e such t h a t z e r o energy balan ce cannot
be m a in ta in e d , and above 40° C ru m in a n ts o f te m p e ra te c l i m a t e s do n o t
e a t a t a l l ( B a i l e and F o r b e s , 1974).
I n c r e a s i n g t h e t e m p e r a t u r e of
ru m en c o n t e n t s fro m 3 8° C t o 4 1 .3 ° C d e c r e a s e d i n t a k e by I 5% ( B a i l e
and F o r b e s , 1974).
In o rd e r to m a in ta in in ta k e d u rin g h o t w e ath e r,
f r e e - r a n g i n g a n i m a l s w i l l a d j u s t t h e i r g r a z i n g t i m e by g r a z i n g a t
n i g h t o r d u r i n g t h e c o o l e s t p a r t o f t h e day (A rn o ld a n d D u d z in s k i,
1978; McClymont, 1967) .
I n c r e a s e s i n f o o d i n t a k e due t o c o l d s t r e s s a r e n e c e s s a r y t o
m a i n t a i n e n e r g y b a l a n c e and body t e m p e r a t u r e .
l o s s , th e g r e a te r th e in c r e a s e i n in ta k e .
The g r e a t e r t h e h e a t
The f o o d i n t a k e r a t e o f
d a i r y cow s i n c r e a s e d by a b o u t 3 k g a s t h e d a i l y a i r t e m p e r a t u r e
d e c r e a s e d fro m 4 t o I ° C and c o n t i n u e d f o r a t l e a s t 24 h o u r s a f t e r
c o l d s t r e s s (McDonald and B e l l ,
1980).
1958 a s c i t e d by Van Dyne e t a l . ,
T ypical low c r i t i c a l te m p e ra tu re s ,
below which th e anim al i s
unab le t o m a in ta in body h e a t, a r e b e lie v e d to be betw een -10 and -20 C
fo r
dry,
p regnant
beef
cow s.
Recent s t u d i e s have a ls o
shown a
21
d e p re s s io n i n th e a b i l i t y of ru m in a n ts to d ig e s t fe e d d u rin g c o ld
stre ss,
in d e p en d e n t of t h e i r food i n t a k e .
D i g e s t i b i l i t y d e c re a se s by
about 2 p e rc e n ta g e u n i t s p e r 10 C drop i n am bient te m p e ra tu re (Young
1980). A f t e r s h e a r i n g , DOM i n t a k e s r o s e by 42-62% i n g r a z i n g s h e e p .
The i n c r e a s e was e x p la in e d by an a c c e l e r a t e d r a t e of energy metabolism
induced by c o ld s t r e s s (4 -2 7 ° C) (Wheeler e t a l . , 1963) .
The e f f e c t o f day l e n g t h on i n t a k e i s n o t c l e a r l y u n d e r s t o o d .
1
One s tu d y w i t h s h e e p show ed t h a t a n i m a l s w i t h 16 h o u r s o f l i g h t p e r
day had 6% h i g h e r f o o d i n t a k e s t h a n t h o s e w i t h 8 h o u r s o f l i g h t
( E l-S h ah at e t a l . , 1974 as c i t e d by Van Dyne e t a l . , 1980) .
P ro d u c tiv e E f f ic ie n c y o f Free-R anging Cows Varying i n B io lo g ic a l
P o te n tia l
In f o rm a tio n on t h e fe e d e f f i c i e n c y of g ra z in g cows i s e s s e n t i a l l y
n o n e x iste n t.
C o n sid e rin g
th e
d iffic u lty
in
o b ta in in g
d e te r m in a tio n s o f fo ra g e in t a k e f o r ra n g e la n d c a t t l e ,
re lia b le
e f f o r t s t o make
c o n c l u s i v e i n t e r p r e t a t i o n s o f t h e b a l a n c e b e tw e e n f e e d i n p u t a n d
p ro d u c tiv e o u tp u t a r e i n t h e p r i m i t i v e s ta g e s .
Although some of th e
p r i n c i p l e s in v o lv e d i n e f f i c i e n c y d e te r m in a tio n s of s t a l l - f e d a n im a ls
may a p p l y t o
th e g ra z in g an im a l,
many more f a c t o r s a f f e c t
th e
e f f i c i e n c y o f f e e d u t i l i z a t i o n on t h e r a n g e due t o t h e m ore v a r i e d
environm ent.
Confounding t h e s i t u a t i o n f u r t h e r i s t h e energy balance
of th e a n im a l,
d e t e r m i n e d by i t s g r a z i n g a c t i v i t i e s a n d need f o r
th e rm a l r e g u la tio n .
A f t e r e s t i m a t i n g t h e f o r a g e i n t a k e and f o r a g e
d i g e s t i b i l i t y f o r f r e e - r a n g i n g ru m in a n ts ,
th e re m a in in g v a r i a t i o n i n
an im al perform ance w i l l be i n c o r p o r a te d i n i t s e f f i c i e n c y (Van S o e s t,
1982 ) .
22
In r e l a t i n g phenotype t o th e e f f i c i e n c y of g ra z in g cows, Holloway
and B u tts
(1983) n o t e d
th a t
e ffic ie n c y
of
m ilk
p r o d u c t i o n w as
p o s i t i v e l y r e l a t e d t o l e v e l of m ilk p ro d u c tio n and n e g a t i v e l y r e l a t e d
to s t r u c t u r a l s i z e r e g a r d l e s s of p a s t u r e q u a l i t y .
S tru c tu ra lly la rg e r
cows g ra z in g fe sc u e -le g u m e p a s t u r e s consumed more fo ra g e but produced
no m ore m i l k t h a n s m a l l e r cow s.
e ffic ie n tly .
T h e r e f o r e , t h e y p ro d u c e d m i l k l e s s
In a d d i t i o n , l a r g e r cows g ra z in g fe s c u e d id n o t i n c r e a s e
i n t a k e i n p r o p o r t i o n t o t h e i r s i z e a n d w e re a g a i n l e s s e f f i c i e n t
p ro d u c e rs o f m ilk and c a l f g a in th a n cows o f s m a l le r s t r u c t u r a l s iz e .
The r e l a t i o n s h i p between s t r u c t u r a l dim en sio n and e f f i c i e n c y f o r cows
g r a z i n g f e s c u e w as c o n fo u n d e d by c h a n g e s i n cow w e i g h t and f a t n e s s
d u rin g l a c t a t i o n and c a l f weaning w e ig h t:
cow w e ig h t r a t i o s .
F a tn e ss
w a s n o t s i g n i f i c a n t l y r e l a t e d t o m i l k p r o d u c t i o n f o r cows g r a z i n g
e i t h e r f e s c u e - le g u m e o r f e s c u e p a s t u r e s ,
b u t t h i n cows g r a z i n g
fe s c u e ten d ed t o be more e f f i c i e n t p ro d u c e rs of m ilk th a n f a t cows.
R e s u lts from N utt e t a l . (1980) show t h a t s t r u c t u r a l l y l a r g e cows
h a v e l a r g e r ru m en c a p a c i t i e s thaiq s m a l l cow s.
A lth o u g h cows w i t h
l a r g e rumen c a p a c i t i e s consumed more fo r a g e on low q u a l i t y p a s tu r e s
(DM d i g e s t i b i l i t y
o f 55%) t h a n cow s w i t h s m a l l e r ru m e n s ,
rum en
c a p a c i t y w as n o t r e l a t e d t o e i t h e r m i l k p r o d u c t i o n o r c a l f w e a n in g
w e ig h t.
These r e s u l t s su g g est t h a t cows w ith l a r g e rumen c a p a c i t i e s
u tiliz e
t h e i r e x t r a n u t r i e n t s f o r f u n c t i o n s o th e r th a n m ilk
p ro d u c tio n .
In
an
effo rt
to
d e term in e
th e
in flu e n c e
of
season
on t h e
e f f i c i e n c y o f cows v a r y i n g i n f r a m e s i z e a n d f a t n e s s , H o llo w a y and
B u tts (1984) concluded t h a t much more v a r i a t i o n i n m ilk p ro d u c tio n and
23
c a l f g r o w th w as n o t e d f o r cows g r a z i n g f e s c u e le g u m e d u r i n g t h e
s p rin g .
E f f ic ie n c y of co n v ersio n of DE above m aintenance t o m ilk was
a g a in n e g a ti v e ly r e l a t e d t o fram e s i z e f o r cows g ra z in g both fe scu e le g u m e a n d f e s c u e p a s t u r e s , b u t w as much more p ro n o u n c e d f o r cows
g ra z in g f e s c u e .
