Winter foraging behaviors of beef cows in relation to acute thermal stresses and supplementation
by Steven Kenneth Beverlin
A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in
Range Science
Montana State University
© Copyright by Steven Kenneth Beverlin (1988)
Abstract:
Two trials were conducted during the winters of 1986 and 1987. Trial 1 began December 15, 1985 and
ended March 6, 1986. Trial 2 was initiated December 15, 1986 and concluded February 28, 1987.
Objectives were (1) to determine range forage intake and grazing behavior responses of prepartum beef
cows to supplementation and winter environmental conditions and (2) to determine acclimation lengths
of winter foraging strategies for free-roaming pregnant beef cattle under short term-thermal and
wind-chill stresses. In 1986, 61 cows of Hereford X Angus and (or) Tarentaise genotypes were used.
Cows were stratified within five supplement groups: soybean meal (SEM), bloodmeal (BM), com
gluten meal (CGM), animal fat (FAT) and range forage only (CON). SBM, CGM, EM, and FAT
received 200 g/d rumen degradable protein. EM and OGM received 200 g/d additional bypass protein
and FAT received 50 g/d additional bypass energy. Two groups of ten cows wore fecal bags for a week
in January and February. Rectal grab samples were obtained from all 61 cows concurrently with total
fecal collections. Four groups of four cows wore vibracorders to estimate daily grazing time in three
intervals: 0701-1300, 1301-1900 and 1901-0700 and pedometers to estimate distance travelled per day.
There were no differences (P<.05) in forage organic matter intake (OMI), daily grazing times (DGT),
grazing tine per interval (DGTI) or distance travelled per day (DT). Supplemented cows lost less
weight and condition (P<.05,-14.5 kg, -.68) than CON (-44.4 kg, -.95), respectively. OMI and DGT
were expressed within a narrow potential range under low forage quality and mild environmental
conditions. In 1987, 16 cows of the same genotype as trial 1 wore vibracorders and pedometers using
the same methods as trial 1. Four groups of four cows wore fecal bags for 96 h collections within a
week in January and February. Rectal grab samples were obtained daily from all cows. All cows were
bolused daily with 10 g chromic oxide. Acclimation lengths were determined for daily OMI, DGT, and
DGTI under short-term thermal stress (STTS) and wind-chill temperature (WCT). Acclimation lengths
of I to 3 days increased CME (P<.05) and decreased DGT (P<.05) to both STTS and WCT. DGTI
showed variable responses. Generally, larger DGTI responses were associated with longer acclimation
lengths. Cows returned to normal CMI and DGT regimes within 72 h. The presence of fecal bags
decreased DGT by 24.2 minutes (P<.001). Grazing times from 1301-0700 were unaffected (P>.05).
From 0701-1300 grazing times were decreased 10.7 minutes (P<.001) by presence of fecal bags due to
bags being full before being changed prior to 1130 h. Adjustment factors should be made for animals
wearing fecal bags until a more suitable method for free-roaming conditions becomes available. WINTER FORAGING BEHAVIORS OF BEEF COWS IN RELATION TO
ACUTE THERMAL STRESSES AND SUPPLEMENTATION
by
Steven Kenneth Beverlin
A thesis submitted in partial fulfillment
of the requirements for the degree
of
Master of Science
in
Range Science
MONTANA STATE UNIVERSITY
Bozeman, Montana
April 1988
/3 IUS
ii
APPROVAL
of a thesis submitted by
Steven Kenneth Beverlin
This thesis has been read by each member of the thesis committee
and has been found to be satisfactory regarding content, English usage,
format, citations, bibliographic style, and consistency, and is ready
for submission to the College of Graduate Studies.
Approved for the Major Department
H
Date
- V
- V l '%
O
-
T"
v
Approved for the College of Graduate Studies
Date
\
>
Head, Major Department
Graduate Dean
'XV'M>-.
iii
STATEMENT OF PERMISSION TO USE
In
presenting
this
thesis
in
partial
fulfillment
of
the
requirements for a master's degree at Montana State University, I agree
that the Library shall make it available to borrowers under rules of
the Library.
Brief quotations from this thesis are allowable without
special permission, provided that accurate acknowledgment of source is
made.
Permission for extensive quotation from or reproduction of this
thesis may be granted by my
major professor, or in his/her absence, by
the Dean of Libraries when, in the opinion of either, the proposed use
of the material is for scholarly purposes.,Any copying of use of the
material in this thesis for financial gain shall not be allowed without
my written permission.
iv
ACKNOWLEDGEMENTS
Many people
project.
have
assisted with
the
completion
People of significant importance include:
Eldon Ayers,
Ed Fredrickson,
of this
thesis
Dr. Kris Havstad,
Pete Olind and Russell Mack.
Without
their advice, assistance, bad jokes, and comradeship none of this would
have happened. . The next "Master Bagger" world championships are in
South Dakota with bison!
John Lacey,
Sincere thanks also go to Drs. Mark Petersen,
Jack Taylor,
Brian Sindelar, and Clayton Marlow whose
valuable advice made things easier on everyone.
Kachman, Kathy Hanford,
kept me "on line".
Thanks also to Steve
and Carol Bittinger whose computer expertise
To everyone at the Nutrition Center, especially Dr.
Nancy Roth and Connie Clark, thanks for the help and assistance.
the
secretaries,
Gayle,
Pat,
Diane,
Jo,
and Jeanne:
"thanks
To
for
letting things slide".
Much of the credit for completing this project goes to my family:
Mom and Dad,
overwhelming a
burdens.
Dave and Jill,
call home
and Mike
always
Beverlin.
improved my
When things got
spirits
and eased my
Thanks!
Most of all, love and gratitude goes to. Gail for putting up with
thirty hour stints on the computer, all night sessions at the Nutrition
Center and the fragrant smells of rumen extrusa and cow s__t.
Your
love and companionship made all it worthwhile.
My heartfelt thanks to all of you for making this journey possible.
V
TABLE OF CONTENTS
Page
LEST OF TABLES.................................................... vii
ABSTRACT.... .............................................. ........
ix
INTRODUCTION......................................................
I
LITERATURE REVIEW.................................................
3
Introduction..................................................
Heat Production and Metabolism................................
Winter Foraging Strategies....................................
Digestive Responses.............. *.......... .................
Supplementation...............................................
Pregnancy......................
3
5
7
11
14
18
MATERIALS AND METHODS.............................................
21
Study Site.............................
Animals...................... ...................... ........
Treatments...............
Measurements...........................................
Grazing Behavior..........
Fecal Organic Matter Output..............................
Dietary Digestibility.............
Forage Organic Matter Intake.............
Body Weight and Condition Score."..........
Climatic Conditions......................................
Data Analyses.................................................
Trial I, 1986....
Trial 2, 1987............................ ..............
21
22
22
24
24
25
26
'28
29
29
29
29
30
RESULTS..........
33
Trial I, 1986.........................
Forage Intake...................................
Grazing Behavior................................
Calf Birthweight, CowBody Weight and Condition Score.....
Climatic Conditions......................................
33
33
34
35
36
Trial 2, 1987.................................................
Forage Intake..............
Grazing Behavior.............. ........................*..
Influence of Fecal Bagson Daily Grazing Times............
37
37
39
42
vi
TABLE OF CONTENTS - Continued
Page
DISCUSSION.......................
43
Trial I, 1986............................................
Forage Intake....................
Grazing Behavior... .....................................
Calf Birthweight, Cow Body Weight and Condition Score....
43
43
45
47
Trial 2, 1987.........
Forage Intake............................................
Daily Grazing Time.......................................
Influence of Fecal Bags on Daily Grazing Time............
48
49
52
54
SUMMARY................... '.................... .... '..............
57
RECOMMENDATIONS.... ......................
5g
REFERENCES CITED..............
62
APPENDIX........................................
73
vii
U S T OF TABLES
Table
Page
1. Supplement cxmposition (g/d), Trial I................. ........
23
2. Estimation of fecal output (PO, kg) and forage organic
matter intake (CM! %E$V, OMB) from rectal grab samples.
Trials I and 2...................................
28
3. Forage organic matter intake (CM! %BW, OMB) for each
supplement. Trial I .......... ................................
33
4. Daily grazing time (h), grazing time per interval (h)
and distance travelled (km/d) for each supplement,
Trial I ....................
35
5. Calf bifthweight (kg), pre-calving cow body weight
change (kg) and condition score change for each supplement,
Trial I...........
36
6 . Average Ambient Temperature (C), long-term average, and
deviation from normal for each month, Trial I.................
37
7. Significant responses of daily forage organic matter
intake ( C M %BW, OMB) to short-term thermal stress and
magnitude of response (%BW) for acclimation lengths of
I to 20 days, Trial 2 .........................................
38
8 . Significant responses of daily forage organic matter
intake ( C M %BW, OMB) to wind-chill temperature and
magnitude of response (%BW) for acclimation lengths
of I to 20 days, Trial 2 ......................................
38
9. Significant responses of daily grazing times (h) to
short-term thermal stress and magnitude of response
(h) for acclimation lengths of I to 20 days, Trial 2 ..........
40
10. Significant responses of daily grazing times (h) to
wind-chill temperature and magnitude of response (h)
for acclimation lengths of I to 20 days, Trial 2..............
41
11. Influence of fecal bags on daily grazing times (h)
and magnitude of response (min), Trial 2 ...... ...■............
42
12. Chromic oxide analysis procedure, Trials I and 2 ... ...........
74 •
viii
U S T OF TART F-S-Continued
Table
.Page
13. Chromic oxide fed (g/d) and recovery (% as fed) from
total fecal collections and rectal grab samples for each
supplement. Trial I .......... ................................
75
14. Means for esophageal extrusa in vitro organic matter
digestibility (IVOMD) and crude protein (CP), Trial 1 .........
75
15. Daily fecal output (PO, %BW) estimated using total fecal
collections, Cr2O3 , and rectal grab samples for each
supplement. Trial 1 ...........................................
76
16. Initial, final and change in cow body weight (kg) and .
condition score for each supplement. Trial I....... ...........
76
17. Chromic oxide (Cr2O3) recovery (% as fed) per cow from
total fecal collections and rectal grab samples, Trial 2 .... .
77
18. In vitro organic matter digestibility (IVOMD) from rumen
extrusa for each week, Trial 2.................................
78
19. Fecal output (PO, %BW) for each cow for each week estimated
from rectal grab samples, Trial 2 .............................
79
20. Initial, final and change in cow body weight (kg) and
condition score. Trial 2 ............................ ..........
80
21. Distance travelled (kr^/d) for all cows, Trial 2 ...............
81
IX
ABSTRACT
Two trials were conducted during the winters of 1986 and 1987.
Trial I began December 15, 1985 and ended March 6 , 1986. Trial 2 was
initiated December 15,
1986 and concluded February 28,
1987.
Objectives were (I) to determine range forage intake and grazing
behavior responses of prepartum beef cows to supplementation and winter
environmental conditions and (2) to determine acclimation lengths of
winter foraging strategies for free-roaming pregnant beef cattle under
short term-thermal and wind-chill stresses.
In 1986, 61 cows of
Hereford X Angus and(or) Tarentaise genotypes were used.
Cows were
stratified within five supplement groups: soybean meal (SEM), bloodmeal
(BM), c o m gluten meal ( C m ) , animal fat (FAT) and range forage only
(CON).
SEM, CGM, EM, and FAT received 200 g/d rumen degradable
protein. EM and OGM received 200 g/d additional bypass protein and FAT
received 50 g/d additional bypass energy. Two groups of ten cows wore
fecal bags for a week in January and February.
Rectal grab samples
were obtained from all 61 cows concurrently with total fecal
collections.
Four groups of four cows wore vibracorders to estimate
daily grazing time in three intervals: 0701-1300, 1301-1900 and 19010700 and pedometers to estimate distance travelled per day. There were
no differences (Pc. 05) in forage organic matter intake (OMI), daily
grazing times (DGT), grazing time per interval (DGTI) or distance
travelled per day (DT).
Supplemented cows lost less weight and
condition
(P<.05,-14.5 kg,
-.68) than CON
(-44.4
kg,
-.95),
respectively.
CMI and DGT were expressed within a narrow potential
range under low forage quality and mild environmental conditions.
In
1987, 16 cows of the same genotype as trial I wore vibracorders and
pedometers using the same methods as trial I. Four groups of four cows
wore fecal bags for 96 h collections within a week in January and
February. Rectal grab samples were obtained daily from all cows. All
cows were bolused daily with 10 g chromic oxide. Acclimation lengths
were determined for daily CMI, DGT, and DGTI under short-term thermal
stress (STTS) and wind-chill temperature (WCT). Acclimation lengths of
I to 3 days increased (MI (Pc.05) and decreased DGT (Pc.05) to both
STTS and WCT. DGTI showed variable responses. Generally, larger DGTI
responses were associated with longer acclimation lengths.
Cows
returned to normal CMI and DGT regimes within 72 h.
The presence of
fecal bags decreased DGT by 24.2 minutes (Pc.001). Grazing times from
1301-0700 were unaffected (R>.05).
From 0701-1300 grazing times were
decreased 10.7 minutes (Pc.001) by presence of fecal bags due to bags
being full before being changed prior to 1130 h.
Adjustment factors
should be made for animals wearing fecal bags until a more suitable
method for free-roaming conditions becomes available.
I
INTROEUCnON
Available winter
grazing livestock.
forage seldom meets
nutrient
requirements
of
Consumption of available protein and energy by
prepartum cows grazing winter range is usually below National Research
Council . (1984)
recommendations
reproduction can be
impaired
by
such
magnitude
(Allison 1985,
that
subsequent
Cordova et al.
1978).
Supplementation has been used to moderate forage nutrient deficiencies;
however,
responses vary with both the year and type of supplement
(Kartchner 1981) and with timing of supplemental feeding (Adams 1985).
Also, Vhen compared to the relatively small cost of grazed forage it is
often expensive.
Russell et al.
(1979)
stated the
largest single
economic cost in the production of a weaned calf is that of feeding the
cow during the winter.
winter
forage
and
If prepartum cows can efficiently utilize
maintain
acceptable
production
levels
without
supplementation, it would significantly reduce or even eliminate this
cost.
In addition to the constraints' of low quality forage, grazing
livestock must adapt to an energetically demanding environment.
.Fluctuations in winter environmental conditions cause metabolic
and
behavioral
(1985)
stated
responses
these
for maintenance of homeothermy.
responses
vary
with
the
temperature
environment relative to the lower critical temperature
animal and the duration of cold exposure.
with hormonal
and metabolic
functional
consequence of prolonged cold or heat
Kennedy
of
the
(LCT) of the
Acclimation is associated
changes
that develops as a
exposure and,
therefore,
is
2
associated with seasonal changes in the thermal environment than with
daily or short-term weather fluctuations (NRC, 1981).
Once animals are
acclimated to winter environmental regimes, energy expenditures remain
relatively constant.
To maintain energetic efficiency under these conditions,
free-
roaming prepartum cows' adapt winter foraging strategies to satisfy
energy demands.
These strategies have been difficult to assess because
winter environmental conditions often prohibit intensive studies with
grazing livestock.
Consequently, range forage intake values for the
winter months are rare and continuous measurements are nonexistent.
Identifying range forage intake responses to the winter environment
would provide
producers
to
insight into critical nutritional periods and enable
conform management
strategies to those periods; thus
optimizing animal efficiency and economic returns.
Considering these
restraints, our objectives were:
(1)
to
determine
range
forage
intake
and
grazing
behavior
responses of prepartum beef cows to supplementation and the
winter environment and,
(2) to quantify acclimation lengths for range forage organic
matter intake and daily grazing times of free-ranging pregnant
beef cows under short-term thermal and wind-chill stresses.
3
IiITERATURE REVIEW
Introduction
During the winter, forage available for grazing is bulky., fibrous
and has a relatively low digestible energy content.
usually deficient in' protein,
1950,
Marsh et al.
1959).
In addition, it is
phosphorus and carotene
(Cook et al.
Protein is generally the most limiting
nutrient in winter forage, with typical values ranging from 2.8 to 7.5
percent (Miner 1986, Adams et al. 1987).
These low protein levels may
inhibit rumen microflora activity and the rate of cellulose digestion.
Blaxter and Wilson (1963) and Elliot and Topps (1963) determined that
mature cattle and sheep consume less when the protein content is below
8 to 10 percent of the forage dry matter.
To compensate for these
deficiencies, forage intake must increase to satisfy nutrient demands.
However, the high fiber, low energy conditions of winter forage often
limit
intake
disappearance
by
reticulo-rumen
from that organ
volume
(gut
fill),
(Campling and Balch
Forbes 1974, Ellis 1978, Grovum 1979).
and
1961,
rate
of
Baile and
Although energy demands may be
met if winter forage is consumed in large enough quantities (Cook and
Harris 1968,
Clanton 1981)
the physical constraints imposed by the
forage and reticulo-rumen volume usually inhibit this increase.
addition
ruminants
to
the
must
constraints
adapt
of
foraging
a
low
quality
strategies
conditions to maintain energetic efficiency.
to
diet;
winter
In
free-roaming
environmental
4
The
climatic
environment
acts
on
animals
to
influence
thermoregulation as well as affecting the availability and quality of
nutrient supply (Thompson 1973, Robertshaw 1974).
that
environmental
stress,
including
energy
Osuji (1974) stated
costs
of
grazing
and
walking, may raise the maintenance requirement 25 to 50% above that of
indoor animals.
and Malechek
Comparisons
Other studies.
Young and Corbett (1972) and Havstad
(1982), believed this increase ranged from 40 to 70%.
between
studies
examining
environmental
influences
on
winter foraging strategies are often difficult to interpret because of
variations in acclimation states and thermoneutral zones of the animals
utilized.
For
example,
Adams
et
al.
(1986)
proposed
a
positive
correlation existed between daily grazing time and range forage intake
as winter ambient air temperatures decreased.
In contrast, Dunn (1986)
reported daily grazing time for any day was unrelated to previous daily
grazing time and previous daily temperatures, which ranged from 8 C to
-25 C.
Currently,
winter
environment
there are few studies addressing affects of the
on
foraging
strategies
and
acclimation to winter environmental variables.
the
time
course
of
Understanding range
forage intake and grazing behavior responses to winter environmental
conditions and low quality forage provides insight into the mechanisms
involved in acclimation and may delineate critical nutritional periods
during the winter.
This review will discuss effects of the winter environment on heat
production and metabolism,
foraging strategies,
digestive responses;
and
pregnancy
on
supplementation
and
effects
strategies, body weight and body condition.
winter
foraging
5
Heat Production and Metabolism
The
thermal
consequence
of
state of an animal
its
prior
thermal
at
any
instant in time
exposure,
rate
of
is a
thermogenic
metabolic responses, and the net rate of physical heat exchange with
the environment (Young 1976).
Two key concepts in understanding the
relationship between
animals and their thermal environment are the
thermoneutral
zone
(TNZ)
and
Young
Christopherson
environmental
energy
temperatures
expenditures
and
lower
(1981)
in
critical
defined
which
an
the
temperature
TNZ
as
a
animal, without
above -the maintenance
alter the rate of heat loss from the body.
requirement,
(LCT).
range
of
additional
can
readily
This balance between heat
loss and heat gain must be regulated to maintain homeothermy (Monteith
and Mount 1974, Robertshaw 1974).
The lower boundary of the TNZ is
called the lower critical temperature (ICT).
Young (1981) defined the
ICT as the temperature below which an animal must immediately increase
its rate of heat production to maintain homeothermy.
This increase in
heat production may take anywhere from 30 minutes to 3 hours to reach
equilibrium
(Joyce
and
Blaxter
1964,
Webster
and
Blaxter
1966)..
Specific ICT values for pregnant beef cows range from -11 to -23 C
(Webster 1970)
and are dependent on age, biological type,
lactation
state, level of nutrition, history of thermal acclimation, insulation,
and behavior (Webster 1970, Young 1975).
As temperatures drop below the ICT, animals experience acute or
short-term
thermal
stress
which
stimulate
specific
thermogenic
6
mechanisms for maintenance of homeotherrny.
These mechanisms include:
vasoconstriction at the skin surface, piloerection of the hair coat,
and postural changes
(Young 1976).
Christopherson and Young
(1986)
reported the extra heat generated by these mechanisms will be directly
proportional to the number of degrees the temperature has dropped below
the BZT.
Short-term behavioral responses compensate for increased loss
of
heat
body
homeotherrny.
to
the
environment
and
aid
in
the
maintenance
of
These mechanisms may balance homeotherrny in the short
term; however, if the duration of cold exposure persists for a longer
period of time animals must
achieve
thermal
physiologically
to
balance.
achieve
environmental conditions.
results
in
an
increase metabolic heat production to
increased
Cattle
an
adapt
acclimation
state
in
resting
metabolic
response
to
rate
associated
with
Young and Christopherson
reported an 8 to 40 percent rise in resting metabolic heat
production during chronic cold exposure.
Increases in heat production
are fueled by shivering or nonshivering thermogenesis
1979)
and
Chronic cold exposure (one week or longer)
increased resting metabolic heat production.
(1974)
morphologically
which are powered by free fatty acids
(Gonyou et al.
(Young 1975)
obtained
through oxidation of adipose tissue (Blaxter and Wainman 1961).
This
eventually leads to a higher summit metabolism which enables a downward
shift in the BZT and lowering of the TNZ.
these
adaptations
result
in
a
However, energetic costs of
persistently
higher
production which leads to increased feed requirements.
rate
of
heat
7
Winter Foraging Strategies
Many reviews on forage intake conclude that free-roaming ruminants
increase intake in response to cold exposure (Baile and Forbes 1974,
Weston 1979 1982, Arnold 1984).
from two basic sources:
This shift in intake apparently arises
(I) acute or short-term thermal stress (STTS)
that challenges hameothermy of susceptible animals and (2) metabolic
and digestive function changes arising from thermal acclimation (Young
1986).
for
IXiring STIS metabolic heat production increases to compensate
a
faster
compensates
intake.
rate
of
for this
heat
loss to
the
environment.
increased metabolic demand by
The
animal
increasing food
Senft and Ritterihouse (1985) reported if animals are exposed
to temperatures within their thermoneutral zone, feed intake should be
independent of environmental temperature.
drop
below
the
LCT,
animals
increase
However,
forage
if temperatures
intake
or
decrease
production levels due to a demand for increased heat production.
The
level of intake helps maintain homeothermy through increases in the
heat of fermentation.
metabolic
rates
The level of intake also influences the LOT.
increase
during
SITS,
increased
increased heat production and the LCT decreases.
Mount
(1979)
temperatures
and Ames and Ray
intake
increased
(1983)
intake allows
As
for
This agrees with
who stated at extremely cold
to meet thermoregulatory needs.
In
contrast to this, Senft and Rittenhouse (1985) and Malechek and Smith
(1976)
reported
intake
decreased
in response to daily
changes from an acclimation temperature.
temperature
Also, Dunn (1986) reported
8
short term decreases in daily grazing times in response to either rapid
decreases
or
increases
in daily
ambient
air
temperatures.
The
discrepancies between these studies probably relate to the acclimation
state of the animals, the influence of other environmental variables on
foraging strategies,
year
and when the studies were conducted during the
(late fall or early winter versus mid to late winter).
Once
acclimated to cold, cattle show a 30-40% elevation in resting metabolic
rate (Young 1975, Christopherson 1985) which is independent of level of
feeding but linked to increased thyroid hormone activity (Westra and
Christopherson 1976,
energy
demand,
Christopherson 1985).
along
with
elevated
This increased metabolic
thyroid
levels,
potentially
increases appetite drive and may allow for increased intakes.
the effects of chronic cold exposure are significant,
Although
they are not
always encountered and behavioral acclimation becomes a more important
adaptive mechanism (Rittenhouse and Senft 1982).
Physiological acclimation must occur if animals are to survive.
However,
because
of
natural
day-to-day
fluctuations
in
climatic
variables an animal's physiological state is unlikely to be in exact
synchrony with the environment.
Behavior compensates for discrepancies
between physiological state and current environmental conditions by two
mechanisms:
decreased activity and movement to favorable microclimates
(Senft and Rittenhouse 1985).
These mechanisms, which also include
decreased respiratory rate and water intake (Young 1975, Gonyou et al.
1979),
allow
for
a
fine-tuning
of
thermoregulatory
responses.
Generally, to reduce these energetic demands ruminants must either move
9
to more favorable microenvironments or repartition metabolizable energy
for thermoregulation.
Senft and Rittenhouse (1985) hypothesized in a constantly changing
environment, short-term behavioral responses are critical to the energy
balance
of
domestic
animals.
They
suggested
cattle
were
physiologically acclimating to the mean temperature regime experienced,
over the previous 11 days.
This study was conducted for twelve months
and may be an accurate time frame for an entire year; however, during
the winter months animals seem to respond only to temperatures regimes
experienced from the previous one or two days (Dunn et al. 1988).
This
short-term response occurs unless the duration of cold exposure induces
a new acclimation state.
Several other climatic variables influence foraging strategies and
acclimation states.
Wind aggravates the effects of temperature.
At
cold temperatures, wind induces higher heat production (Webster 1970)
and a higher metabolic rate (Christopherson et al. 1979).
Adams (1984)
reported decreased grazing times as wind velocity increased.
Axnes
(1974) and Ames and Insley (1975) determined wind velocities under 32
km/h removed an insulating layer of air surrounding the animal, but air
still remained trapped in the hair coat.
Above 32 knyTt this insulating
layer of air was destroyed which accelerated the rate of heat loss to
the environment.
In addition to wind, barometric pressure influences
foraging strategies.
Senft and Rittenhouse
(1985)
reported low to
intermediate rates of change in barometric pressure resulted in a rapid
increase in grazing time, while higher rates of change led to a gradual
decline in grazing time.
Malechek and Smith (1976) also reported an
10
increase in grazing time in response to absolute pressure changes.
Relative humidity may also affect grazing activities but this occurs
mainly in warm or tropical climates (Arnold and Dudzinski 1978).
Very
little is reported on the effects of solar radiation on winter foraging
strategies;
however,
it
may
be
very
important
in
maintaining
homeothemy. , Cattle may gain heat from long and short wave radiation
which
the
would minimize heat transfer to the environment.
above
findings.
Low et
al.
(1981)
stated very
In contrast to
little of the
seasonal changes in grazing behavior may be explained by variations in
temperature, rainfall, solar radiation or wind.
could be affected by these factors.
Timing of activities
LXmn (1986) reported total daily
grazing times of 9.0 hours per day even though individual daily grazing
periods declined in response to rapid fluctuations in daily ambient air
temperatures.
Rittenhouse and Senft
regulate
grazing
time
(1982) suggested the ability of cattle to
in
response
to
changes
in
environmental
conditions is an evolutionary adaptive mechanism which allows animals
to respond to a wide variety of environments; however, the mode of
action or consequences of adaptive change are not clear.
Several
hormones have been implicated in assisting the acclimation process
including
catecholamines
(epinephrine
and
norepinephrine),
glucocorticoids, thyroids (thyroxine and triiodothyronine), insulin and
others.
The activity and interrelationship of hormones during cold
exposure
and
physiological
acclimation
are
complex
and
not
well
understood but they seem to influence digestive responses more than the
acclimation process itself (Heroux 1969, Thompson 1973, Johnson 1976,
11
Christopherson et al. 1978).
thermal
strain,
mechanisms
conditions encountered.'
Although behavioral acclimation offsets
involved may not
compensate enough
for
To further aid in thermal balance, digestive
functions also change in relation to cold exposure.
Digestive Responses
The winter environment has some striking influences on digestive
function for free-roaming prepartum cows.
related
to
duration
of
cold
exposure
Most of these responses are
and
whether
an
animal
is
acclimated to winter environmental conditions.
During cold exposure
reduced.
Westra
and
(either acute or chronic) digestibility is
Christopherson
(1976)
showed
dry
matter
digestibility depressed by 0.2 units per degree C drop in temperature.
Shnilar results were obtained by Christopherson (1976), Kennedy et al.
(1976) ,
Kennedy
and
Milligan
(1978)
and
Kennedy
et
al.
(1982).
Although digestibility is reduced, passage rate of digesta (mainly in
the
reticulo-rumen)
is
Kennedy et al. 1986).
increased
(Westra
and
Christopherson
1976,
This increase occurs within hours of the onset
of cold exposure and persists for the duration of the exposure.