A c c o rd in g t o K ro n b e rg (1983) l a c t a t i n g H e r e f o r d cows g r a z i n g
sum m er f o o t h i l l r a n g e consum ed .84 kg OM p e r kg o f m i l k p ro d u c e d
d u r i n g J u n e , I 983 > w h i l e 3 / 4 S im m e n ta l x 1 /4 H e r e f o r d cows r e q u i r e d
1.12 kg p e r kg m i l k .
The H e r e f o r d s w e ig h e d a n a v e r a g e o f 441 kg and
y i e l d e d a p p r o x i m a t e l y 11 k g o f m i l k d a i l y w h i l e t h e 3 / 4 S im m e n ta ls
w e ig h e d 563 kg and p ro d u c e d a b o u t 1 2 kg p e r day.
The r e l a t i o n s h i p
b e tw e e n e f f i c i e n c y o f m i l k y i e l d a n d body s i z e o f d a i r y cowswas
th o ro u g h ly
re v ie w ed
by M o r r i s and W i l t o n
(1 9 7 6 ).
The a v e r a g e
c o r r e l a t i o n b e tw e e n d a i r y e f f i c i e n c y ( m i l k y i e l d / f e e d i n t a k e ) and
m easures of body s i z e was found to be -0.18 and g e n e tic , c o r r e l a t i o n s
a v erag e d -0 .3 7 .
In c o n tr a s t,
o v e r a l l c o r r e l a t i o n s b e tw e e n d a i r y
e f f i c i e n c y and l e v e l o f m ilk y i e l d w ere 0.81 and g e n e ti c c o r r e l a t i o n s
w ere about O.89.
The o v e r a l l r e l a t i o n s h i p between m ilk y i e l d and body
s i z e was 0.33 w i t h i n b re e d s of d a iry c a t t l e w h ile g e n e ti c c o r r e l a t i o n s
a v e r a g e d 0 .1 4 .
Holmes (1973)
fo u n d no n u t r i t i o n a l
a d v a n ta g e i n
in c r e a s e d body s i z e f o r m ilk p ro d u c tio n , bu t an a p p a re n t advantage f o r
m eat p r o d u c tio n .
R e s u l t s fro m Bowden ( 198I ) s u p p o r t a g e n e r a l
c o n c lu s io n t h a t th e c o n v ersio n of energy consumed by a cow and c a l f t o
w e i g h t o f w eaned c a l f d u r i n g t h e f i r s t l a c t a t i o n d o e s n o t d i f f e r
sig n ific a n tly
b e tw e e n
b io lo g ic a l
ty p e s
of
cows u n d e r
th e
same
24
management.
Other m easures o f e f f i c i e n c y a r e o u ts id e t h e c o n tex t of
t h i s l i t e r a t u r e review a lth o u g h e q u a lly im p o r ta n t.
P rev io u s In ta k e E stim a te s Using Chromic Oxide
When the d i e t s e l e c t e d by d i f f e r e n t groups of g r a z in g a n im a ls i s
assumed t o be of th e same d i g e s t i b i l i t y ,
e r r o r s i n comparing r e l a t i v e
i n t a k e s a r e c r e a t e d fro m i n a c c u r a c i e s i n e s t i m a t i n g f e c a l o u t p u t
( L a n g l a n d s , I 97 5 ).
A lth o u g h t h e r e a r e many m e th o d s o f d e t e r m i n i n g
f e c a l o u tp u t i n range n u t r i t i o n ,
(CR2 Og)
as
an e x t e r n a l
in d ic a to r
t h e u s e o f chrom ium s e s q u i o x i d e
is
co n sid e re d to
be t h e m ost
s a t i s f a c t o r y (L a n g e la n d s, 1975).
The u se o f CRgOg h a s c e r t a i n l i m i t a t i o n s , b u t t h e s e h a v e b e e n
t h o r o u g h l y i d e n t i f i e d by v a r i o u s r e s e a r c h e r s ( R a l e i g h e t a l . , 1980;
Kotb a n d L u c k e y , I 972; L a n g la n d s , 1 9 7 5 ).
Once t h e s e p a r a m e t e r s a r e
d e f i n e d and t h e t e c h n i q u e i s a d m i n i s t r a t e d a c c o r d i n g l y , r e l i a b l e
e s t i m a t e s o f f e c a l o u t p u t and s u b s e q u e n t l y f o r a g e i n t a k e can be
o b ta in e d .
Appendix t a b l e 7 i s an assem blage of i n t a k e e s t i m a t e s and
t h e i r c o r r e s p o n d i n g d i g e s t i b i l i t y v a l u e s f o r v a r io u s b reed s of cows
u s in g th e chrom ic ox id e te c h n iq u e .
25
■ MATERIALS AND METHODS
The study s i t e was l o c a t e d about 50 km south o f Havre, Montana i n
th e Bear Paw Mountains.
to
i\0%.
The p a s tu r e was 81 ha i n s i z e w ith s lo p es up
E le v a tio n averaged
fro m 45.7 t o 50.8 cm.
( F e s tu c a s c a b r e l l a ) .
1300 m w ith annual p r e c i p i t a t i o n ran g in g
U pland a r e a s w e r e d o m in a te d by ro u g h f e s c u e
Idaho fe s c u e ( F e s tu c a id a h o e n s is ),
and bluebunch
w h e a t g r a s s ( A g ro p y ro n s p i c a t u m ) w i t h an open p o n d e r o s a p in e ( P in u s
ponderosa) o v e rs to ry .
K en tu ck y b l u e g r a s s ( Poa p r a t e n s i s ) d o m in a te d
th e lo w lan d v e g e t a t i o n .The a r e a i s c l a s s i f i e d i n t h e F o r e s t-G ra s s la n d
c o m p le x o f t h e w e s t e r n g l a c i a t e d p l a i n s , and i s t y p i c a l o f f o o t h i l l
ra n g e la n d i n n o rth c e n t r a l Montana ( USDA-SCS 1976).
The cows used i n th e study w ere randomly s e l e c t e d a s 6 o r 7 y e a r
o l d s fro m t h e H avre R e s e a r c h S t a t i o n h e r d .
A ll cows w e r e ra n d o m ly
a r t i f i c i a l l y in s e m in a te d t o e i t h e r C h a r l o i s o r T a r e n t a i s e b u l l s . I n
1983, 6 dry and 6 l a c t a t i n g cows from s t r a i g h t b r e d H erefo rd (HH) and
75%
S im m en tal-5 0 % H e r e f o r d (3S 1H) b r e e d s w e re u s e d .
a d d i t i o n a l b reed s groups w ere examined,
I n 1984,
3
in c lu d in g 25% Sim m ental-75%
H e r e f o r d ( I S3 H), 50% S im m en tal-5 0 % H e r e f o r d (SH), and 50% Angus-50%
H erefo rd (AH). S ix l a c t a t i n g
cows i n each breed w ere used f o r a t o t a l
o f 30 head. To e s t i m a t e d a ily f o r a g e . o r g a n i c m a t t e r i n t a k e (OMI) th e
f o ll o w i n g e q u a tio n was used: OMI = d a i l y f e c a l o utput (OMB) / ( I -IVOMD
o f t h e d i e t ) . F e c a l o u t p u t f o r e a c h cow w as e s t i m a t e d d u r i n g J u n e ,
J u l y and A ugust each y e a r u s i n g t h e c h r o m ic o x id e (C r2 Og) d i l u t i o n
te c h n iq u e .
T o ta l f e c a l c o l l e c t i o n s from dry cows equipped w ith f e c a l
bags w ere a ls o conducted d u rin g t h e 1983 t r i a l to d e r iv e a c o r r e c t i o n
f a c t o r f o r th e d i f f e r e n c e s between a c t u a l f e c a l o u tp u t and p r e d ic te d
26
f e c a l outp u t u sin g C^Og. F ecal c o l l e c t i o n bags and f e c e s - u r i n e f l a p s
a s d e s c r i b e d by K a r t c h n e r and R i t t e n h o u s e (1979) w e re p l a c e d on t h e
cows f o r 4 c o n se c u tiv e days each month and bags w ere changed every 12
h o u rs.
C o lle c te d f e c a l m a te r ia l
w as w ie g h ed
th e n
s u b sa m p le d .
Subsamples w ere f r o z e n f o r dry m a tte r and o rg a n ic m a tte r a n a l y s i s a t a
la te r
d a te.