Faster
passage rates allow ruminants to increase intake and compensate for the
bulk limiting.affects of available winter forage; which in turn may
allow
animals
to
maintain
production
levels.
The
effects, of
temperature on digestibility occur mainly on forage-based diets and not
when concentrate diets are fed (Kennedy et al. 1982).
However, there
12
is
evidence
that
digestibility
of
different
forage
diets
may
be
influenced to different extents (Kennedy 1985).
Another
consequence
contraction rates.
of
cold
exposure
are
higher
reticular
During both short-term and chronic cold stress,
increased rates of reticular contractions were reported for cattle and
sheep
1985).
(Westra and Christopherson 1976,
Gonyou et al.
1979, .Kennedy
Increased contraction rates may not simply be a consequence of
increased passage rates.
Deswysen and Ehrlien (1981) stated there may
also be a change in the rate of movement of particles from the rumen to
the reticulum.
selective
Geisecke et al.
for particulate
(1975)
passage
hypothesized the omasum is
rate and
selection of particles
through the reticulo-omasal orifice may limit particle passage to the
reticulum.
This in turn may lead to increased contraction rates.
Increase! passage rates are also associated with decreased rumen
retention time
(Warren et al.
(Kennedy et al. 1976).
1974) and shorter rumen turnover time
The reduction in retention time significantly
alters the amount of cell wall constituents (CWC) and organic matter
(CM) degraded.
for
Kennedy et al. (1976) reported apparent digestion of CM
pelleted. brome
grass
in
the
rumen
of
sheep
was
30%
in
a
thermoneutral environment (20 C) but only 24.2% during cold exposure (0
C).
This decrease in digestibility was also negatively correlated
with rumen turnover time.
However, the quantity, of microbial nitrogen
synthesized in the rumen did not
alter significantly,
improved efficiency of rumen microbes.
which shows
This agrees with Kennedy and
Milligan (1978) who reported efficiency of microbial protein synthesis
in the rumen and nitrogen recycling were enhanced during cold exposure.
13
Because digestion
examined
the
exposure
did
in the reticulo-rumen is reduced,
possibility
not
gastrointestinal
of
increase
tract;
increased
intestinal
digestibility
however,
volatile
proportion to the reduction of CM digested.
of
Kennedy
(1985)
digestion.
Cold
CWC
fatty
or
acids
CM
in
changed
the
in
Specifically, there was a
decrease in acetic acid and increase in propionic acid which agrees
with similar work conducted by Kennedy et al.
Milligan (1978).
(1976) and Kennedy and
This ,change probably occurred because rumen microbes
were less dependent on CWC as an energy source.
Although total organic matter digestion is reduced during cold
exposure,
faster clearance from the reticulo-rumen causes increased
protein flow to the gastrointestinal tract; which increases appetite
and facilitates increases in intake (Egan 1977).
Kennedy (1985) also
reported an increase in the flow of non-ammonia nitrogen to the small
intestine during cold exposure.
increased
dietary
flow
of
protein
digesta
escaping
from
These increases may arise from either
the
reticulo-rumen
fermentation),
increased
(and thus more
efficiency
of
microbial protein synthesis in the rumen (Kennedy and Milligan 1978,
Kennedy et al. 1982) or increased flow of pancreatic secretions (Kato
and Young 1984).
of the animal.
Digestive changes help maintain the nitrogen balance
The net result is an increase in total food requirement
to compensate for reduced energy digestibility; which may account for
some of the increased forage intake values during cold exposure.
These
changes in nitrogen transactions may allow ruminants to utilize diets
with lower nitrogen content which could compensate for the nutrient
deficiencies of winter forage (Christopherson and Young 1986).
14
Digestive responses aid in countering the effects of fluctuating
environmental conditions and nutrient deficiencies; however, intake of
winter forage may still not satisfy nutrient demands.
provides
additional
nutrients
in
an
attempt
to
Supplementation
offset
these
deficiencies.
Supplementation
Reproductive performance of the beef cow is closely aligned with
■
I
nutritional status (Wiltbank et al. 1962, Dunn et al. 1969, Clanton and
Zimmermann
1970,
Bellows
and
Short
1978,
Bellows
et
al.
1982).
Consumption of available protein and energy by prepartum cows grazing
winter, range
magnitude
is
that
usually
below NRC
subsequent
Cordova et al. 1978).
(1984)
reproduction
is
recommendations by
impaired
(Allison
such
1985,
Supplementation is used to preclude lengthened
postpartum interval and moderate forage nutrient deficiencies but is
expensive when compared to the cost of grazed forage (Russel et al.
1979).
Tiimiting this cost, while maintaining reproductive performance
of the cow herd, would be of considerable economic importance to the
producer.
For
a
supplement
to
be
digestion by rumen microbes.
effective
it must
complement
forage
In addition, it should supply specific
nutrients deficient in available forage.
During the winter months,
these are generally protein and energy.
Meeting specific nutrient
requirements is often difficult because energy needs are met first and
protein will be used for energy until it is no longer limiting (Clanton
15
1981).
In addition to this, several studies have shown a substitution
effect of supplementation for available winter forage
(Holder 1962,
Raleigh and Wallace 1963, Rittenhouse et al. 1970, Bellows and Thomas
1976).
Although
microbial
received
protein
from
supplementation
synthesis
range
forage
and
alone
may
allow
increase
for
the
(Zinn and
optimization
digestible
Owens
of
protein
1981);
it
also
decreases digestibility of cellulose and gross energy (Cook and Harris
1968).
As stated before, during cold exposure efficiency of microbial
protein synthesis either remains unchanged
increases (Kennedy and Milligan 1978).
is
available,
supplementation
may
(Kennedy et al.
1976) or
If this is the case and forage
not
be
necessary
or
feasible.
Raleigh and Wallace (1963) and Kartdhner (1981) stated supplementation
during the winter when forage availability is not limiting and weather
conditions
are
mild
is
questionable.
Also,
Ames
(1986)
stated
deposition of fat during periods of abundant feed to be catabolized
during periods of feed shortage may be a sound management technique,
but may be less energetically efficient than using forage alone as an
energy source.
In addition, it renders animals less tolerant to cold
by decreasing external
insulation which
is
an
important factor in
minimizing SITS.
Supplementation affects
forage intake in various ways.
It is
generally accepted that high energy supplements derived from grain
sources depress voluntary intake while supplements high in natural
protein enhance intake.
type of supplement
However, responses vary with both the year and
(Kartdhner 1981) and with timing of supplemental
feeding (Adams 1985).
Other factors which may
contribute to these
16
differences include cow body condition entering the winter and forage
quality
variations.
Several
studies
have
shown
that
supplementation increases intake of a low protein feed
protein
(Clanton and
Zimnrermann 1965, Topps 1972, Clanton 1981, Branine and Galyean 1985).
Turrrer (1985) and Dunn (1986), using the same study site as the present
stud/, reported increases in range forage intake in supplemented versus
unsupplemented pregnant cows. ,These increases seem to be dependent on
the crude protein concentration of the forage.
Generally,
protein
supplements increase intake when crude protein content of the forage is
below
8%
(Allison
1985).
The
positive
effect
of
protein
supplementation on intake, and digestibility, may be due to a positive
effect on microbial digestion (Campling et al. 1962, Egan 1965).
recent studies
(Goetsch et al.
decreased microbial
positive
strong
efficiency.
and negative
evidence
1984)
shows
have shown both increased and
Although
intake responses
that
small
More
studies
to protein
amounts
of
increases intake when forage quality is low.
have
shown both
supplementation,
supplemented
protein
For more comprehensive
reviews of supplementation affects on forage intake, digestibility, and
rumen kinetics see Siebert and Hunter (1981), Allison (1985) and Miner
(1986).
Supplementation
also
affects
grazing
behavior.
Adams
(1986)
determined forage intake for unsupplemented steers was greater than
steers supplemented in either the morning or afternoon.
This was
supposedly caused by disruption of normal grazing activity.
During the
winter animals often became accustomed to supplementation at specific
times.
If this corresponds with intensive grazing periods, producers
17
are minimizing the value of their forage and increasing the costs of
supplementation by limiting intake of that forage.
Cattle normally
graze during the daylight hours, which are relatively short during the
winter months.
variable
and
Although nighttime grazing does occur, it is extremely
more
of
an
individual
animal
characteristic.
For
supplementation to be effective it should compliment grazing times
rather than disrupt them.
Although supplementation can reduce weight loss,
pregnant beef
cows may loose substantial amounts of weight during winter feeding and
recover satisfactorily the next spring by compensatory gains (Furr and
Nelson 1964, Jordan et al.
1979).
1968,
Lusby et al.
1976,
Russel et al.
This may or may not affect calf birth weight.
Hironaka and
Peters (1969) reported cows wintered on low nutritional levels produced
calves of the same birth weight as those wintered on high nutritional
levels.
Jones et al.
(1979) reported an average weight loss of 60 kg
during the winter for Hereford cows which significantly reduced calf
birth weights although it had no effect on either pre-weaning daily
gain or weaning weight of the calves.
Thus,
it appears the energy
demand of the fetus was met before the demand to maintain body tissues
of the dam; even to the point where body tissue was lost.
This agrees
with Robinson and Forbes (1967) who stated the fetus has priority for
amino
acids
during
supplementation
nutrition.
nutrition
is
conditions
dependent
upon
of
undemutrit ion.
body
condition
and
Pre-calving
post-calving
Poor pre-calving nutrition may be tolerated if post-calving
is excellent.
Producers must
take into account several
factors when determining the feasibility of supplementation.
Some of
18
these
factors
include
the
quantity
and
nutritive
value of
forage
available for grazing, environmental conditions encountered that either
allow or restrict grazing, and economic feasibility of supplementation
(Raleigh and Wallace 1963 , Kartchner 1981).
An important component of an animal's performance is it's stage of
production.
During the winter,
a majority of cows in the Northern
Great Plains are pregnant and this has pronounced effects on forage
intake and grazing behavior.
Pregnancy
During the latter part of pregnancy, cows have decreased forage
intake due to increased fetal growth and limitei abdominal capacity
(Campling and Murdoch 1966,
Curran et al.
Forbes 1969, Putnam and Bond 1971).
significant correlation between the
1967,
Owen et al.
Leinkert et al.
1968,
(1966) showed a
intake decline in the last six
weeks before parturition and calf birth weight.
One explanation for
decreased intake is the compression of the rumen by the growing uterus.
Bines (1971) stated that capacity of the abdominal cavity appears to be
limited by
pregnancy,
although
the extent
roughage
the
to which the
rumen can stretch.
In early
intake may be maintained or even increase even
abdomen becomes more distended.
Eventually,
further
distention is impossible and fetal enlargement within the abdominal
cavity occurs at the expense of rumen capacity; thereby reducing food
intake
(Forbes
1969).
However,
the
animal
is
apparently able to
increase passage rate as pregnancy advances, thus offsetting some of
19
the intake declines due to pregnancy (Graham and Williams 1962, Forbes
1970) .
Physical competition for space may not be the only reason for
decreased intake.
Forbes
(1970) stated, decline in intake is due to
increased estrogen secretion in the last few weeks of pregnancy.
logical reasons include preoccupation with birth,
Other
seeking a suitable
place for parturition, and discomfort which may disrupt normal winter
foraging strategies.
An important and often undervalued factor determining the ability
of cows to
overwinter
is body condition.
When
in high condition
entering the winter, more body reserves may be used to compensate for
increased energy demand from the growing fetus and thermal environment.
However, when in low condition entering the winter, there are fewer
body reserves and therefore; ,an even greater demand on the body, with
drains from both the growing fetus and the thermal environment.
et al.
small
Ward
(1987) compared body weight and condition changes of large and
frame pregnant cows
in either fat or thin condition.
They
determined that small frame, thin condition cows lost less body weight
than large frame, fat cows; possibly due to lower initial body weights.
Hcwever, all groups of cows lost approximately the same amount of body
condition.
Whitman
Body condition also influences reproductive capability.
(1975)
reported
for cows
in good,
moderate
and thin body
condition at calving, their chance of estrus at 60 days was 0.91, 0.61
and
0.46,
respectively.
Thus,
it
maintain cows in good body condition
scale)
entering
the
winter
to
appears
that
producers
should
(approximately 5 on a I to 10
enhance
postpartum
reproductive
20
capability
and
facilitate
adaptations
conditions.
<!
to
winter
environmental
21
MATERIALS AND METHODS
Study Site
During the winters of 1986 and 1987, two trials were conducted at
the Red Bluff Research Ranch, Norris, Montana, in cooperation with the
Montana
Agricultural
Experiment
Station.
Trial
December 15, 1985 and concluded March 6, 1986.
15, 1986 and ended February 28, 1987.
I
was
initiated
Trial 2 began December
Both trials were conducted on a
324 ha pasture with long north-facing slopes and areas of steep slopes
and rocky outcrops. The pasture lies within section 18, T. 3S., R. IE.
'
Elevation ranged from 1400 to 1900 m with annual precipitation
averaging 350 to 406 mm (Ross and Hunter 1976).
An important feature
of the pasture was the dominant southwesterly wind that kept forage
accessible throughout both trials.
Estimated carrying capacity was 1.2
ha per animal unit month (Ross and Hunter 1976).
The
pasture
was
a
silty
range
site
in
good
condition
with
vegetation composed of 65% grasses and 35% forbs and woody species
(Ross and Hunter 1976).
fAqroovron
fFestuca
sites
Dominant grasses include bluebunch wheatgrass
spicatum), needleandthread
(Stipa
idahoensis) and basin wildrye
surrounding
rocky
oonderosa), limber pine
(Juniperus scopulorum).
outcrops
Turner
(Elvmus cinereus).
contained
CPinus flexilus)
(1985)
species found at Red Bluff Research Ranch.
comata), Idaho
ponderosa
pine
fescue
Shallow
(Pirns
and Rocky Mountain juniper
provides a complete list of
22
Animals
Trial
I utilized 61 pregnant cows
(3- to 6-yrs-old)
randomly
selected from the Red Bluff Ranch herd based on expected calving dates
on or near March 15.
Trial 2 utilized 16 pregnant cows selected from
the ranch herd based on body weight (525-575 kg) and age (5-yrs-old).