B e g i n n in g
5 days
p rio r
to
fecal
c o n tin u in g th ro u g h o u t th e c o l l e c t i o n p e rio d ,
c o lle c tio n s,
and
cows w e re d o sed a t
a p p ro x im a te ly 1800 h w ith a 10 g Cr2O^ powder b olus. At th e same tim e ,
r e c t a l grab sam p les w ere ta k e n from each cow and fr o z e n . To determ in e
chrom ium c o n t e n t , g r a b s a m p l e s w e re th a w e d , d r i e d a t 40 C, g ro u n d
th ro u g h
a 2 mm s c r e e n ,
and p r e p a r e d
fo r
a to m ic
a b so rp tio n
s p e c t r o p h o t o m e t r y a c c o r d i n g t o W i l l i a m s e t a l . ( 1 962). A ll f e c a l
sam p les w ere an aly se d f o r dry m a tte r and o rg a n ic m a t t e r f o llo w in g AOAC
( I 970) p r o c e d u r e s . D a ily f e c a l d ry m a t t e r (DM) o u t p u t w as e s t i m a t e d
u s i n g t h e e q u a t i o n : f e c a l DM o u p u t / d = (10 g Cr2 Og f e d /d /
%
Cr2 Og i n
dry f e c a l sample) x 100.
Forage sam ples f o r d e te r m in a tio n o f i n v i t r o d i g e s t i b i l i t y were
o b ta in e d
over
f i s t u l a t e d cows.
a 3 -d a y
p e rio d
each
m onth
u sin g
E x tru sa was im m e d ia te ly fro z e n ,
d rie d p rio r to la b o ra to ry a n a ly s is .
6
e so p h o g e a lly
th e n l a t e r f r e e z e -
O r g a n ic m a t t e r d i g e s t i b i l i t y
(OMD) was d eterm in ed u s in g th e Barnes m o d if ic a tio n o f th e T i l l e y and
T erry i n v i t r o te ch n iq u e ( H a r r is , 1970). Rumen f l u i d was o b ta in e d from
a
rume n -c a n n u la t ed cow on an ad l i b i t u m g r a s s hay d i e t t h a t was 55%
d i g e s t i b l e (IVOMD). This hay was used a s th e s ta n d a rd i n th e i n v i t r o
t r i a l s t o c o r r e c t IVOMD v a lu e s f o r e x tr u s a samples.
27
To e x p r e s s i n t a k e a s a p e r c e n t o f body w e i g h t , a l l cows w e re
w e ig h e d a f t e r a 12- h r s h r i n k p e r i o d p r i o r t o f e c a l c o l l e c t i o n s e ac h
month.
Hip h e i g h t s w ere measured d u rin g t h e f i n a l w eighing t o d e riv e
h e i g h t : w eight r a t i o s ( h t: w t ) a s an i n d i c a t i o n of body c o n d itio n .
Milk p ro d u c tio n f o r a l l cows used i n 1984 was e s t i m a t e d u s in g t h e
w e ig h -s u c k le -w e igh te c h n iq u e fo llo w in g f e c a l c o l l e c t i o n s each month.
The d a t a w e re a n a l y s e d a s a s p l i t - p l o t d e s i g n . L e a s t s q u a r e s
a n a l y s i s of v a r ia n c e was conducted u s in g S t a t i s t i c a l A n a ly sis System’s
(SAS) General L in e a r Model pro ced u re t o d eterm in e breed d i f f e r e n c e s i n
in ta k e ,
m ilk p ro d u c tio n ,
body w e i g h t ,
and w t:h t. r a t i o .
The
i n d e p e n d e n t v a r i a b l e s i n c l u d e d i n e a c h m odel o f t h e a b o v e f a c t o r s
w e r e : b r e e d , m o n th , a b r e e d X m onth i n t e r a c t i o n , s e x o f c a l f , s i r e
breed of c a l f ,
and c a l f ag e.
L e a s t s q u a r e s mean s e p a r a t i o n was
perform ed u s in g th e L e a s t S i g n i f i c a n t D iffe re n c e (LSD) p ro ced u re.
28
RESULTS
I n ta k e D iff e re n c e s Among Breeds - IQ8^ T r i a l
Monthly l e a s t sq u a re s mean i n t a k e s ,
body w ieg h t p er day
(%
ex p ressed a s a p e rcen tag e of
BW/d) f o r l a c t a t i n g 3S1H and HH cows a re g iv en
i n t a b l e I . No s i g n i f i c a n t d i f f e r e n c e s w ere found between t h e breeds
when a v e r a g e d o v e r t h e sum m er, o r w i t h i n a m onth. M o n th ly v a l u e s
d e crea se d th ro u g h o u t th e study p e rio d ,
i n August compared to June and J u ly .
but dropped s i g n i f i c a n t l y only
Body w e ig h t was n o t s i g n i f i c a n t
i n e x p la in in g th e v a r i a t i o n i n in t a k e when added a s a c o v a r ia te ,
and
no s t a t i s t i c a l d i f f e r e n c e s i n body w e ig h t were d e te c te d between th e
b r e e d s (P>.10) ( T a b le 4 ).
M ilk p r o d u c t i o n d a t a w e re u n a v a i l a b l e f o r
1983. In ta k e and body w e ig h t a n a l y s i s of v a r ia n c e t a b l e s a r e g iven i n
Appendix t a b l e s 8 and 9 .
1984 T r i a l
B re ed (P < .0 1) a n d month (P<.06) i n f l u e n c e d i n t a k e o f t h e f i v e
b re e d s i n 1984 (Appendix t a b l e 10).
I n ta k e v a lu e s between b reed s and
months a r e shown i n t a b l e 2. When averag ed a c r o s s months, i n ta k e s f o r
1S3H, BH, AH, SH, and 3 SI H w e re 2 .2 , 2 .3 , 2 .5 , 2 .6 , and 2.8% BW/d
r e s p e c t i v e l y . When a v e r a g e d a c r o s s b r e e d s , i n t a k e i n J u n e d e c l i n e d
fro m 2.9% BW/d t o 2.2% BW/d i n A u g u st. When m i l k p r o d u c t i o n , body
w e ig h t, and w t:h t r a t i o s were added a s c o v a r ia te s i n t h e in ta k e model,
m ilk p ro d u c tio n acco u n ted f o r a p p ro x im a te ly 60% of th e v a r i a t i o n i n
i n t a k e b e tw e e n b r e e d s (P < .0 1 ). T h is w a s d e t e r m i n e d by d e s i g n i n g a
l i n e a r c o n t r a s t u sin g breed d e v ia t io n s from th e o v e r a l l l e a s t sq u ares
29
Table I . 1983 D aily fo ra g e in t a k e (% BW 0MB) f o r l a c t a t i n g cows.
Breed
Junel
J u lv
August
Mean
HH
3.1 + . 2a
3 .0
±
.Ia
2 .2 ±. . 2a
2.8 + . I a
3S1H
2 . 8 + . 2a
3.1
±
.Ia
2.3 + . 2a
2.7 + - I a
Mean1
2
3 .0 + . 2a
3 .0 + . I a
2.3 + . 2b
^Means w i t h i n a colum n f o l l o w e d by a common s u p e r s c r i p t a r e
s i m i l a r (P<.07) .
2 Means w i t h i n t h e row f o l l o w e d by a common s u p e r s c r i p t a r e
s i m i l a r (P < .0 7 ).
Table 2 . 1984 D aily fo rag e in ta k e (% BW 0MB) f o r f iv e 1 cow breeds
Breed
Junel
J u lv
I S3 H
2.6 + . 2a
2.2 + . I a
I .9 + . 2a
2 .2
HH
2.7 + . 2ab
2 .2 + . I ab
2.1 + . 2ab
2 .3 ±. . I ab
AH
3.0 + . 2bc
2.4 ± . I ab
2.2 + . 2bc
2.5 + . I bc
SH
3.0 + . 2bc
2 .5 ± . I bc
2 .2 + . 2bc
2.6 + . I cd
3S1H
3 .2 + . 2C
2.8 + . I c
2.4 + . 2°
2.8 ±. . I d
Mean2
2 .9 + . 2a
2 .4 + . I b
2 .2 + . 2b
August
Mean
±
.Ia
1 Means w i t h i n a column fo llo w e d by a common s u p e r s c r i p t a r e s i m i l a r
( P < .0 7 ) .
2 Means w ith in th e row fo llo w e d by a common s u p e r s c r i p t a r e s i m i l a r
(P<.0 5 ) .
30
mean f o r m i l k p r o d u c t i o n .
The sums o f s q u a r e s g e n e r a t e d by t h i s
c o n t r a s t a c c o u n t e d f o r a b o u t 6 0 % o f t h e i n t a k e sum s o f s q u a r e s f o r
bree^d.
Body w i e g h t w as s i g n i f i c a n t
(P<.05) i n e x p l a i n i n g i n t a k e
d i f f e r e n c e s among b reed s a s w e ll.
W ith in -b re e d v a r i a t i o n i n in t a k e was p a r t i a l l y e x p la in e d by body
w e ig h t
(P<. 0 1) and w tz h t r a t i o
(P<.0 5 ),
b u t m i l k p r o d u c t i o n was
n o n sig n ific a n t.
Milk P ro d u ctio n
Mean m o n th ly m i l k p r o d u c t i o n f o r a l l b r e e d s u s e d i n 1984 a r e
shown i n t a b l e 3»
The SH and 3 S I H b r e e d s p ro d u c e d 5.5 k g /d a y m ore
m i l k d u r i n g t h e summer t h a n t h e I S3H, HH and AH b r e e d s .
M onthly
v a l u e s d e c r e a s e d s i g n i f i c a n t l y (PC.01) fr o m J u n e t o A u g u st f o r a l l
b r e e d s w i t h t h e I S3H, 3S1H, SH, HH, and AH d e c r e a s i n g by 14 .2 , 13.8,
11.5, 9.9, and 7.6 kg r e s p e c t i v e l y . The a n a l y s i s of v a r ia n c e t a b l e f o r
m ilk p ro d u c tio n i s g iv en i n Appendix t a b l e 11.
Body M easurements
Mean body w e i g h t s and w t z h t r a t i o s d id n o t d i f f e r among t h e
b r e e d s u s e d i n 1984 (P > .1 0) ( T a b le 4). Body w e i g h t s f o r t h e HH, AH,
I S3 H,
3 SIH ,
a n d SH a v e r a g e d
53 5 ,
537 , 543 , 5 4 8 ,
a n d 564 k g
r e s p e c t i v e l y and w tzh t r a t i o averaged 4.14 kg/cm f o r a l l breeds.
w e ig h t and w tzht r a t i o in c r e a s e d (PC.OI) d u rin g June,
Body
J u ly and August
f o r a l l b r e e d s f r o m 528 t o 550, and 557 kg and fro m 4.03 t o 4.18, and
4.21 r e s p e c t i v e l y .
The a n a l y s i s o f v a ria n c e t a b l e f o r body w eight and
w tzh t r a t i o i s g iv en i n Appendix t a b l e 12.
31
Table 3 . 1984 A verage
b re e d s.
d a ily
m ilk p r o d u c t i o n
(k g /d )
fo r
fiv e
Breed
June
I S3 H
16.2 + 2.1
9.4 + 1.5
2 .0 + 2.0
9 .2 ±.
.9 a
HH
13.6
I .9
7 .4 + 1.5
3.7 + 2 .2
8.2 +
.9 a
AH
12.1 + I .7
6 .9 + 1.4
4.5 + 2 .4
7 .9 +
.9 a
SH
19.7 ± 2.3
14.2 + 1.6
8.2 + .1 .8
14.1 + 1 .Ob
3S1H
21 .2 + I .9
12.6 ± 1.4
7 .4 + 2 .2
13.8 +
Meanl
16.6 + 1 .5 a
10.1 +
5.2 + I .7°
±
J u lv
Aueust
.6b
Meanl
.8b
1Means fo llo w e d by a common is u p e r s c r i p t a r e s i m i l a r (P < .0 1 ).
Table 4. Body w e i g h t (BW) and w e i g h t : h e i g h t ( w t : h t ) r a t i o s f o r
breeds used i n 1983 and 1984.
1QR4
1Q81
BW
( kg)
BW
( kg)
HH
555 + I6 a
535 + IOa
4.08
AH
-
537 + IOa
4.22 + .05a
I S3 H
-
543 + 9a
4.14 + .05a
3S1H
562 + I4 a
548 + 9a
4.05 + .05a
564
4.21 + .0 6 a
Breed
SH
-
±
Ila
w t:h t
( kg/cm)
±
.0 6 a
^ Means w i t h i n a co lu m n f o l l o w e d by a common s u p e r s c r i p t a r e
s i m i l a r (P<.0 5 ) .
cow
32
Forage D i g e s t i b i l i t y
T a b le 5 i s a s u m m a tio n o f t h e a v e r a g e IVOMD f o r b o th y e a r s .
A v e rag e mean f o r a g e d i g e s t i b i l i t y i n 1983 was
h i g h e r (PC.05) t h a n
1984 b u t t h e m onth o f A ugust was a b o u t t h e same f o r b o th y e a r s . Low
r a i n f a l l coupled w ith in c r e a s e d a i r te m p e r a tu r e s which t y p i f i e d th e
1984 s e a s o n may h av e c o n t r i b u t e d t o t h e y e a r l y d i f f e r e n c e s .
The
e f f e c t s o f t e m p e r a t u r e and w a t e r s t r e s s on f o r a g e q u a l i t y h ave b e en
documented by Van S o est (1982). D i g e s t i b i l i t y d ecreased th roughout th e
sum m er f o r b o t h y e a r s ,
b u t d ro p p e d s i g n i f i c a n t l y (PC.01) o n ly i n
August when IVOMD was about 58%. Monthly d e c re a s e s i n d i g e s t i b i l i t y
w ere ex p ec te d a s th e f o r a g e m atured (K artch n er and Campbell, 1979).
The d i g e s t i b i l i t y v a lu e s r e p o r te d h e r e a r e somewhat h ig h e r th an
th o s e r e p o r te d by Kronberg (1983), b u t a r e s i m i l a r to th o s e review ed
by K artch n er and Campbell (1979) and Van Dyne (1980).
The d iscrep e n c y
betw een Kronberg's (1983) d i g e s t i b i l i t y v a lu e s and th e v a lu e s r e p o r te d
h e r e i n p r o b a b l y l i e s i n t h e m e th o d o f e x t r u s a p r e p a r a t i o n .
The
p re v io u s r e s e a r c h e r d r ie d e x tr u s a sam ples i n a f o r c e d - a i r d ry e r a t
40 C p r i o r to i n v i t r o a n a l y s i s .
Some m e n t i o n i s g i v e n c o n c e r n i n g
e x c e s s i v e h e a t d u r i n g d r y i n g o r l o s s o f s o l u b l e o r g a n i c p o r t i o n s of
th e fo r a g e (Kronberg, 1983).
C o n firm atio n of t h i s concern i s r e p o r te d
by P f i s t e r and B u r r i t t (1 985) who found t h a t o ven-drying e x tr u s a a t 40
C s ig n ific a n tly
in c re a se d
n e u tra l
d e t e r g e n t f i b e r (ADF), and l i g n i n ,
T h ese
in c re a s e s
d e terg en t
fib e r
(NDF),
a c id -
compared t o f r e e z e - d r i e d sam ples.
may be r e f l e c t e d
in
d i g e s t i b i l i t i e s found by Kronberg (1 9 8 3 ).
th e
lo w er
o rg a n ic m a tte r
F r e e z e - d r i e d e x t r u s a g ave
11% h i g h e r (PC.01) OMD v a l u e s t h a n o v e n - d r i e d (50 C) when s e l e c t e d
33
s a m p l e s w e re co m p ared u s i n g b o th d r y i n g t e c h n i q u e s f o r b o th
(A p p e n d ix t a b l e 13).
years
J o h n s o n e t a l . (1962) a s c i t e d by B u rn s (1981)
r e p o r te d a 7% r e d u c tio n i n IVOMD when a l f a l f a - b r o m e g r a s s m ix tu re was
d r i e d a t 65 C co m p ared t o f r e e z e - d r y i n g . A c o s ta and Kothmann (1978)
c o n c lu d e d t h a t oven d r y i n g (60 C) was n o t a s a t i s f a c t o r y m ethod f o r
d ry in g fo ra g e c o l l e c t e d from e s o p h o g e a l l y - f i s t u l a t e d a n im a ls , but t h a t
f r e e z e - d r i e d sam p les gave b e t t e r e s t i m a t e s o f chem ical com position.
Table 5. Monthly f o r a g e IVOMD :f o r two y e a r s .
Yearl
June
1983
70%a
I 984
6 4% a
Ju lv
67%a
Mean^
August
65%a
59%b
6 2% a
6 I %b
57 %b
1 Means w i t h i n a y e a r f o l l o w e d by a common s u p e r s c r i p t a r e
s i m i l i a r (P<.01);
^M eans w i t h i n t h e co lu m n f o l l o w e d by a common s u p e r s c r i p t a r e
s i m i l i a r (P<.05).
Comparison o f F e c al Output E s tim a te s Using th e Cr-Og Technique and
T o ta l C o lle c ti o n Methods.
-------Fecal outp u t f o r
dry 3SIH and HH cows was o v e r e s tim a te d by about
17% u s in g Cr2Og, i n com parison to t o t a l c o l l e c t i o n s u s in g f e c a l bags
(A p p e n d ix
ta b le
1 4 ).
K ronberg
(1983)
over e s tim a tio n of f e c a l o u tp u t u sin g
O v e re stim a tio n
of fe c a l
o u tp u t
a lso
re p o rte d
a
17%
Cr2 Og w i t h 3 SI H a n d HH cow s.
has
b e e n r e v i e w e d by v a r i o u s
r e s e a r c h e r s in c lu d in g R aleigh e t a l . (1 9 8 0 ), and C o r b e t t (1 9 8 1 ).