All cows were artificially inseminated to Angus bulls with expected
calving
dates
approximately
March
15.
Genotypes
combinations of Angus X Hereford and(or) Tarentaise.
weight and condition score
were
various
Initial mean body
(1= thinnest to 10= fattest)
(LaMontagne
1981) were 520 kg and 4.5 for trial I, and 550 kg and 4.1 for trial 2,
respectively.
For 6 months preceding initiation of either trial, cows
grazed native range and had no access to supplement.
Treatments
Prior to the initiation of trial I, cows were randomly allotted
within age to five supplement groups:
(BM), c o m
gluten meal
( C m ) , animal
soybean meal
fat
(SBM), bloodmeal
(FAT), and control
which received range forage only (Miner 1986).
(GON),
Composition of each
supplement is listed in Table I.
All supplements contained 200 g/d
rumen
satisfied
degradable
protein.
This
criteria
specified
by
Petersen and Clanton (1981), who stated ruminal protein needs must be
met before a response of protein presented to the small intestine might
be seen.
SBM was formulated to meet ruminal protein needs only.
EM
23
Table I.
Supplement composition^ (g/d), Trial I.
Supplement
Protein Availability
Bypass(g) Rumen(g)
g fed
g.CP
g TDN
SBM
570
250
430
50
200
EM
SBM
230
450
Total 680
200
200
400
340
40
480
160
40
200
40
160
200
CGM
SBM
Urea
450
140
16
Total 606
290
60
50
400
370
100
0
470
190
10
0
200
100
50
50
200
FAT
SBM
210
570
Total 780
0
250
250
410
430
840
0
50
50
0
200
200
CON
_
_
_
—
—
aEach supplement group also contained 50 g dried molasses and
4.5 g Molasses Booster (Feed Flavours, Inc.)
and
GGM were
sources
source, respectively.
of bypass protein
from an
animal
and plant
FAT, a bypass energy source, was provided to if
any observed response was due to bypass protein or bypass energy.
Further rationale for these supplement formations and their subsequent
metabolic uses is presented in Miner (1986).
Supplements also included
35 g/d chromic oxide premix (25% Cr2O3 and 75% ground c om) used as an
external
marker
for
(Raleigh et al. 1980).
determination
of
fecal
organic
matter
output
Supplements were fed individually on alternate
days at approximately 1130 h.
Throughout
supplementation.
trial
2
all
cows
grazed
native
range
without
This methodology was implemented to provide baseline
'24
data for winter grazing behavior and winter range forage intake without
the confounding affects of supplementation.
At the initiation of both trials, all cows were injected intra­
muscularly with 20,000,000 IU Vitamin A.
In addition, all cows had
access
containing
to
a
loose
iodized
salt
mixture
30%
dicalcium
phosphate and 30% potassium chloride.
Measurements
Grazing Behavior
In
trial
I,
four
cows
from
each
supplement
(n=20)
wore
vibracorders (Stobbs 1970) to estimate daily grazing time (DGT).
day was divided into three grazing intervals:
1901-0700.
Each
0701-1300, 1301-1900 and
These intervals were chosen to represent morning, afternoon
and nighttime grazing periods.
(n=16)
wore
vibracorders to estimate DGT for the same intervals as trial I.
Both
years,
animals
wore
the
same
In trial 2,
vibracorder
all cows
throughout
Vibracorder charts were changed weekly at 1130 h.
trial.
Charts were read as
hours grazed per interval (DGTI), rounded to 15 minutes.
the sum of DGIT for each interval for each day.
the
Total DGT was
No other activity
levels were assigned.
Distance travelled per day
(Anderson and Urquhart 1986).
(DT) was estimated using pedometers
During both trials pedometers were worn
on the front left foot and rezeroed every week (trial I n=20, trial 2
n=16).
Calibration was accomplished by zeroing the pedometers with
25
cows in the chute,
then moving the cows for approximately one mile
while following them with a calibration wheel.
The wheel was 2 m in
circumference and recorded the number of wheel revolutions.
After
returning the cows to the chute, pedometers were removed, reread, then
compared to the actual readings from the calibration wheel.
This
procedure was repeated twice during trial I and four times during trial
2, with an average adjustment factor applied to each pedometer reading
for each cow.
Fecal Organic Matter Output
In both trials,
fecal organic matter output
(PO) was estimated
using total fecal collections and a Cr2O3 dilution technique (Raleigh
et al. 1980).
Total fecal collections for trial I were made on two
groups of ten cows
(four per supplement, n=20) using fecal bags and
feces/urine separator flaps
(Kartchner and Rittenhouse 1979).
Each
group wore bags for seven total days in January and February.
Bags
were charged daily at 1130 h.
were collected
from all
Rectal grab samples for Cr2O3 analysis
61 cows
at the
same time as total, fecal
collections.
Durirg trial 2, total fecal collections were obtained from four
groups of four cows
Collections
(96 h)
(n=16)
using the same methodology as trial I.
were obtained from each group within a week in
January and a week in February.
h.
Samples were collected daily at 1130
Rectal grab samples were obtained daily at 1130 h from all cows for
26
Cr2O 3 analysis.
In addition,
all cows were bolused daily with 10 g
Cr2O3 in a gelatin capsule (size #10)..
For
mixed,
both
trials,
sampled
frozen.
and
collected
frozen. .
total
Rectal
fecal material
grab
was
samples were
weighed,
immediately
After thawing, dry matter and organic matter were determined
for each fecal sample following AOAC (1980) procedures.
The remainder
of the sample was dried at 100 C for three days then ground through a 2
mm screen using a Wiley mill.
Cr2O3 concentration for each sample was
determined through flame spectrophotometry using a method derived from
Fenton and Fenton (1979) and Costigan and Ellis (1986).
this
method
is
presented
in Appendix
Table
12.
An outline of
FO
per day was
estimated from rectal grab samples based on the following eguation:
F0/d=
[(g Cr2O3 fed per day)/(Cr2O3 (%)
in dry fecal sample) ].
adjustments were made to this original value.
recovery
For trial
g
Two
I, Cr2O3
per supplement was calculated and the quantity of Cr2O3 fed
per day was adjusted accordingly.
supplement
group
using
PO
Values were also adjusted for each
estimates
from
(Rittenhouse 1969, Rittenhouse et al. 1970).
total
fecal
collections
For trial 2, rectal grab
samples were adjusted individually for each cow based on PO from total
fecal collections.
\
Dietary Digestibility
During trial
three
I,
samples of grazed forage were collected using
esophageal-fistulated
cows
(VanDyne
and
Torrell
1964).
Collections were obtained periodically throughout the trial (Appendix
27
Table 14).
with
Samples of grazed forage for trial 2 were collected weekly
four rumen-fistulated cows using a total evacuation technique
(Iesperance et al. 1960).
or water.
The
Animals were penned overnight without feed
next morning,
rumen
cannulas
were
removed,
rumen
contents were emptied manually and rumen fluid was removed with a soup
ladle.
Contents were then stored in plastic tubs with lids maintained
at 37-39 C.
The inside of the rumen was washed down with water and
excess removed with a ladle.
Animals were allowed to graze freely with
other research animals for I to I 1/2 h.
cannulas
were
removed
subsampled and frozen.
rumen
and
cows
were
and
rumen
Animals were then gathered,
contents
were
removed,
mixed,
Initial rumen contents were returned to the
released.
All
cows
used
for
digestibility
estimates grazed concurrently with other research animals.
For both
trials,
In vitro
extrusa was frozen then freeze-dried and ground.
organic matter digestibility
(IVCMD)
of each sample was determined
using the B a m e s modification of the Tilley and Terry technique (Harris
1970).
For trial I, rumen inocula was obtained from two cows fed
mature grass hay ground through a tub grinder
(Appendix Table 14).
Rumen inocula for trial 2 was obtained from one cow used for total
rumen evacuations (Appendix Table 18).
In addition, during both trials
each extrusa sample was analyzed for crude protein content
1985).
(Galyean
28
Forage O m a n i c Matter Intake
Forage
organic
following equation:
matter
intake
(CMC), was
estimated
CMC= [daily FO (kg) / (I-IV(MD) ].
using
the
A complete listing
of the calculations used to estimate total CMC may be found in Table 2.
Table 2.
Estimation of fecal output (PO, kg) and forage
organic matter intake (CMC %BW, 0MB) from rectal
grab samples, Trials I and 2.
Item
Description
A
Optical density of CrgO^ in sample
B
Organic matter of sample
C
Weight of sample (all weighed to .25 g)
D
g Cr2O3 fed per day
E
g Cr2O3 per sample
DxE=F
BxCxF/A=G
H
GxH=I
J
(I/J)XlOO=K
L
I/1-L=M
(IVJ)XlOO=N
Adjusted Cr2O3 fed per day
kg fecal output per day
Adjustment factor per supplement
comparing recovery of Cr2O3 from total
collections with rectal grab samples
Adjusted fecal output
Body weight (kg)
Fecal output as % of body weight
Forage digestibility (IVCMD)
Total forage organic matter intake (kg/day)
Total forage organic matter intake (%BW,0MB)
29
Body WeicAit and Condition Score
During
both
years,
palpable
and
visual
condition
scores
(1=
thinnest to 10= fattest, LaMontagne 1981) were obtained separately by
two
technicians
at
the
beginning
and
end
of
the
trials.
Two
consecutive day body weights for trial I were measured at the beginning
and end of the trial after 12 h feed and water deprivation.
During
trial 2, all cows were weighed twice weekly. Calf sex, birth dates and
24 h calf weights were also recorded following each trial.
Climtic Conditions
During both trials ambient air temperature and wind speed were
measured
continuously
using
a
meteorograph
and
anemometer,
respectively.
Data Analyses,
Trial I. 1986
Data were analyzed using Statistical Analysis System's General
Linear Models Procedure (GIM)
(SAS 1985)
for
differences in winter
foraging strategies in relation to supplement.
Independent variables
in the model included OMI, DCT, DCTT, and DT.
Dependent variables were
individual
cow within
cow,
supplement,
and
individual
supplement.
30
Individual cow within supplement was utilized as the error term.
Calf
weights, and body weight and condition score change for each supplement
were analyzed using SAS GIM (1985).
weight,
and body weight and
Independent
variables
cow
included
supplement by cow interaction.
Dependent variables included calf
condition
supplement,
change per
individual
supplement.
cow
and
the
Individual cow by supplement was used
as the error term.
Trial 2. 1987
SAS GIM (1985) was utilized to determine the effect of previous
days ambient air temperature (lag(L) = I to 20 days) on daily OMI, DGT,
and DGTI.
This analysis utilized components of a model developed by
Senft and Rittenhouse (1985) to determine thermal acclimation lengths
for
cattle.
These
components
included
running mean
temperatures
(TaccIi (L))' daily mean temperature (Tjj , and short-term thermal stress
(SITS).
Running mean temperatures were calculated using mean daily
temperatures for the L days previous to the present day (i), but not
including day i:
Taccli(L)= [(sum of L days for j=l to L)*(T(i-j))]/L -
The variable L does not indicate the complete time for physiological
acclimation,
but time in the immediate past that has the greatest
impact on the current acclimation state.
chosen
to
approximate
values
of
9-14
L values of I to 20 days were
d
reported
by
Senft
and
Ritterihouse (1985) as the time course of thermal acclimation for cattle
throughout a year.
Tj. was calculated as the weighted mean of daily
maximum temperature (Imax(I)), daily minimum temperature CIkLn(i)), and
31
minimum
temperature
for
the
following
[(2^max(I) )+ (%Ln(i))+ (Tmin(i+l))]/4 -
day
(Txnin(i+1)):
Ti=
^TTS on day i was defined as
the difference between Tj and the hypothetical acclimated temperature
[TaccI (i)]:
STTS= [ (Ti)-(Taccl(i))]•
Responses of O H ,
to STTS for L values of I to 20 d were analyzed.
in the model were CMC, DGT and DGTI.
DGT and DGTI
Dependent variables
Indepenient variables included
individual cow, SITS, and individual cow by STTS. The model was tested
with individual cow by STTS as the error term.
the
effect
of
wind-chill
temperature
(WCT)
In addition to STTS,
on
CM,
DGT, and
for
acclimation lengths (L=I to 20 days) was analyzed using SAS GIM (1985).
WCT was calculated using an equation from Johnson et al. (1987) derived
from data published by Ames (1974) and Ames and Insley (1975).
The
equation incorporates linear terms for wind speed and temperature and, a
quadratic term for wind-speed squared:
(.995*temp) +
(.000013*wind)2].
and averaged per grazing
temperature value.
WCT= [(-1.4109)-(.00334*wind) +
Wind speed (km/d) was averaged daily
interval while
SITS was
utilized as
the
When combined with wind speed, STTS would give a
truer picture of acclimation lengths, because it represents deviations
from an acclimated temperature not just a daily average temperature.
Independent
variables
in
the
model
included
CM,
DGT, and
DGTI.
Dependent variables were WCT, individual cow, and WCT by individual
cow.
The error term was WCT by individual cow.
The influence of fecal
bags on DGT, DGTI, and DT was also determined using SAS GIM (1985).
Dependent variables were DGT, DGTT
and
DT.
included individual cow, week of the trial,
Independent variables
presence or absence of
32
fecal bags and the individual cow by fecal bag interaction.
was tested against individual cow by bag as the error term.
The model
33
RESULTS
Trial I. 1986
Forage Intake
,
There were no differences (P>.05) in forage organic matter intake
(%BW,
OMB)
between
supplements
supplements was 0.94 %BW.
0.95 BW, respectively.
3).
Average
CMI
for
all
BM and FAT had the highest OMI, 0.98 and
OGM, SBM, and 00N were lower and consistent,
ranging from 0.91 to 0.93 %BW.
trial.
(Table
IVCMD was estimated at 36% during the
CMI from rectal grab samples was adjusted based on percent
Cr203 recovery per supplement, amount of Cr203 fed per day, and fecal
Table 3.
Forage organic matter intake (0MI %BW, 0MB)
for each supplement,. Trial Ia*3.
Supplement
OMI+SE
(%BW, (MB)
00N
0.91+.05
SBM
0.92+.07
BM
0.98+.07
OtM
0.93+.06
FAT
0.95+.06
aIeast-squares means + standard error.
bR>.05.
34
output estimates
from total
fecal collections.