34
DISCUSSION
F a c to r s A ffe o tin g I n ta k e D iff e re n c e s W ithin and Between Breeds
Assuming t h a t th e fo ra g e consumed by d i f f e r e n t b reed s of c a t t l e
i s of th e same d i g e s t i b l e energy c o n c e n tr a tio n ,
th e n a n im a l v a r i a t i o n
w i t h i n and between breeds becomes paramount i n e x p la in g t h e v a r i a t i o n
i n intake.B um inant 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 , body w e i g h t , and
body c o n d i t i o n h a v e b e e n shown t o a f f e c t f o r a g e i n t a k e ( A l l i s o n ,
1985).
In o rd e r t o e x p la i n how th e s e f a c t o r s im p a c t i n t a k e ,
i t must
be r e a l i z e d t h a t t h e y a r e d y n am ic and som etim es i n t e r r e l a t e d .
Level o f m ilk p ro d u c tio n and i t s r e l a t i o n s h i p t o v o lu n ta r y i n t a k e
h as been d i f f i c u l t to q u a n tif y f o r th e g ra z in g cow.
This a s s o c i a t i o n
h as no t been d e fin e d because th e cause and e f f e c t r e l a t i o n s h i p i s not
c l e a r . I n a d d i t i o n , f a t m o b i l i z a t i o n t o p ro d u c e m i l k c o n fo u n d s t h e
r e l a t i o n s h i p between m ilk y i e l d and c a l o r i c in ta k e .
c o rre la tio n
c o e ffic ie n ts
g e n e r a lly low (B ines,
1976).
To t h i s e x te n t,
b e tw e e n m i l k y i e l d a n d DOM i n t a k e a r e
In t h i s s tu d y ,
th e w i th in - b r e e d p a r t i a l
r e g r e s s i o n c o e f f i c i e n t between m ilk y i e l d and in ta k e was n e g l i g i b l e
and n o n - s i g n i f i c a n t (PX10).
Johnson e t a l . (1 966) found t h a t th e two
v a r i a b l e s w e re i n t e r d e p e n d e n t w h ile w orking w ith l a c t a t i n g H o ls te in
cows.
Between b reed s o f d i f f e r e n t m ilk p ro d u c tio n a b i l i t y however, m ilk
p ro d u c tio n may have a s i g n i f i c a n t e f f e c t on fo r a g e i n t a k e .
Lusby e t
a l . (1976) found t h a t w h ile g ra z in g summer fo ra g e , l a c t a t i n g H o ls te in
cows consum ed a b o u t 3.5% BW/d w h i l e H e r e f o r d s consum ed a b o u t 2.5%
BW/d.
They a t t r i b u t e d t h e i n t a k e d i f f e r e n c e s t o an i n c r e a s e d m i l k
35
p ro d u c tio n of 5.0 k g /d f o r th e H o ls te i n cows.
R e s u lts from t h i s study-
show t h a t between b re e d s,
m ilk p ro d u c tio n accounted f o r a b o u t 60 % o f
th e v a r ia tio n in in ta k e .
Marsh e t a l . (1971) s t a t e d t h a t 45-75% o f
th e v a r i a t i o n i n d a ily f o r a g e i n t a k e f o r cows d i f f e r i n g i n m ilk y i e l d
and
b re e d in g
w as a t t r i b u t e d
to
le v e l
o f m i l k p r o d u c t i o n and
l i v e w e i g h t . Mean m i l k p r o d u c t i o n and i n t a k e w e re h i g h e s t f o r t h e SH
and 3S1H c o m p ared t o t h e HH, AH, and I S3H a n i m a l s ( T a b l e s 2 and 3 ).
Although 1S3H and AH mean m ilk p ro d u c tio n was s i m i l i a r (P<.01), i n t a k e
le v e ls
d iffe re d
b e tw e e n th e s e
b reed s.
C o n v e rse ly ,
AH a n d SH
r e p r e s e n te d th e w id e s t range i n m ilk p ro d u c tio n , y e t t h i e r in ta k e
l e v e l s w ere e s s e n t i a l l y th e same. Other f a c t o r s in c lu d in g body w eight,
f a t d e p o s it io n , rumen volume, and t i s s u e m o b i l i z a t i o n may a ls o play an
im p o r ta n t r o l e i n d e te rm in in g i n t a k e among breeds.
A lth o u g h body w e i g h t w as s i g n i f i c a n t i n e x p l a i n i n g w i t h i n and
b e tw e e n b r e e d v a r i a t i o n i n i n t a k e f o r 1984, t h e p a r i a l r e g r e s s i o n
c o e f f i c i e n t (-0.003) was to o low to be b i o l o g i c a l l y im p o r ta n t.
Bines
(1976) s t a t e d t h a t c o r r e l a t i o n s b e tw e e n body w e i g h t a n d i n t a k e a r e
g e n e ra lly
h ig h ,
b u t o th e r r e s e a r c h e r s have found t h a t
v a r i a b l e s w e r e u n r e l a t e d (J o h n s o n e t a l . ,
1 9 66).
th e
two
L a n g la n d s (1968)
s u g g e ste d t h a t w i t h i n a breed, i n t a k e was more c lo s e ly r e l a t e d t o age
th an
body
w e ig h t,
and t h a t
it
se e m s u n l i k e l y
th a t
any s i n g l e
r e l a t i o n s h i p e x i s t s when d i f f e r e n c e s i n l i v e w e i g h t r e s u l t fro m
d i f f e r e n c e s i n a g e , b r e e d o r p r e v i o u s l e v e l of n u t r i t i o n .
A rn o ld
(1 970) r e p o r t e d t h a t l i v e w e i g h t can be a p o o r i n d e x o f i n t a k e , even
when a cc o u n tin g f o r d i f f e r e n c e s i n p r o d u c t i v i t y .
The amount of body f a t i n ru m in a n ts may i n f l u e n c e i n t a k e e i t h e r
36
c h e m o sta tic a lly
( F o r b e s , 1 980)
or
by p h y s i c a l l y
re d u c in g t h e i r
d i g e s t i v e c a p a c i t y (B a lc h and C a m p lin g , 1962; B i n e s , 1971). W trh t
r a t i o may be u sed a s an i n d e x t o body c o n d i t i o n ( K l o s t e r m a n e t a l . ,
1979).
The w ith in - b r e e d p a r t i a l r e g r e s s i o n c o e f f i c i e n t between w trh t
r a t i o a n d i n t a k e f o r t h i s s tu d y was - 0 . 3 1 .
N eg ativ e r e l a t i o n s h i p s
b e tw e e n body c o n d i t i o n and i n t a k e h av e a l s o b e en r e p o r t e d by A rn o ld
(1 9 6 4 ) , B a lc h and C am p lin g (1962) and N u t t e t a l . (1 9 8 0 ).
N u tt e t a l .
p a s t u r e s (DMD o f
( 1980) fo u n d t h a t f o r
5 5 %),
cows g r a z i n g lo w q u a l i t y
a s ig n if ic a n t p o s itiv e re la tio n s h ip e x iste d
betw een rumen c a p a c ity and f o r a g e i n t a k e (P<.06).
However,
f o r cows
g r a z i n g h i g h q u a l i t y p a s t u r e s (60% DMD), t h e r e w as no r e l a t i o n s h i p .
I n a d d i t i o n , they showed t h a t rumen c a p a c ity was p o s i t i v e l y r e l a t e d to
s tru c tu ra l
w e ig h t.
siz e ,
b u t n o t when e x p r e s s e d a s a p e r c e n t a g e o f body
S tru c tu ra lly
la rg e r
cows t e n d e d
to have l a r g e r
rum en
c a p a c i t i e s th a n s t r u c t u r a l l y sm a ll cows, but f a t t e r cows g e n e r a lly had
s m a l l e r ru m e n s t h a n t h i n cow s. D i f f e r e n c e s i n t h e am ount o f t o t a l
d i s s e c t e d f a t and s t r u c t u r a l d i m e n s i o n s b e tw e e n v a r i o u s b r e e d s o f
c a t t l e have been documented by C h arles and Johnson (1976) and th e ARS
\
(1975). I f r e a l d i f f e r e n c e s i n body c o m p o sitio n a n d /o r s t r u c t u r a l s i z e
do i n f a c t e x i s t between th e b reed s d i f f e r i n g i n m ilk p ro d u c tio n , th e n
t h e a s s o c i a t e d rumen volume w i t h i n th e s e groups may im pact th e amount
o f f o r a g e t h a t can be consum ed a s d i g e s t i b i l i t y d e c r e a s e s . R um inal
h y p e rtro p h y d u rin g l a c t a t i o n may a l s o have an im p o r ta n t in f l u e n c e on
d i g e s t i v e c a p a c i t y . F e l l and Weeks (1975) p r o p o s e d t h a t h y p e r t r o p h y
c o u l d be a r e s p o n s e t o some e n d o c r i n o l o g i c a l s t i m u l u s ,
p o ssib ly
l a c t o g e n i c h o rm o n e s . I t i s c o n c e i v a b l e t h a t l e v e l o f m i l k y i e l d may
37
d i c t a t e t h e r a t e o f h o rm o n a l s e c r e t i o n t h u s p r o m o t i n g a p a r t i c u l a r
h y p e rtro p h ic r e s p o n s e .