Estimates of fecal
outputs for all supplements are listed in Appendix Table 15.
Cr2Og recovery from rectal grab samples was 86.4%.
supplement ranged from 68.2 to 95.3%.
recovery per
supplement
from
rectal
Average
Mean recovery per
Cr203 fed per day and mean
grab
samples
and total
fecal
collections are listed in Appendix Table 13.
Grazing Behavior
Total
daily
grazing
times,
grazing
times
per
interval,
and
distance travelled per day (Table 4) were not different (P>.05) between
supplement groups.
The overall average DGT (0701-0700) was 8.56 h or
35.7% of each day.
CON cows had the highest DGT (9.04 h) followed by
SEM (8.75 h ) , CGM (8.39 h), FAT (8.33 h) and EM (8.26 h ) , respectively.
Overall average DGTI were 2.69 h from 0701-1300, 3.94 h from 1301-1900
and 2.24 h from 1901-0700.
18.7%
of
the
respectively.
hours
These times represented 44.8%, 65.7%, and
available
for
grazing
in
each
interval,
CON cows also grazed longer from 0701-1300 (2.79 h) and
1901-0700 (2.62 h ) .
OGM cows grazed the longest (4:11 h) from 1301-
1900; which represented the most important grazing interval for all
supplement groups.
Grazing times from 1901-0700 showed the greatest
variation among supplements while the 0701-1300 interval was the most
consistent.
4.6 tan/d.
Average distance travelled per day for all supplements was
SEM and CON walked the farthest,
respectively.
5.3 km/d and 5.1 W d ,
35
All supplement groups had one 3-, 4-, 5-, and 6-yr-old cow wearing
a vibracorder and a pedometer throuc^iout the study.
limitations and the study objectives,
Due to statistical
analysis combined age groups
within each supplement and did not analyze for age differences in OMI,
DGT or DGTI.
Table 4.
Daily grazing time (h), grazing time per interval (h)
and distance travelled (km/d) for each supplement.
Trial Ia .
Daily (h)
Supplement 0701-0700
Grazing Interval (h)
0701-1300 1301-1900 1901-0700
Distance
Travelled
(kny/d)
2.79b
3.SOb
2.62b
5. Ib
SEM
8.75b
2.61b
3.96b
2.29b
5.3b
EM
8.26b
2.67b
3.86b
1.94b
4.7b
4. Ilb
2.13b
4.Ib
3.88b
2.20b
4.Ob
.21
.31
2.68b
FAT
8.33b
2.69b
SEc
.19
S
OGM
CO
9.04b
%
n
CON
.58
aLeast-Squares means.
bPXOS.
cPooled standard error of the least-squared means
calf Rirtliweiaht. Cow Body Weight and Condition Score
Calf birthweight (Table 5) was unaffected (P>.05) by supplement.
Overall average calf birthweight was 38.4 kg.
Cow body weight (Table
5) was affected (Pc.OS) by supplement.
CON lost 46.4 kg which was more
(Pc.OS) than other supplement groups.
Cows in EM (-.46), CCM (-.69),
36
and FAT (-.63) lost less condition (P<.05; Table 5) than CON (-.95).
SBM lost .93 condition units which was different (PC.05) than all other
supplement groups.
Initial,
final,
and change in body weights and
condition scores for all supplement groups are listed in Appendix Table
16.
Table 5.
Calf birthweight (kg), pre-calving cow body weight
change (kg) and condition score change for each
supplement. Trial Ia .
Supplement
Calf
Birthweight
(kg)
i'
Body Weight
Change
(kg)
Condition
Score
Change
-
r
CON
37.8b
-38.Bb
-.95d
SBM
38.7b
-17.7C
-.93d
BM
38.4b
-4.5C
— .46e
CGM
39.2b
-10.8°
-.69e
FAT
38.Ob
-11.2°
-.63e
SEf
1.14
13.2
.122
aLeast-squares means.
bcd^Ieans without common superscripts differ (Pc.05).
fPooled standard error of the least-squares means.
Climatic Conditions
Average ambient air temperatures (C) for each month during trial I
are listei in Table 6.
On the average, temperatures were 1.3 C warmer
than long-term averages (National Oceanic and Atmospheric Association
1986).
These data show that weather conditions were relatively mild
37
during the trial and may have attributed to small differences in forage
intake and grazing times for supplemented and unsupplemented animal.
Table 6.
Average ambient air temperature (C), long-term
average, and deviation from normal for each month.
Trial I.
Deviation
From Normal
Temperature
(C)
Long-term
Average (C)
December
-1.5
-1.2
-0.3
January
-2.2
-3.4
+1.2
February
+1.3
-0.5
+1.8
March
+3.9
+1.3
+2.6
+0.4
2.8
-0.9
1.9
+1.3
1.2
Month
Mean
SE
Trial 2. 1987
Forage Intake
The effects of STTS (Senft and Rittenhouse 1985) on daily forage
organic matter intake for acclimation lengths of I to 20 days are
presented in Table 7.
STTS increased (MT (P<.05; .0003 to .0006 %BW)
for acclimation lengths of I, 2, and 3 days, but normal CMI regimes
returned within 72 h.
All other lag periods were not significant.
To
determine effects of wind speed on (MI, wind-chill temperature (Johnson
et al.
1987) was analyzed for acclimation lengths of I to 20 days
(Table 8).
WCT affected (ME similarly to STTS. Acclimation lengths of
38
I to 3 days increased CMI
(P<.05) by
acclimation lengths were significant.
Table 7.
.0002 to .0005 %BW.
No other
Again, normal CMI regimes
Significant responses of daily forage organic matter
intake (CHE %BW, 0MB) to short-term thermal stress and
magnitude of response (%BW) for acclimation lengths
of I to 20 days, Trial 2.
Acclimation
length
Period (d)
CHE/d
(%BW, (HE)
I
**
+.0003
2
**
+.0003
3
*
Magnitude of
Response (%BW)
+.0006 .
4-20
*P<.05
**P<.01
Table 8.
Significant responses of daily forage organic matter
intake (CHE %BW, (HB) to wind-chill temperature and
magnitude of response (%BW) for acclimation lengths
.. of I to 20 days, Trial 2.
Acclimation
length
Period (d)
CHE/d
(%BW, 0MB)
Magnitude of
Response (%BW)
i
I
*
+.0005
2
**
+.0002
3
.*
+.0003
4-20
*P<.05
* * P <.01
39
returned
within
72
h.
STIS
and WCT
influenced
acclimation lengths although responses were small.
CMI
for various
However, if these
adjustments do not occur over an entire winter then the additive
affects of decreases in CMI would impinge on survival.
These data
determine that animals are capable of making minute changes in CMI in
relation
to
acute
thermal
stresses
and
are
finely
attuned
with
environmental conditions.
In
vitro
organic
matter
digestibility
presented in Appendix Table 18.
from
rumen
extrusa
is
Chromic oxide recovery from total
fecal collections and rectal grab samples are found in Appendix Table
19.
Weekly fecal output estimates for all cows are listed in Appendix
Table 20.
:
f.
Grazino Behavior
The effects of STTS on total daily grazing times and grazing times
per interval for acclimation lengths of I to 20 days are listed in
Table 9.
DGT and CMI responded similarly to STTS. However, in contrast
to the positive effects of STTS and WCT on OMI; DGT decreased (P<.05) .
Acclimation lengths of I to 3 days were significant but responses were
gmal I (-.010 to -.005 h/d).
DGT was unaffected (P<.05) by all other
acclimation lengths (4 to 20 days).
unaffected (R>.05) by STTS.
Grazing times from 0701-1300 were
Grazing times from 1301-1900 and 1901-0700
showed several significant responses.
From 1301-1900 responses were
negative (.0007 to .005 h/d) for acclimation lengths of 8 to 20 days.
40
Generally, the more significant and larger responses were associated
with increased acclimation lengths.
positive and negative.
This
For 1901-0700 responses were both
interval probably represents the most
stressful period because there are no warming effects from sunshine.
The effects of WCT on DCT are listed in Table 10.
of I, 2, 3, and 14 days affected DCT (P<.05).
of STTS and WCT on CHE, and SITS on DCT.
small, ranging from .002 to .007 h/d.
Table 9.
Acclimation lengths
This follows the trends
Responses of DCT to WCT were
Grazing times from 0701-1300
Significant responses of daily grazing times (h) to
short-term thermal stress and magnitude of response
(h) for acclimation lengths of I to 20 days. Trial 2.
Acclimation
Length
Period (d) .
I
2 ,
3
4 ■
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
*P<.05
**P<.01
***P<.0bl
Grazing Intervals (h)
1301190107011900
0700
1300
Daily
0701-0700
* (-.010)
*** (-.003)
* (-.005)
•
* (-.0001)
*
**
**
■**
***
***
***
***
***
***
***
***
***
(-.0005)
(-.0006)
(-.0006)
(-.0006)
(-.0006)
(-.0006)
(-.0007)
(-.0007)
(-.0007)
(-.0006)
(-.006)
(-.007)
(-.005)
* (+.0002)
* (-.0008)
*
*
*
*
(+.0001)
(+.0003)
(+.001)
(+.001)
41
were unaffected (B>.05) by WCT for any lag day.
WCT for acclimation
lengths of I and 19 days affected (P<.05) grazing time from 1300-1901.
For lag day I, grazing time decreased .002 h/d while for lag day 19 it
increased .001 h/d.
Grazing times from 1901-0700 were affected by WCT
(P>.05) for acclimation lengths 3, and 8 to 20 days.
negative
(-.0007
to
-.011
h/d),
possibly
Each response was
showing
increased
influence during this nighttime grazing interval.
Table 10.
Significant responses of daily grazing times (h) to
wind-chill temperature and magnitude of response (h)
for acclimation lengths of I to 20 days, Trial 2.
Acclimation
Length
Period (d)
I
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Daily
0701-0700
* (-.007)
** (-.003)
* (-.005)
13011900
Grazing Intervals (h)
190107010700
1300
* (-.002)
* (-.005)
* (-.010)
* (+.001)
*P<.05
**P<.01
***Pk.001
*
*
**
**
**
***
***
**
**
**
**
**
***
(-.007)
(-.006)
(-.006)
(-.006)
(-.007)
(-.007)
(-.007)
(-.007)
(-.008)
(-.007)
(-.007)
(-.009)
(-.011)
wind
42
Influence of Fecal Baas on Daily Grazing Times
DGT decreased 24.2 minutes (4.8%) by the presence of fecal bags
(Pc.OOl, Table 11).
Grazing times from 1301-1900 and 1901-0700 were
unaffected (P>.05) by the presence of fecal bags.
Numerically, grazing
times were 35.7 minutes greater (28.1%) from 1301-1900 and 12 minutes
Table 11. Influence of fecal bags on daily grazing times (h)
and magnitude of response (min), Trial 2a .
Grazing Interval
Mean SquarefSE
P
Min
Daily (0701-0700)
8.49+1.29
***
-24.2
12.0
1301-1900
4.17+0.67
-
1901-0700
2.12+0.99
+35.7
0701-1300
2.40+0.73
***
-10.7
aIeast-squares means.
***P<.001
less (4.8%) from 1901-0700.
Presence of fecal bags decreased grazing
time (P<.001) from 0701-1300 by 10:7 minutes (7.4%).
This response was
dne to the weight of bags, prior to changing at 1130 h.
output
values
ranged
from
20
to
30
kg/d
per
Typical fecal
animal
and
visual
observations indicated that cows travelled and grazed less when bags
were full.
Distance
travelled per
Appendix Table 21.
day
in weekly
intervals
is
listed
in
43
DISCUSSION
Trial I. 1986
Forage Intake
There were no significant differences in forage organic matter
intake among supplement groups. ' Average C M
was 0.94 %BW, which was
consistent with values reported for free-roaming cows grazing winter
range.
Smith (1968), using similar methods as this trial, determined
intake at .96 %EW for cows grazing winter range in Nevada.
(1970)
reported
Nebraska.
intake
of
%BW
for cattle on winter range
in
Dunn (1986), using the same pasture and supplements, had an
average OMI of 1.25 %BW.
various ways.
intake.
1.0
Rittenhouse
EM,
Individual supplements influenced CMI
in
a bypass protein source, had the highest forage
Miner (1986) stated this may have been related to increased
fermentation rate and digestibility, or improved protein status caused
by increased protein presenter to the small intestine.
energy source, had the second highest OMI.
FAT, a bypass
Possibly, lipids from the
animal fat coated the soybean meal portion of this
supplement and
rymppd it to act like a bypass protein source in addition to a bypass
energy source (Miner 1986).
These results agree with Dunn (1986), who
reported similar CME responses for cows fed blood meal and animal fat.
Different
supplements
influence
CME
in
various
ways
among
years,
44
trials, and seasons (Kartchner 1981).
During the winter months, forage
quality estimates and environmental variables may limit differences in
forage intake to supplementation.
-
IVCMD of winter forage may range anywhere from 20 to 50%.
This
relatively high indigestibility is, hypothesized to limit intake through
rumen-fill mechanisms (Campling and Balch 1961, Baile and Forbes 1974).
Supplementation alleviates some of these restrictions through increased
passage rates
1985,
(Westra and Christopherson 1976,
Kennedy et al.
1986),
Branine and Galyean
increased efficiency of rumen microbes
(Kennedy et al. 1976, Kennedy et al. 1982), and increased availability
of nutrients limiting microbial activity (Mir et al. 1986, Clark and
Petersen 1986).
However, relative differences between supplemented and
unsupplemented animals are often small and nonsignificant.
trial,
CMI
for
supplemented
unsupplemented cows was
0.91
cows
%BW.
was
0.95
Turner
%BW
(1985)
During this
while
and
CMI
Dunn
for
(1986)
reported similar values, 1.2 %BW versus 0.99 %BW for supplemented and
unsupplemented cows, respectively.
These small relative differences in
CML between supplemented and unsupplemented animals may be due to two
factors.
First,
IVCMD values were obtained from unsupplemented animals.
This value was used for all cows, regardless of supplement type, for
calculation of forage intake.
increase
digestibility
of
Protein supplements have been shown to
feedstuffs
(Campling et al. 1962, Egan 1965).
above
unsupplemented
animals
This fact would suggest differences
in CME between supplemented and unsupplemented animals.