F orage D i g e s t i b i l i t y and I n t a k e
Mean in t a k e v a lu e s f o r th e HH and 3S1H breeds a r e rev iew ed a c r o s s
b o t h y e a r s i n t a b l e 6 . When sum m er f o r a g e d i g e s t i b i l i t y was 65%,
i n t a k e a s a p e r c e n t o f body w e i g h t b e tw e e n t h e HH and 3S1H w e re
sim ilia r,
b u t when f o r a g e d i g e s t i b i l i t y d e c l i n e d t o 61% t h e 3 SIH
consumed s i g n i f i c a n t l y more th a n t h e HH (P<.Q7). In ta k e f o r th e HH was
2.3% BW/d i n 1984 when OMD was 61%, b u t i n 1983 when OMD was 65%,
t h e i r i n t a k e i n c r e a s e d (P<.07) t o 2.8% BW/d.
C o m p a r a t i v e l y , 3 SI H
i n t a k e w as a b o u t 2.8% BW/d f o r b o th y e a r s .
Table 6 . A verage d a i l y i n t a k e (% BW 0MB) f o r two b r e e d s o v e r
both f i e l d s e a s o n s .
Breed^
Year -x
OM&L
HH
1983
65%&
2 .8 a
2 .7 a
1984
6l%b
2 .3 b
2 .8 *
3S1H
«1
Means w i t h i n the column f o ll lo w e d by a common s u p e r s c r i p t a r e
s i m i l i a r (P<.05).
^Means w i t h i n a row or column fo llo w e d by a common s u p e r s c r i p t
a r e s i m i l a r ' (P<.07).
K ro n b e rg (1983) r e p o r t e d t h a t when f o r a g e OMD a v e r a g e d 50% i n
1982, HH i n t a k e was 1.9% BW/d w h ile 3S1H i n t a k e was h ig h e r (P<.10) a t
2.1% BW/d. Across a l l t h r e e y e a r s , when monthly fo rag e OMD approached
38
57%, in ta k e f o r th e HH and 3S1.H b reed s was a p p ro x im a te ly 2.1 and 2.4%
BW/d r e s p e c t i v e l y . K loseterm an e t a l . (1979) i n d i c a t e d t h a t a s f o r a g e
q u a lity decreased,
C h a r o l a i s t y p e cows a t e m ore p e r u n i t o f body
w e i g h t t h a n Angus ty p e cow s.
The i n t a k e a n a l y s i s o f v a r i a n c e t a b l e
f o r t h e HH and 3S1H b r e e d s f o r b o th y e a r s i s g i v e n i n A ppendix t a b l e
15.
For d i e t s between 52 and 66% d i g e s t i b i l i t y ,
Conrad e t a l . (1964)
a s c i t e d by B ra u m g a r d t (1970) fo u n d t h a t f e e d i n t a k e i n c r e a s e d w i t h
in c re a sin g
d ig e stib ility
b o d y w ie g h t
(re fle c tin g
and t h e
fa c to rs
c ap a c ity ),
lim itin g
u n d ig e ste d
b o d y w ie g h t p e r day ( r e f l e c t i n g r a t e
in ta k e
re sid u e
per
w e re
u n it
o f p a s s a g e ) , and d ry m a t t e r
d i g e s t i b i l i t y . For d i e t s between 67 and 80% d i g e s t i b i l i t y , fe e d i n t a k e
d e c re a se d w ith in c r e a s i n g d i g e s t i b i l i t y ( c o n tr o l of energy in ta k e ) and
i n t a k e a p p e a r e d t o be d e p e n d e n t on m e t a b o l i c s i z e ,
d ig e stib ility .
p r o d u c t i o n and
M ontgomery and B r a u r m g a r d t ( 1965b) s u g g e s t e d t h a t
f o r a g e i n t a k e o f d a i r y cows i s l i m i t e d by rum en c a p a c i t y when th e y
consume d i e t s w ith l e s s th a n 67% DM d i g e s t i b i l i t y . N utt e t a l . (1980)
found
th a t
p h y s ic a l f a c t o r s a p p a r e n tly lim it e d i n t a k e
o f Ia c tatL n g
Angus cow s w hen f o r a g e DM d ig e s t ib ility a v e r a g e d 55%, b u t w e re n o t
i m p o r t a n t f o r cows g ra z in g p a s tu r e s a v e r a g in g 60% DM d ig e s tib ility . In
a d d itio n ,
th e
p o in t w h e re p h y s ic a l li m i t a t i o n s t o i n t a k e
c e a se
and
m e ta b o lic p ro c e s s e s b e g in to d o m in a te may v a ry w ith milk p ro d u c tio n so
t h a t b re e d s v a ry in g i n milk y ie ld may h a v e d i f f e r e n t t r a n s i t i o n p o in ts
( Conrad e t a l., 1964). S in ce i n t a k e f o r t h e 3S1H re m a in e d e s s e n tia lly
t h e sam e w hen s e a s o n a l f o r a g e OMD c h a n g e d from 6 1 to 65%, and HH
i n t a k e i n c r e a s e d from
2.3 t o 2.8%
BW/d,
t h e 3 S 1 H may r e a c h
th e
39
t r a n s i t i o n b e tw e e n g u t fa ll and e n e rg y r e g u la tio n a t a lo w e r l e v e l of
d ig e s t ib ility .
This in c o n t r a s t t o r e s u l t s from
Conrad e t a l.
(196 4)
which show ed t h a t f o r dairy cow s p ro d u c in g 13 kg malk/d t h e p o in t
b e tw e e n g u t fall and m e ta b o lic c o n tr o l w as a t a p p ro x im a te ly 65% 0 MD.
For cows producing 27 kg malk/d th e le v e l was raised to about 70% OMD.
Monthly d e c r e a s e s i n f o r a g e i n t a k e
e v id e n t i n both y e a r s .
(P<.01), from
In 1 983,
w ith
d e clin in g
OMD a r e
when f o r a g e d ig e s tib ility d e c r e a s e d
67% i n July to 59% i n August, m ean i n t a k e f o r both th e
3S1 H and HH cow s d e c r e a s e d (P<.07) from 3.0 to 2.3 % BW/d. In 1 984,
w hen f o r a g e d ig e s tib ility d e c r e a s e d from 64 to 62%, a v e r a g e i n t a k e f o r
th e fiv e
breeds
d e clin ed
d ig e stib ility
d ecreased
c o n tin u e d to
decrease
(P < .0 5) fro m
2 .9 t o 2 .4 % B W /d.
even f u r t h e r in
a lth o u g h
A ugust to
not sig n ific a n tly .
s u g g e s t t h a t sm all c h a n g e s i n d i g e s t i b i l i t y
d ifferen c es in in ta k e .
Holloway
e t a l.
5 8%,
When
in ta k e
T h is s e e m s t o
may i n d u c e
sig n ific a n t
(197 9) fo u n d t h a t l a c t a t i n g
Angus cows grazing pasture th a t was 60.8% DMD consumed 1.7 kg/d more
(P<«01) dry m a tte r t h a n cow s g ra z in g 58.3% DMD p a s tu r e , a d if f e r e n c e
o f 2.5 p e r c e n ta g e u n its .
Van S o e s t (196 5) s u g g e s te d t h a t c e ll w all c o n s t i t u e n t s or t h e
f i b e r mass of f o r a g e s i s in v e r s e ly r e l a t e d t o v o lu n ta ry i n t a k e .
As a
p la n t m a tu re s, t h e p e r c e n t of t o t a l fib r o u s p a r t s i n c r e a s e . When th e s e
c o n s t i t u e n t s i n c r e a s e t o more th a n 55 to 60% of th e dry m a tte r , i n t a k e
b e co m e s l im it e d . R a th e r th a n consuming m ore f o r a g e w hen d ig e s tib ility
i s low ( to a c h ie v e a g iv en e n erg y i n t a k e ) , g ra z in g r u m i n a n ts te n d to
consum e le s s fo ra g e
H o w ev er,
w hen d ig e s tib ility
d e re a s e s (W a llac e 1984).
Ellis (197 8) c a u tio n s t h a t d ig e s tib ility of t h e f o r a g e
does
40
n o t a p p e a r to
be a n a b s o l u t e
su g g ested
d ig e stib ility i s
th a t
p re d ic to r
a
of v o lu n ta ry in ta k e .
d y n a m ic
process
w hich i s
th e
He
net
r e s u l t o f tw o r a t e s ,
d i g e s t i o n a n d p a s s a g e o f f e e d a n d c o u ld a f f e c t
v o lu n ta ry in ta k e in
e ith e r a p o sitiv e ,
n e g a tiv e ,
or in d e p e n d e n t
f a s h i o n . I n c o n c l u s i o n h e p o i n t e d o u t t h e n e e d f o r m e a s u r in g r a t e s o f
d i g e s t i o n and p a r t i c l e s i z e d e g r e d a t i o n , b u lk volume p e r u n i t of t o t a l
cell
w a ll c o n s t i t u e n t s
of th e fo ra g e
c o m p ris in g f i l l ,
and fra g m e n ta tio n
p ro p e rtie s
on c o n s u m p t io n a n d s u b s e q u e n t f e r m e n t a t i v e
d ig e stio n
r e l a t i v e t o t h a t r e q u i r e d f o r p a s s a g e from t h e r e t i c u l o - rumen.
P r e l i m i n a r y E f f i c i e n c y E v a l u a ti o n s
A lo n g -te rm
e ffic ien cy
o b je c tiv e of th is stu d y is to a sse ss t h e in p u t/o u tp u t
of ra n g e la n d
I n f o r m a t i o n on t h e
b e e f co w s d i f f e r i n g i n
milk p r o d u c t i o n ,
p ro d u c tiv e
p o te n tial.
c a l f p e r f o r m a n c e an d r e b r e e d i n g
s u c c e s s o f t h e s e b r e e d t y p e s w ill c o n t i n u e to b e r e c o r d e d an d c o m p a r e d
w ith
th e ir fo rag e
e ffic ie n c y .
in ta k e
to
d ev elo p
an
in d e x
to
th e ir
o v e ra ll
T h e s e i n d i c e s w ill be u s e d only t o d e p i c t a r e l a t i o n s h i p
b e tw e e n p ro d u c tio n and in ta k e ,
d if f e r e n c e s in fo r a g e q u a lity
h a v e a n a f f e c t on b r e e d
an d n o t a s a b s o l u t e v a l u e s .
Y e a rly
o r o t h e r e n v i r o n m e n t a l i n f l u e n c e s may
g ro u p e f f i c i e n c y such t h a t t h e r e l a t i o n s h i p
betw een i n t a k e and e f f i c i e n c y may ch an g e .
P r e li m in a r y d a t a fro m 2 y e a r s h a s s h o w n t h a t 3S1 H r e q u i r e d
an
a v e r a g e o f 1.1 k g o f f o r a g e p e r k g milk p r o d u c e d a n d HH r e q u i r e d 1.3
kg o f f o r a g e .
D a ta t a k e n fro m K r o n b e r g (1983) s h o w e d t h a t d u r in g t h e
s u m m e r s e a s o n o f 1 982, b o th t h e 3 SI H a n d HH c o n s u m e d a b o u t 1.1 k g
f o r a g e p e r kg m ilk. I n 1 984, milk p r o d u c t i o n e f f i c i e n c y f o r t h e 3S1 H
41
re m a in e d u n c h a n g e d , but t h e HH consum ed .4 kg more f o r a g e p e r kg milk
p ro d u c e d . The li m i t e d n um ber of a n im a ls in v o lv e d i n t h e s e e f fic ie n c y
e v a lu a tio n s , com bined w ith y e a r ly e n v iro n m e n ta l d i f f e r e n c e s , p re c lu d e s
c o n c lu sio n s r e g a r d in g th e i n p u t / o u t p u t e f f ic ie n c y of t h e 3S1 H and HH
b re e d s.
The t e n t a t i v e i n f o r m a t io n p r e s e n te d h e r e i s i n t e n d e d t o be
b u ilt upon t o m ore fu lly u n d e rs ta n d th e i n t e r a c t i o n b e tw e e n y e a r and
b reed
c h a ra c te ristic s.
H o llo w a y
and
B u tts
( 1983)
n o te d
th a t
d i f f e r e n c e s i n f o r a g e q u a lity a f f e c t e d t h e e f f ic ie n c y of c o n v e rsio n of
d ig e s tib le
DM i n t a k e
to
c a l f g a in f o r
cow s d if f e r in g i n s t r u c t u r a l
s iz e . On h ig h q u a lity f e s c u e - le g u m e p a s tu r e s , s t r u c t u r a l s iz e was n o t
re la te d to efficien cy ,
bu t on lo w e r q u a lity fe s c u e p a s tu r e s ,
sm aller
cows ten d ed to be th e most e f f i c i e n t .
Appendix t a b l e 16
a t t e m p t s t o i l l u s t r a t e t h e r e l a t i v e s p re a d i n
i n t a k e f o r th e b re e d s used i n 19 84 by co m p arin g them t o t h e I S3 H.
T e n ta tiv e
e ffic ie n cy
d a ta
p ro d u c tio n and c a lf ADG.
simply
used t o
in ta k e .
co m p are
are
a ls o
p ro v id e d in
te rm s
of
m ilk
Milk p ro d u c tio n and c a lf g a in i n d ic e s a re
each
b r e e d 's p ro d u c tio n i n t a k e
A h ig h e r in d e x d e n o te s a g r e a t e r q u a n tity
a g a in s t i t s
of o u t p u t v e rs u s
i n p u t . Although t h e 3S1 H h a v e a high milk p r o d u c tio n in d e x , th e y h av e
t h e lo w e s t c a lf g a in in d e x .
More r e s e a r c h i s n e c e s s a ry to d e te rm in e
th e maintenance demands of these cows in a free-ran g in g environment in
o rd e r t o e s ti m a te t h a t p o rtio n of i n t a k e going t o milk p ro d u c tio n . In
a d d itio n ,
c a lf,
l i t t l e i s known a b o u t t h e
and stu d ie s are
n u t r i t i o n a l r e q u ir e m e n ts o f th e
needed to le n d in s ig h t in to
b e h a v io r i n a ra n g e s e t t i n g .
c a lf
g ra z in g
42
SUMMARY
The fe e d e f f i c i e n c y of v a rio u s b eef cow breed ty p e s d i f f e r i n g i n
m ilk p ro d u c tio n ,
body s i z e o r body c o m p o s i t i o n i s
a concern to
l i v e s t o c k o p e r a t o r s w is h in g t o o p tim iz e b eef p ro d u c tio n from th e range
resource.
In o rd e r to u l t i m a t e l y i d e n t i f y t h e p r o d u c t i v e p o t e n t i a l
and a d a p t i b i l i t y
of th e se v a rio u s b reed s to a p a r t i c u l a r g ra z in g
e n v i r o n m e n t i t i s n e c e s s a r y t o e s t i m a t e t h e i r f o r a g e c o n s u m p tio n .
L e v e l o f m i l k y i e l d may a c c o u n t f o r t h e m a j o r i t y o f t h e i n t a k e
d i f f e r e n c e s b e tw e e n b r e e d s ,
b u t m e a s u r e m e n ts o f body s i z e ,
fat
d e p o s i t i o n and rum en v o lu m e may a l s o be u s e f u l i n f u r t h e r d e f i n i n g
th o s e f a c t o r s i n f l u e n c i n g fo ra g e consumption.
D iff e re n c e s i n seaso n al
fo ra g e OMD may a ls o a f f e c t i n t a k e d i f f e r e n c e s between b reed s.
when f o r a g e OMD was 65%,
In 1983
i n t a k e d i f f e r e n c e s p e r u n i t o f body w e i g h t
between HH and 3S1H cows w ere d im in is h e d compared t o in t a k e l e v e l s a t
61% OMD. As fo r a g e OMD i n c r e a s e s , th e f a c t o r s t h a t c o n tr o l i n t a k e may
be
d iffe re n t
th a n th o se
c o n tro llin g
in ta k e
a t lo w e r l e v e l s
of
d i g e s t i b i l i t y . The t r a n s i t i o n p o in t betw een r e g u l a t i n g mechanisms may
vary w ith breed a s w e l l .
M ilk p r o d u c t i o n , c a l f p e r f o r m a n c e and r e p r o d u c tiv e perform ance
should c o n tin u e to be t e s t e d i n r e l a t i o n t o fo ra g e i n t a k e to develop
in d e x in g r a t i o s of th e o v e r a l l e f f i c i e n c y of th e breed ty p e s on n a t i v e
ra n g e la n d s .