Fecal output
values estimated from rectal grab samples ranged from 0.98 %BW for CON
45
to
1.06
%BW for EM and these showed significant differences.
To
accurately calculate forage intake, IVCMD values should be determined
for
each
supplement
group.
The
in vitro process may
not be
an
appropriate method for determining differences in digestibility and
forage intake among supplemented and unsupplemented animals.
To obtain
correct digestibility values, nylon bag digestion trials should be run
two
or
three
times
during
unsupplemented animals.
the
trial
for
both
supplemented
and
If neutral detergent fiber was utilized for a
digestibility value it would account for differences in rumen microbial
populations among supplements.
Usirg one IVCMD value for all animals
negated any possible differences in (HE among supplements.
Second, weather variables including ambient air temperature, wind
speed, barometric pressure, and snow cover affect the availability and
quality of nutrient supply
and Smith 1976).
(Thompson 1973, Robertshaw 1974, Malechek
To maintain energetic efficiency, free-roaming cows
adapt foraging strategies to these conditions.
Several studies have
reported CHE increases in response to acute thermal stress (Baile and
Forbes 1974, Weston 1979 1982,
increases
Senft and Rittenhouse 1985).
directly compete with metabolizable energy
grazing, growth, and maintenance.
These
available
for
If energy cannot be repartitioned to
offset thermal stresses or if energy that is repartitioned does not
satisfy
energy demands
then maintenance requirements
are not met.
Supplementation alleviates these strains, but may not be able to offset
increased energy demands.
These two factors; one IVCMD value for all
animals and increased energy demands from thermal stresses, caused (HE
to be expressed in a harrow range during this trial.
It may also be a
•?
46
plausible
ej^lanation
for
the
narrow
range
of
winter
CM
values
total
daily
reported in the literature.
Grazing Behavior
Supplementation
did
not
significantly
influence
grazing time, grazing time per interval or distance travelled per day.
Results from these data substantiate forage intake responses.
of C M
to DGT are
11.3+.58% to
unsupplemented animals,
10.1+.72%
respectively.
Ratios
for supplemented versus
This indicates supplementation
increases efficiency of obtaining forage by increasing intake per unit
tine spent grazing.
Distance
supplemented
travelled
with
per
either
day
bypass
showed
similar
protein
or
responses.
energy
Cows
travelled
less
compared to unsupplemented cows.
The exception to this trend were the
SBM
km/d.
cows
which
travelled
5.3
Possibly,
SBM
was
meeting
requirements more efficiently than CON, but not as efficiently as the
other supplements.
This would allow for increased distance travelled
per day over CON cows but still maintain relatively high forage intake
and grazing time.
trends of DGT.
Grazing times per interval followed the general
Supplemented cows grazed less from 0701-1300 and 1901-
0700 than CON cows.
grazing interval.
The exception to this response was the 1301-1900
Here, supplemented cows grazed more than CON cows.
Environmental conditions experienced from 1301-1900 were normally less
stressful
than
supplementation
during
increased
other
grazing
efficiency
of
intervals.
obtaining
forage;
Assuming
grazing
47
regimens for supplemented animals were not as strict as unsupplemented
animals.
Therefore, a greater percentage of grazing occurred during
the 1301-1900 interval.
Arnold and Dudzinski (1978) reported daylength
was usually correlated with less stressful environmental conditions and
these
factors
influenced
initiation
and duration
of daily grazing
intervals.
Although supplementation decreased daily grazing times, declines
were
relatively
suggested
small
grazing
(CON
times
grazed
operated
2.6%
similar
longer
to
each
range
day).
forage
This
intake.
Activity (including grazing and walking) has been suggested as the most
expendable sink for metabolizable energy in the short-term (Senft and
Ritterihouse 1985).
Assuming CON cows represented maximum grazing times
during the winter months, supplementation decreased grazing times below
this maximum threshold.
This was consistent but inverse t& the effects
of supplementation on range forage intake.
Calf Birthweiqht, Cow Bodvweiqht and Condition Score
Calf birthweight was unaffected by supplement, although CON cows
had numerically smaller calves
(38.6 kg).
(37.8 kg)
than supplemented animals
Prepartum cow body weight change was
significant with
supplemented cows having reduced losses (-14.5 kg) compared to CON cows
(-44.4 kg).
Condition score followed similar trends.
CON cows lost
significantly more condition units compared to supplemented groups.
The bypass supplements
either CON or SEM,
(EM, CGM,
and FAT)
possibly due to
lost less condition than
increased efficiency of
rumen
48
microbes related to improved protein and energy status in the small
intestine (Miner 1986).
Trial 2. 1987
Determining environmental effects on winter foraging strategies
for free-ranging cows requires an intensive labor investment in data
collection and
proposed
as
laboratory analyses.
means
for
overcoming
Mathematical models have been
these
restrictions.
This
trial
utilized components of models developed by Senft and Rittenhouse (1985)
and Johnson et al.
stress
(1987)
for determination of short-term thermal
(SITS) and wind-chill temperature
(WCT) to further analytical
\
interpretation of these data.
Thermal acclimation of free-ranging beef cattle is a continual
V
'i
process that changes with differing environmental conditions.
air
temperature
temperatures
conditions
and
is
a
major
metabolic
(Webster 1970).
factor
rates
of
Acute or
influencing
animals
lower
under
Ambient,
critical
free-ranging
short-term cold exposure has
immediate effects on thermal metabolic rates in contrast to chronic
cold exposure, which persists for a longer duration and induces a new
acclimation
state.
Senft
and
Rittenhouse
(1985)
used
short-term
thermal stress (STTS) as a means for determining acclimation lengths of
forage intake and grazing behavior for beef cattle throughout a year.
This indice represented deviations of present days temperature from a
hypothetical acclimated temperature.
Wind speed has been suggested as
aggravating the affects of temperature
(Ames 1974, Ames and Insley
49
1975).
At cold temperatures,
(Webster 1970)
1979).
wind
induces higher heat production
and a higher metabolic
Johnson et al.
rate
(Christopherson et al.
(1987) developed a model utilizing wind-chill
temperature (WCT) to determine the effects of wind speed in combination
with temperature on forage intake of grazing steers.
quantified
response
acclimation
to
ambient
lengths
air
for
winter
temperature
or
Few studies have
foraging
wind
strategies
speed.
This
in
trial
attempted to quantify the effects of STTS and WCT on both daily range
forage organic matter intakes and daily grazing times of free-ranging
prepartum cows for acclimation lengths of I to 20 days.
Forage Intake
Short-term thermal stress increased daily range forage organic
matter intake for acclimation lengths of I, 2, and 3 days.
times (4 to 20 days) did not affect C M .
similar
responses.
acclimation lengths
The
of
first
4 to
three
Wind-chill temperature showed
lag
days
increased
20 days had no affect.
responses of intake to WCT were smaller than to STTS.
be two explanations for this response.
Other lag
CM
but
In general,
There appear to
First, when calculating WCT, .
ambient air temperature was weighted more heavily in the equation than
wind speed and therefore had a more pronounced effect on C M .
during the trial wind speed and STTS had an
Second,
inverse relationship.
During times of significant SITS, wind was almost nonexistent; when
wind
speed
was
high,
the
effects
from
STTS
were
minor.
relationship lasted for the duration of the entire trial period.
This
50
Observed
increases
in
CM
in
relation
to
STTS
and
WCT
for
acclimation lengths of I, 2, and 3 days disagreed with data reported by
Adams et al.
(1986).
They concluded forage intake was reduced during
adverse winter weather.
These discrepancies may relate to times when
research was conducted and methodology.
Adams et al.
(1986) obtained
forage intake data from November 16, 1983 to December 9, 1983.
matter intake declined from 12.1 to 6.8 kg/d.
and consistent throughout the study period.
used for total fecal collections.
CM
Dry
This decline was linear
In addition, steers were
from rectal grab samples is
calculated based on fecal output from total fecal collections and the
ratio of chromic oxide recovery from total collections compared to grab
samples.
If accurate C M values are to be obtained, animals of similar
sex, breed, age, and weight should be used.
Body weights of the steers
were 390 kg compared to two age groups of cattle used for rectal grab
samples, six 3-yr-olds and six 6-yr-olds, who weighed 466 and 545 kg,
respectively.
In addition, using six animals from one age group may
not represent a big
enough sample size due to limited degrees of
freedom (Cordova et al. 1978).
Intake values were significantly higher
from November 28 to December 16 than from December 19 to December 30.
These data support a hypothesis that during late fall to early winter,
animals
are
developing
a
thermoneutral
zone
and
lower
critical
temperature for winter conditions and metabolically adjusting to lower
quality forage; therefore forage intake values decline.
During the
present trial 2, forage intake was obtained from January 10 to February
28 using sixteen 5-yr-old pregnant cows.
and contributed rectal grab samples.
All animals wore fecal bags
Utilizing animals of the same age
51
and
approximately the
same weight
(550
involved in range nutrition studies.
kg)
reduces the variation
Forage intake remained constant
(0.92 %BW) except during periods of STTS or WCT.
returned to normal after 72 h.
an
established
thermoneutral
However, OMI regimes
During this time period, animals have
zone
and
lower
critical
temperature.
These two studies examined two distinct acclimation periods for freeranging cattle.
forage
Once animals are acclimated to winter conditions,
intake remains relatively constant; when
involved in winter
acclimation, intake declines.
Higher
intakes
may
fuel
increases
in
heat
production
maintains homeothermy under stressful thermal conditions.
Blaxter
(1964)
which
Joyce and
and Webster and Blaxter (1966) reported increases in
heat production may take anywhere from 30 minutes to 3 h to reach
equilibrium.
In this trial increased CMI lasted up to 72 h in response
to SITS, which suggested shorter acclimation lengths than previously
proposed.
Senft and Ritterihouse (1985) reported cattle physiologically
acclimated to the mean temperature regime experienced from the previous
11 days.
In their analysis, any day with significant wind speed or
precipitation was
results
because
excluded from the model.
reactions
to wind
increases in absolute temperature.
determine
the
additive
temperature on C M .
effects
speed
This may have
are
felt
skewed,
as .declines
or
In this trial, WCT was assumed to
of
wind
speed
Acclimation lengths, for C M
and
ambient
air-
in relation to STTS
and WCT were similar, indicating the effects of wind speed were already
incorporated
into
the
STTS
equation.
If
free-ranging cattle
are
reacting to absolute temperature changes, then surface body temperature
52
should
be
directly
measured
to
accurately
represent
the
thermal
environment animals are experiencing.
Daily Grazing Time
Behavioral acclimation has been proposed as a means for offsetting
STTS
(Senft and Rittenhouse 1985).
Grazing times during intervals
within a day have decreased in response to rapid increases or decreases
in ambient air temperature (Dunn 1985).
times remained constant.
However, total daily grazing
Little is known about the effects of wind on
grazing behavior and the acclimation process.
For this trial, both
STTS and WCT for acclimation lengths of I to 20 days were analyzed to
determine
effects
on
daily
grazing
time
and
grazing
time within
specified intervals.
As with CM!, STTS for acclimation lengths of only I, 2, and 3 days
influenced DGT.
However, in contrast to CM,. responses were negative.
A similar pattern for WCT was seen.
grazing time.
positive
The first three lag days decreased
This agrees with Malechek and Smith (1976) who found a
correlation
between
daily
grazing
and
air
temperature.
Specifically, reducing the minimum daily temperature from 0 to -40 C
resulted in approximately a 50% reduction in DGT.
lag day 14 also decreased grazing time.
In addition, WCT for
This apparent deviation from
other responses may be due to Type I error in data analysis (Steele and
Torrie 1960).
When alpha levels are set at the .05 level, 95 percent
of the time results received are correct.
-Hinp results are incorrect.
However, 5 percent of the
This 5 percent rejects the hypothesis that
53
thermal stresses (both STIS and WOT) of the previous 3 days influenced
CMI and DCT under winter environmental conditions.
With nearly 2,000
possible combinations of daily grazing times and acclimation lepgths,
this
type
of
error
could
realistically
occur.
Furthermore,
high,
coefficients of variation for grazing behavior data (15 to 25%) lends
credence to this explanation.
If grazing time parallels forage intake, then grazing times should
have increased in response to STTS and WCI.
However, because of the
negative effects of STTS and WCI on grazing time and apparent inverse
relationship between CMI and DCT under thermal stresses;
animals either increased bite rate or bite size.
it appears
The coarse fibrous
nature of winter forage, constant mouth size of animals, and moderate-'
to-light stocking rates of the study pasture diminish the possibility
for increased bite size.
Therefore, bite rate seems a more logical
explanation for increased CMI and decreased in DCT in relation to STTS
and WCI.
stresses
amount
If
animals
increased biting rates
during
acute thermal
(SITS and WCT), then more forage was obtained in a shorter
of
time
temperatures.
which
This
may
minimized
also
thermal
explain
drains
grazing
supplemented compared to unsupplemented animals,
on
time
body
core
decreases
in
even though forage
intake values for supplemented animals were higher.
Grazing times
responses.
for different grazing intervals showed different
Grazing times from 0701-1300 were unaffected by STTS and
WCI for all acclimation lengths.
From 1301-1900 STTS for acclimation
lengths of ,8 to 20 days decreased grazing times.
significant
and
larger
responses
were
In general, the more
associated
with
increased
54
acclimation lengths.
From 1901-0700, grazing times showed positive and
negative responses to STIS.
thermal stress.
as
daily
Positive responses may not constitute
If grazing times per interval follow the same pattern
grazing
tine, . one
would
expect
values
to
decrease.
Considering acclimation lengths of 17 to 20 days showed increases,
these values may relate more to additive effects of STTS on grazing
time than significant thermal stresses.
Grazing times from 1301-1900
were significant under WCT for acclimation lengths of I and 19 days.
Again, lag day 19 had a positive response, possibly relating to Type I
error.
During
the
nighttime
grazing
interval
(1901-0700),
WCT
decreased grazing times for acclimation lengths 3, and 8 to 20 days.
This indicated wind speed was more thermally stressful at night because
the warming effects of sunshine were absent.
Long and short wave
radiation may play substantial roles in successful adaptation to acute
thermal stresses.
Influence of Fecal Bags on Daily Grazing Time
Several variables influence grazing behavior of free-roaming beef
cows.