F u t u r e r e s e a r c h a r e a s t h a t may be u s e f u l i n f u r t h e r d e f i n i n g
th o s e f a c t o r s i n f l u e n c i n g i n ta k e a r e (I) Measurements of rumen volume
u s i n g t h e d i l u t i o n t e c h n i q u e w i t h a l i q u i d m a r k e r t o be c o r r e l a t e d
43
w i t h l i n e a r m e a s u r e m e n ts o f s t r u c t u r a l s i z e . (2) A n a l y s i s o f f o r a g e
c e l l w a ll c o n te n t from e x tr u s a sam ples.
x
\
44
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P ro c .
APPENDIX
Table 7. Intake values fo r various breeds of grazing cows using the chromic oxide method fo r fecal output.
Body
Weight
(ke)
Milk
Production
kg/d
Intake
(SBW)
Forage D ig e s tib ility /
Technicue
Reference
Breed
Brumby, 1959
Jersey
Fresian
397
526
8.6
13.1
3.0 OM
3.0 OM
Corbett e t a l . , 1963
Ayrshire
430
14.6
1.9 OM
74% OMD/FN
H ills , 1968
Hereford
Santa Gertrudis
380
441
-
3.0 OM
2.7 OM
57.9* OMD/LR
54.9* OMD/LR
Holloway e t a l . , 1979
Angus
457
472
8.5
8.3
1.9 DM
2.2 DM
58* DMD/ADL
61* DMD/ADL
Hollcway & B utts, 1983
Angus
442
438
5.4
5.8
1.8 DM
2.2 DM
59* DMD/ADL
64* DMD/ADL
Jones e t a l . , 1965
Ayrshire
494
479
12.7
17.5
2.8 OM
3.0 OM
77* OMD/FN
78* OMD/FN
Lusby e t a l . , 1976
Holstein
Hereford x Holstein
Hereford
458
372
360
—
3.5 DM
2.5 DM
2.5 DM
62* DtWin Vitro
62* DMD/in Vitro
62* DMD/in Vitro
Nutt e t a l . , 1980
Angus
465
496
6.5
7.5
1.7 DM
1.9 DM
55* DMD/ADL
59* DMD/ADL
S tr e e te r e t a l . , 1974
Brcwn Swiss
Charolais x Angus
Hereford
474
375
371
10.3
7.5
6.0
3.1 DM
3.2 DM
2.8 DM
59* CWCD/in Vitro
59* CWCD/in Vitro
59* CWCD/in Vitro
_
—
——
54
T ab le 8 . L e a s t s q u a r e s a n a l y s i s o f v a r i a n c e o f o r g a n ic m a t t e r i n t a k e
(OMI) 1983.
df
Mean Squares
OMI
(% BW/d)
Breed
Month
Breed x month
Sex o f c a l f
S ir e breed of c a l f
I
2
2
I
I
0.011
0.692***
0.124
0.008
0
R eg ressio n
Age of c a l f
Body w eight
I
I
0.006
0.091
23
0.061
Source
R esidual
R2
0.86
***?<.01
Table 9 . L e a s t s q u a r e s a n a l y s i s o f v a r i a n c e f o r body w e i g h t (BW)
1983.
Source
df
Breed
Month
Breed x month
Sex o f c a l f
S ir e breed of c a l f
I
2
2
I
I
R eg ressio n
Age of c a l f
I
R esid u al
R2
**«P<.01
*P< .05
24
Mean Squares
OMI
(% BW/d)
433.2
8318.5**
33.7
4.8
802.8
25526.0
2413.3***
0.49
55
T ab le 10. L e a s t s q u a r e s a n a l y s i s o f v a r i a n c e of o r g a n i c m a t t e r i n t a k e
(OMI) 1984.
Source
df
Mean Squares
OMI
(% BW/d)
Breed
Month
Breed x month
Sex o f c a l f
S i r e breed of c a l f
4
2
8
I
I
0.648***
0.230*
0.032
0
0.338**
R eg ressio n
Age of c a l f
Milk p ro d u c tio n
Wt:Ht r a t i o
Body w eight
I
I
I
I
0.086
0.167
0.434**
I .003***
R esidual
R2
***?<.01
**P<.05
*P<.06
69
0.078
0.77
56
Table 11. L east sq u a re s a n a l y s i s o f v a ria n c e of m ilk p ro d u c tio n (MP)
1984.
df
Mean Squares
MP
(kg/d)
Breed
Month
Breed x month
Sex o f c a l f
S ir e breed of c a l f
4
2
8
I
I
128.1***
107.7***
13.2
41 .7*
70.8**
R egression
C alf age
I
10.6
72
11.6
Source
R esid u al
R2
0.68
***P<.01
**P<.05
*P<.10
Table 12. L east sq u ares a n a l y s i s of v a ria n c e of body w eight (BW) and
w eight :h e ig h t r a t i o (w t:h t) 1984.
Mean Squares
Source
df
BW
(kg)
Wt :Ht
(kg/cm)
Breed
Month
Breed x month
Sex o f c a l f
S ir e breed of c a l f
4
2
8
I
I
R egression
Age of c a l f
I
368.7
0.014
72
1364.2
0.053
R esid u al
R2
***P<.01
1355.1
11917.9'***
99.6
1716.9
598.7
0.32
0.087
0.697***
0.006
0.003
0.014
0.36
57
Table 13. Comparison of OMD betw een s e le c te d sam p les o f e x tru s a
u sin g two d ry in g m ethods1.
Month
IQgR
F re e z e -d rie d O ven-dried
IQRH
F re e z e -d rie d
O ven-dried
June
69%a
63%*
71%*
62%b
J u ly
69%*
63%b
62%a
55%b
August
6l% a
52%b
59%*
O
LO
Mean*
66%a
59%b
6H%a
56%b
1 Means w i t h i n a y e a r w i t h i n a m onth f o llo w e d
s u p e r s c r i p t a r e s i m i l i a r (P<.07).
* P C . 01
by a common
Table 14. 1983 Fecal o u tp u t e s tim a te s f o r dry cows u sin g t o t a l c o lle c tio n and chrom ic o x id e (Cr2Oo)
te c h n iq u e s 1 .
^
Breed
June
T otal
c o lle c tio n
Cr2 O3
J u lv
T o tal
c o lle c tio n
Cr2 O3
August
T o tal
c o lle c tio n
Cr2 Og
Mean
T o tal
c o lle c tio n
Cr2 Og
HH
0.5
0 .7
0.6
0 .7
0 .7
0.6
0.6
0.7
3S1H
0 .5
0 .7
0.6
0.8
0.6
0.7
0.6
0.7
1 %BW OMB
59
T ab le 15. L e a s t s q u a r e s a n a l y s i s o f v a r i a n c e o f o r g a n ic m a t t e r i n t a k e
(OMI) f o r HH and 3S1H b r e e d s 1983 and 1984.
Source
df
Mean S quares
OMI
(.% BW/d)
Breed
Month
Year
Breed x y e a r
Breed x month x y e a r
Sex o f c a l f
S ir e breed of c a l f
I
2
I
I
6
I
2
0.624***
0.138
0.025
0.849***
0.296***
0.104
0 .078
R eg ressio n
Age of c a l f
I
0.450**
R esid u al
R2
*«*P<.01
**P< .05
53
0.082
0.79
Table 16. In ta k e d if f e r e n c e s and e f f ic ie n c y e v a lu a tio n s f o r b reed s used i n 1984
C alf ADG
(kg/500 kg BW)
C alf Gain
Index
.78
1 .14
.10
7 .6
.66
I .10
.09
+1 #6
7 .3
.58
1 .08
.09
564
+2.1
12.6
.96
1 .11
.09
548
+3.4
12.6
.88
1 .18
CO
O
Breed
BW
(kg)
kg/d/500
kg BW
Milk p ro d u c tio n
(k g /d /5 0 0 kg BW)
1S3H
543
10.9
8.5
HH
535
+0.6
AH
537
SH
3S1H
M ilk P ro d u c tio n Index= MPZcSOO kg BW
I n t a k e / 500 kg BW
C alf Gain Index= C alf ADG/500 kg BW
In ta k e /5 0 0 kg BW
Milk P ro d u ctio n
Index
61
T ab le 17. L e a s t s q u a r e s a n a l y s i s o f v a r i a n c e
m a t t e r d i g e s t i b i l i t y (IVOMD).
Source
Month
Year
Month x y e a r
R esid u al
R2
***?<.01
**P<.05
df
2
I
2
63
of in v i t r o
o rg a n ic
Mean Squares
IVOMD
329.4***
156.5**
25.7
38.7
0.27
M ON TA N A S T A T E U N IV E R S IT Y L IB R A R IE S
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Forage in ta k e and m ilk
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