Some include forage quality and quantity, social facilitation,
previous grazing experience,
variables.
Studies have
stage of production,
reported grazing times
and environmental
for various
free-
roaming and confined settings under numerous environmental conditions.
Forage intake values have also been reported for various settings and
conditions.
Many of these data are obtained through the use of total
fecal collections.
Quite often forage intake data are obtained from
55
different animals than those used for grazing behavior collections.
In
some instances, steers are used for total fecal collections while cows
are used for grazing behavior collections (Adams et al. 1984).
may
lead to discrepancies
in data
This
interpretation due to different
physiological demands of the animals.
Few studies have determined the
influence of fecal bags on grazing behavior.
During this trial, four
groups of four cows wore fecal bags for 96 h collections in January and
February.
All
animals
also
wore
vibracorders
and
pedometers
to
estimate daily grazing time and distance travelled during that time.
The presence of fecal bags decreased total daily grazing time by
24.2 minutes or 4.8%.
unaffected
by
fecal
Grazing times from 1301-1900 and 1900-0700 were
bags.
However,
decreased 10.7 minutes or 7.4% of 6 h.
grazing
from
0701-1300
During this interval,
bags were heaviest prior to being changed at 1130 h.
output
values
ranged
from
20
to
30
kg/d
per
was
fecal
Typical fecal
animals
and visual
observations indicated that cows grazed and travelled less during this
interval.
To determine the real influence of fecal bags on grazing time, one
should relate forage intake declines to daily grazing times.
Assuming
cows took 50 to 60 bites per minute (Funston 1987), each bite gathered
0.5 g of forage
(Leaver 1985) and fecal bags decreased DGT by 24.2
minutes; this represented .605 to 726 grams of lost material per day.
Over a 96 h total fecal collection period, 2.4 to 2.9 kg of forage were
lost.
Obviously, fecal bags have substantial effects on both grazing
behavior and forage intake.
However, total fecal collections are the
most
best
widely
accepted
and
available
collection
device
for
56
estimating
forage
intake
under
free-roaming
conditions.
Until
different methods acceptable for range' conditions are developed., data
interpretation should include adjustment values
fecal bags.
for animals wearing
57
SUMMARY
In trial I, supplementation did not significantly influence winter
foraging strategies of free-roaming pregnant cows.
Supplemented cows
lost significantly less body weight and condition than control cows.
Numerically,
forage intake increased and daily grazing time decreased
for supplemented animals but relative differences from control cows
were small and nonsignificant.
Calf birthweights did not significantly
differ between supplemented and control animals.
months,
forage
I stressful.
quality
These two
is
low
and
During the winter
environmental
factors combine to
limit
conditions
forage
intake
are
and
I
grazing behavior responses to supplementation.
range
forage
It was concluded that
intake and grazing behaviors were expressed within a
narrow potential range under winter forage quality and environmental
restrictions.
minimum
Supplementation elevated these foraging strategies above
thresholds
for
free-roaming
prepartum
cows
grazing
native
range.
During trial 2, all cows acclimated to short-term thermal stress
and wind-chill temperature within 72 h.
x and
daily
responses
grazing
were
significance.
showed
time
small
decreased
and
to
interpreted
Range forage intake increased
acute
as
having
Grazirg times from 0701-1300,
variable
responses.
Generally,
associated with larger acclimation lengths.
thermal
stresses
little
but
biological
1301-1900 and 1901-0700
increased
responses
were
In summary, free-roaming
prepartum cows are relatively unaffected by short-term thermal stress
58
and wind-chill
temperature.
When these
reacclimation occurs within 72 h.
stresses are
experienced,
Under STIS and WCT, forage intake
and grazing behavior are inversely correlated.
The presence of fecal bags decreased daily grazing time by 24.2
\
minutes. Grazing times from 1301-0700 were unaffected by the presence
of fecal bags.
Grazing time from 0701-1300 was decreased 10.7 minutes
by the presence of fecal bags due to increased bag weight prior to
changing at 1130 h.
It was concluded that total fecal collections have
a pronounced negative effect on total daily grazing times and grazing
times up to six hours prior to changing bags.
59
RECOMMENDATIONS
In hindsight, several things might have been changed during these
trials to increase the accuracy and precision of data collection.
trial I, cows body weight values had very high standard errors.
In
The
method of weighing involved moving animals out of the study pasture,
feeding hay and water overnight, then weighing all animals the next
day.
If all cows were weighed in the study pasture standard errors
would probably be lowered.
Durirg trial 2, cows were weighed twice
weekly which increased accuracy; however, snow, wind and animal feces
often biased weights.
I suggest an enclosed scalehouse or enclosure of
the entire chute used for data collection.
During trial I chromic oxide was combined with supplements then
fed.
Failure
supplements
to
probably
achieve
even
influenced
concentrations
forage
intake
in
the
values.
different
This
was
especially true for the animal fat supplement. In addition, cows were
supplemented on alternate days.
Diurnal and daily variations in the
excretion of chromic oxide would also influence forage intake values.
This problem was eradicated during trial 2 when all cows were bolused
daily with 10 g chromic oxide in a gelatin capsule.
In trial I rectal grab samples were taken from all 61 cows at the
sane time as total fecal collections.
However, fecal bag cows were
grabbed first and then the rest of the cows were grabbed.
These time
lags may have influenced the amount of chrpmic oxide in the feces.
If
fecal excretion curves could be determined for the animals this would
60
account for some of the variation in sampling method.
In addition, if
all cows could be grabbed before being supplemented it would increase
accuracy of fecal chromium concentrations.
One consistent problem between trials was estimation of distance
travelled.
This factor could explain considerable variation in grazing
efficiency between normal conditions and acute thermal stresses.
If
pedometers are utilized, then more accurate correction factors should
be used.
Bite rate should be quantified during the winter months.
This may
help explain forage intake increases to acute thermal stress although
grazing time decreases.
Measurement of the body surface temperature of
animals would give a clearer indication of the thermal regimes animals
are experiencing.
Possibly electrodes could be inserted into eartags
and monitored with a computer system.
indication of thermal regimes.
This would give a realistic
If body core temperatures were also
measured, this may give an indication of the heat production of the
animal.
Cattle used for total fecal collections should become familiar with
fecal bags at least one month before collections start.
This would
decrease expenditures spent on new bags and repair of old bags.
It may
also
become
allow
for
more
accurate
collections
as
the
animals
accustomed to wearing a fecal bag.
A complete processing of samples as soon as they are collected
would expedite the graduation process.
Laboratory procedures should be
formally outlined with all necessary equipment in good working order.
In addition,
computers
should be available
for use
at all
times.
61
Ccmputer accounts should include enough space and money to enhance
rather than restrict data analysis.
Two or three computers should be
available and reserved for graduate student use.
This would reduce the
student demand on computers that are being used by major professors.
It would also allow graduate students with more computer expertise to
assist those with fewer skills.
These skills are used throughout our
graduate program but are often deficient because of low computer access
and available assistance.
62
REFERENCES CITED
63
REFERENCES CITED
Adams, D. C. 1984. Time of day and interval of supplementation for
beef cattle grazing fall-winter range. Proc. Montana Nutr. Conf.
p p . 14.1. _
Adams, D. C. 1985. Effect of time of supplementation on performance,
forage intake and grazing behavior of yearling beef steers grazing
Russian wild ryegrass in the fall. J. Anim. Sci. 61:1037.
Adams, D. C. 1986. Winter grazing activity and forage intake of range
cows in the northern great plains. J. Anim. Sci. 62:1240.
Adams, D. C., R. E. Short and B. W. IOiapp. 1987. Body size and body
condition effects on performance and behavior of grazing beef cows.
Nutr. Reports Inti. 35:269.
Allsion, C. D. 1985. Factors affecting forage intake by ruminants: a
review. J. Range Manage. 38:305.
Ames, D. R. 1974. Wind-chill factors for cattle and sheep. In:
Livestock Environment, Eroc. Inti. Livestock Environment Symposium.
Amer. Soc. Agr. Eng., St. Joseph, MI.
Ames, D. R. 1986. Assessing the impact of climate. In: Gary P. Moberg
(ed.). Limiting the effects of stress on cattle. West. Reg. Res.
Pub. #009 and Utah Ag. Exp. Sta., Utah State University, Logan, U T .
Ames, D. R. and L. W. Insley. 1975. Wind-chill effects for cattle and
sheep. J. Anim. Sci. 40:161.
\
Ames, D. R. and D. E. Ray. 1983. Environmental manipulation to improve
animal productivity. J. Anim. Sci. 7:209.
Anderson, D. M. and N. S. Urquhart. 1986. Using digital pedometers to
monitor travel of cows grazing arid rangeland. Appl. Anim. Beh.
Sci. 16:11.
Arnold, G. W. 1984. Regulation of forage intake. In: R. J . Hudson and
r . g . White (eds.) Bioenergetics of wild herbivores, pp. 87-88. CRC
Press, Inc., Florida.
Arnold, G. W. and M. L. Dudzinski. .1978. Ethology of the Free-ranging
Domestic Animal. Elsevier, New York.
64
Association of Official. Agriculture Chemists (AOAC). 1980. Official
methods of analysis (13th ed.) Assoc. Off; A g r . Chem. Washington,
D. C. ■ -
Baile, C. A. and J. .M. Forties. 1974. Control of feed intake and
. regulation of energy balance in ruminants. Physiological Reviews.
54:160.
Bellows, R. A. and R. E. Short. 1978. Effects of precalving feed level
on birth weight, calving difficulty and subsequent fertility. .J.
Anim. Sci. 46:1522.
Bellows, R. A., R. E. Short and G. V. Richardson. 1982. Effects of
sire, age of dam and gestation feed level on dystocia and
postpartum reproduction. J. Anim. Sci. 55:18.
Bellows, R. A. and 0. 0. 'Thomas. 1976. Some effects of supplemental
grain feeding on performance of cows and calves on range forage.. J.
Range Manage. 29:192.
Bines, I. A. 1971. Metabolic and physical control of food intake in
ruminants. Proc. Nutr. Soc. 30:116.
Blaxter, K. L. and F. W. Wainman. 1961. Environmental temperature and
the energy metabolism and heat emission of steers. J, Agric. Sci.
56:81.
Blaxter, K. L. and R. S. Wilson. 1963. The assessment of a crop
husbandry technique in terms of animal production. Anim. Prod.
5:27.
Branine, M. E. and M. L. Galyean. 1985. Influence of supplemental grain
on forage intake, rate of passage and rumen fermentation in steers
grazing summer blue grama rangeland. Proc. West. Sec. Amer.' Soc.
Anim. Sci. 36:290.
Campling, R. C. and C. C. Balch. 1961. Factors affecting the voluntary
feed intake of the cow. I. Preliminary observations on the effect
on the voluntary intake of hay, and changes in the amount of the
reticulo-rundnal contents. Brit. J. Nutr. 15:525.
Campling, R. C., M. Freer and C. C. Balch. 1962. Factors affecting the
voluntary intake of food by cows. Brit. J. Nutr. 16:115.
Campling, R. C. and J. C. Murdoch. 1966. The effect of concentrates of
the voluntary intake of roughages by cows. J. Dairy Res. 33:1.
\ Christopherson, R. J. 1976. Effects of prolonged cold and the outdoor
winter environment on apparent digestibility in sheep and cattle.
J. Anim. Sci. 56:201.
65
Christqpherson, R. J. 1985. The thermal environment and the ruminant
digestive system. In: M. K. Yousef (ed.) Stress physiology in
livestock. Volume I. Basic principles, pp. 163-180. CRC Press,
Inc., Florida.
Christopherson, R. J., R. J. Hudson and M. K. Christopherson. 1979.
Seasonal energy expenditures and thermoregulatory responses of
bison and cattle. Can. J. Anim. Sci. 59:611.
Christopherson, R. J., J. R. Thompson, V. A. Hammond and G. A. Hills.
1978.
Effects of thyroid status on plasma adrenaline and
noradrenaline concentrations in sheep during acute and chronic cold
exposure. Can. J. Physiol. Pharmacology. 59:490.
Christopherson, R. J. and B. A. Young. 1981. Heat flow between large
terrestrial animals and the cold environment. Can. J. Chem. Eng.
59:181.
Christopherson, R. J. and B. A. Young. 1986. Effects of cold
environments on domestic animals. In: Grazing research at Northern
Latitudes. (Ed.) Olafur Gudmondsson. Plenum Publishing Corporation,
pp. 247-257.
Clanton, D. C. 1981. Crude protein system in range supplements. In:
Owens, A.L. ed. PTotein Symposium. Oklahoma State University, p.
'
10.
Clanton, D. C. and D. R. Zimmermann. 1965. Protein levels in beef cow
wintering rations. PToc. West. Sec. Am. Soc. Anim. Sci. 16:LXXX.
Clanton, D. C. and D. R. Zimmermann. 1970. Symposium on pasture methodsfor maximum production in beef cattle. J. Anim. Sci. 36:310.
Clark, C. K. and M. K. Petersen. 1986. Influence of amino acid or
branch chain organic acids on in vitro fermentation of winter range
forage. Proc. West. Sec. Amer. Soc. Anim. Sci. 36:310.
Cook, C. W. and L. E. Harris. 1950. The nutritive value of range forage
as affected by vegetation type, site and state of maturity. Utah
Ag. Exp. Sta. Bull. 344. Utah State University, Logan, Utah.
Cook, C. W. and L. E. Harris. 1968. Nutritive value of seasonal ranges.
Utah Ag. Exp. Sta. Bull. 472. Utah State University, Iogan, UT.
Cordova, M. K., J. D. Wallace and R. D. Peiper. 1978. Forage intake by
grazing livestock: a review. J. Range Manage. 31:430.
Costigan, P. and K. J. Ellis. 1986. Analysis of faecal chromium derived
from controlled marker devices. New Zealand J. Tech. Res.
66
Curran, M. K., R. C. Campling and W. Holmes. 1967. The feed intake of
milk cows during late pregnancy and early lactation. Anim. Prod.
9:266.
Deswysen, A. G. and H. J. Ehrlein. 1981. Silage intake, rumination and
pseudo-rumination activity in sheep studied by radiography and jaw
movement recordings. Brit. J. Nutr. 46:327.
Dunn, R. W. 1986. Physiological and behavioral responses of cows on
Montana foothill range to winter and supplement. M.S. Thesis.
Montana State University, Bozeman, MT.
Dunn, R. W., K. M. Havstad and E. L. Ayers. 1988. Grazing behavior
responses of rangeland beef cows to winter ambient temperatures and
age. Appl. Anim. Beh. Sci. (accepted).
Dunn, T. G., J. E. Ingalls, D. R. Zimmerman and J. N. Wiltbank. 1969.
Reproductive performance of 2-yr-old Hereford and Angus heifers as
influenced by pre- and post-calving energy intake. J. Anim. Sci.
29:719.
Egan, A. R. 1965. Nutritional status and intake regulation in sheep.
The relationship between improvement of nitrogen status and
increase in voluntary intake of low-protein roughages by sheep.
Aust. J. Agr. Res. 16:463.
Egan, A. R. 1977. Nutritional status and intake regulation in sheep.
VIII. Relationships between the voluntary intake of herbage by
sheep and the protein/energy ratio in the digestive products. Aust.
J. Agric. Res. 16:279.
Elliot, R. C. and J. H. Topps. 1963. Voluntary intake of low protein
diets by sheep. Anim. Prod. 5:269.
Ellis,
W.
C.
1978. Determinants of
digestibility. J. Dairy Sci. 61:1828.
grazed
forage
intake
and
Fenton, T. W. and M. Fenton. 1979. An improved procedure for the
determination of chromic oxide in feed and feces. Can. J . Anim.
Sci. 59:631.
Forbes, J. M. 1969. The effect of pregnancy and fatness on the volume
of rumen contents in the ewe. J. Agric. Sci. (Camb). 72:119.
Forbes, J. M. 1970. The voluntary food intake of pregnant and lactating
ruminants: a review. Brit. Vet. J. 126:1.
Funston, R. N. 1987. Grazing behavior of rangeland beef cattle
differing in biological type. M. S. Thesis, Montana State
University, Bozeman, MT.
67
Furr, R. D. and A. B. Nelson. 1964. Effect of level of supplemental
winter feed on calf weight and on milk production of fall-calving
range beef cows. J. Anim. Sci. 23:775.
Galyean, M. L. 1985. Laboratory practices in animal nutrition research.
New Mexico State University, Las Cruces, NM. 210 p.
Geisecke, D., W. vonEnglehart and H. Erbersdobler. 1975. Tracer studies
on non protein nitrogen in ruminants, vol. 2. Vienna IAEA p. 133140.
Goetsch, A. L., F. N. Owens and M. A. Funk. 1984. Effects of nitrogen
source on site of digestion in dairy cows and in semi-continuous
rumen cultures. Nutr. Reports Inti. 30:881.
Gonyou, H. W., R. J. Christopherson and B. A. Young. 1979. Effects of
cold temperature and winter conditions on some aspects of behavior
of feedlot cattle. Appl.'. Anim. Ethology. 5:113.
Graham, N. Me. and A. J. Williams. 1962. The effects of pregnancy on
the passage of food through the digestive tract of sheep. Aust. J .
Agric. Res. 13:894.
Grovum, W. C. 1979. Factors affecting the voluntary intake of food by
sheep. 2. The role of distention and tactile input from
compartments of the stomach. Brit. J. Nutr. 42:425.
Harris, L. E. 1970. Nutritional research techniques for domestic and
wild ruminants. Vol. I. L. E. Harris Pub., Logan, UT.
Havstad, K. M. and J. C. Malechek. 1982. Energy expenditure by heifers
grazing crested wheatgrass of diminishing availability. J. Range
Manage. 35:447.
Heroux, 0. 1969. Catechcolamines, corticosteroids and thyroid hormones
in nonshivering thermogenesis under different
environmental
conditions. In: Baj auz, E. ed. Physiology and pathology of
adaptation mechanisms. Pergamon Press, Oxford, pp. 345-365.
Hironaka, R. and H. F. Peters. 1969. Energy requirements for wintering
mature pregnant beef cows. Can. J. Anim. Sci. 49:323.
Holder, J. M. 1962. Supplementary feeding of grazing sheep and its
affect on pasture intake. Proc. Aust. Soc. Anim. Prod. 4:154.
Johnson, H. D. 1976. Progress in biometeorology: the effect of weather
and climate on animals. Div. B. Volume I. Part I. Swets and
Zeitlinger B.V., Amsterdam.
Johnson, M. E., W. C. Russell and J. D. Hansen. 1987. Effect of
environment on forage intake of grazing steers - a model. Nutr.
Reports Inti. 36:1081.
68
Jones, S. D. M., M. A. Price and R. T. Berg. 1979. Effect of winter
weight loss in Hereford cows on subsequent calf performance to
weaning. Can. J. Anim. Sci. 59:635.
Jordan, W. R., E. E. Lister and G. J. Rowlands. 1968. Effect of planes
of nutrition on wintering pregnant beef cows. Can. J. Anim. Sci.
48:145.
Joyce, J. P. and K. L. Blaxter. 1964. The effect of air movement, air
temperature and infra-red radiation on the energy requirements of
sheep. Brit. J. Nutr. 18:5.
Kartchner, R. J. 1981. Effects of protein and energy supplementation of
cows grazing native winter range forage intake and digestibility.
J. Anim. Sci. 51:432.
Kartchner,- R. J. and L. R. Rittenhouse. 1979. A feces-urine separator
for making total fecal collections from the female bovine. J. Range
Manage. 32:404.
Kato, S. and B. A. Young. 1984. Effects of cold exposure on pancreatic
endocrine secretions in sheep. Can. J. Anim. Sci. 64 (Suppl.l) :263.
Kennedy, P. M. 1985. Influences of cold exposure on digestion of
organic matter, rates of passage of digesta in the gastrointestinal
tract and feeding and rumination behavior in sheep given four
forage diets in the chopped, or ground and pelleted form. Brit. J .
Nutr. 53:159.
Kennedy, P. M., R. J. Christopherson and L. P. Milligan. 1976. The
effect of cold exposure of sheep on digestion, rumen turnover time
and efficiency of microbial synthesis. Brit. J. Nutr. 36:231.
Kennedy, P. M., R. J. Christopherson and L. P. Milligan. 1982. Effect
of cold exposure on feed protein degradation, microbial protein
synthesis and transfer of plasma urea to the rumen in sheep. Brit.
J. Nutr: 47:521.
Kennedy, P. M., R. J. Christopherson and L. P. Milligan. 1986.
Digestive responses to cold. In: L. P. Milligan, W. L. Grovum and
A. Dobson (eds.). Control of digestion and metabolism in ruminants.
Proc. Sixth Inti. Sym. on Ruminant Physiology. Prentice Hall,
Englewood Cliffs, New Jersey, pp. 285-306.
Kennedy, P. M. and L. P. Milligan. 1978. Effects of cold exposure on
digestion, microbial synthesis and nitrogen transformations in
sheep. Brit. J. Nutr. 39:105.
LaMontagne, F. A. D. 1981. Response of cull cows to different ration
concentrate levels. M. S. Thesis, Montana State. University,
Bozeman, MT.
69
Leaver, J. D. 1985. Milk production from grazed temperate grassland. J.
Dairy Sci. 52:313.
Leinkert, W., M. Witt, E. Parries and R. Djamala. 1966. Studies of
weight changes and feed intake at the end of pregnancy and the
beginning of lactation. Nutr- Abst. and Reviews. 37:262.
Lesperance, A. L., V. R. Bohman and D. W. Marble. 1960. Development of
techniques for evaluating grazed forage. J. Dairy Sci. 43:682.
Low, W. A., R. L. Tweedie, C. B. H. Edwards, R. M. Hodder, K. W. J.
Malafant and R. B. Cunningham. 1981. The influence, of environment
on daily maintenance behavior of free-ranging shorthorn cows in
central Australia. I. General introduction and descriptive analysis
of day long activities. Appl. Anim. Ethology. 7:11.
Lusby, K. S., D. F. Stevens, L. Khori and R. Totusek. 1976. Effects of
winter supplement level on roughage intake and digestibility of
three breeds of cows in drylot. Oklahoma Ag. Exp. Sta. Res. Rep.
MP-26. p. 19.
Malechek, J. C. and B. M. Smith. 1976. Behavior of range cows in
response to winter weather. J. Range Manage. 29:9.
Marsh, H., K. F. Swingle, R. R. Woodward, G. F. Payne, E. E. Frahm, L.
H. Johnson and J. C. Hide. 1959. Nutrition of cattle on an eastern
Montana range as related to weather, soil and forage. Montana Ag.
Exp. Sta. Bull. 549.
Miner, J. L. 1986. Bypass supplementation of grazing pregnant beef
cows. M.S. Thesis. Montana State University, Bozeman, MT.
Mir, P. S., Z. Mir and J. A. Robertson. 1986. Effect of branched- chain
amino acids or fatty acid supplementation on in vitro digestibility
of barley straw or alfalfa. Can. J. Anim. Sci. 66:151.
Monfejt h , J. L. and L. E. Mount. 1974. Heat loss from animals and man.
Butterworths, London.
Mount, L. E. 1979. Adaptation to Thermal Environment.NUniv. Park Press,
Baltimore.
National Oceanic and Atmospheric Association. 1986. Climate of Montana.
Vol. 89(1).
National Research Council (NRC). 1984. Nutrient requirements of
cattle. National Academy Press, Washington, D.C.
beef
Osuji, P. O. 1974. The physiology of eating and the energy expenditure
of the ruminant at pasture. J. Range Manage. 27:437.
70
Owenz J. B., E. L. Miller and P. S. Bridge. 1968. A study of the
voluntary intake of food and water and the lactation performance of
cows given diets of varying roughage content ad libitum. J. Agric.
Sci. 70:223.
Petersen, M. K. and D. C. Clanton. 1981. Bypass protein (blood meal) in
winter range supplements for the grazing beef cow and weaned calf.
Proc. West. Sec. Amer. Soc. Anim. Sci. 23:18.
Putnam, P. A. and J. Bond. 1971. Drylot feeding patterns
reproducing beef cow. J. Anim. Sci. 33:1086.
for the
Raleigh, R. J. and J. D. Wallace. 1963. Effect of supplementation on
intake of grazing animals. Proc. West. Sec. Amer. Soc. Anim. Sci.
14: XXVII.
Raleigh, R. J., R. J. Kartchner and L. R. Rittenhouse. 1980. Chromic
oxide in range nutrition studies. Oregon State University. Ag. Exp.
Sta. Bull. 641.
Reid, C. S. W. 1965. Quantitative studies of digestion in the reticulorumen. I. Total removal and return of digesta for quantitative
sampling in studies of digestion in the reticulo-rumen of cattle.
New Zealand Soc. Anim. Prod. Proc. 25:65.
Rittenhouse, L. R. 1969. The influence of supplemental protein and
energy on intake and digestibility of winter range forage. Fh. D.
Dissertation, University of Nebraska, Lincoln.
Rittenhouse, L. R., D. C. Clanton and C. L. Streeter. 1970. Intake and
digestibility of winter-range forage by cattle with and without
supplements. J. Anim. Sci. 31:1215.
Ritterihouse, L. R. and R. L. Senft. 1982. Effects of daily weather
fluctuations on the grazing behavior of cattle. FToc. West. Sec.
Amer. Sci. 33:305.
Robertshaw, D. 1974. Environmental physiology. Physiology Series One.
Volume 7. University Park Press, Baltimore, Maryland.
Robinson, J. J. and J. M. Forbes. 1967. A study of the protein
requirements of the mature breeding ewe. 2. Protein utilization in
the pregnant ewe. Brit. J. Nutr. 21:879.
Ross, R. L. and H. E. Hunter. 1976. Climax vegetation of Montana based
on soils and climate. USDA Soil Conservation Service (SCS),
Bozeman, MT., 61 p.
Russell, A. J. F., J. N. Peart, J. Eadie, A. J. McDonald and I. R.
White. 1979. The effect of energy intake during late pregnancy on
the production from two genotypes of suckler cow. Anim. Prod.
28:309.
71
SAS User's Guide, 1985 Edition. SAS Institute, Inc., Cary, NO. 956 p.
Senft, R. L. and L. R. Rittenhouse. 1985.
acclimation in cattle. J. Anim. Sci. 61:297.
A
model
of
thermal
Siebert, B. D. and R. A. Hunter, 1981. Supplementary feeding of grazing
animals. In: J. B. Hacker (ed.) Nutritional limits to animal
production from pastures, pp. 409-426. Commonwealth Agricultural
Bureaux, F a m h a m Royal.
Smith, T. M . , A. L. Iesperance, V; A. Bohman, R. A. Breckbill and R. W.
Brown. 1968. Intake and digestibility of forages grazed by cattle
on a southern Nevada range. Rroc. West. Sec. Amer. Soc. Anim. Sci.
19:277.
Steele, R. G. D. and J. H. Torrie. 1960. Principles and Procedures of
Statistics. McGraw-Hill Book Co., Inc. p. 67-71.
Stobbs, T. H. 1970. Automatic measurement of grazing time by dairy
cows on tropical grass and legume pastures. Trop. Grasslands.
4:237.
Thompson, G. E. 1973. Review of the progress of dairy science: Climatic
physiology of cattle. J. Dairy Res. 40:441.
Topps, J. H. 1972. Urea or biuret supplements to low protein grazing in
Africa. World Anim. Rev. 3:14.
Turner, M. E. 1985. The forage intake of supplemented cows grazing
winter foothill rangelands of Montana. M. S. Thesis, Montana State
University, Bozeman.
VanDyne, G. M. and D. T. Torrell. 1964. Development and use of the
esophageal fistula: a review. J. Range Manage. 17:7.
Ward, M. G., D. C. Adams, R. E., Short and B. W. Knapp. 1987. Body size
arii body condition effects on performance and behavior of grazing
beef cows. In: Ft. Keogh Livestock and Range Research Station Field
Day. pp. 13-16.
Warren, W. P., F. A. Marks, K. H. Asay, E. S. Hildebrand, C. G. Payne
and J. R. Vogt. 1974. Digestibility and rate of passage by steers
fed tall fescue, alfalfa and orchardgrass in 18 and 32 C ambient
temperatures. J. Anim. Sci. 39:93.
Webster, A. J. F. 1970. Direct effects of cold weather on the energetic
efficiency of beef production in different regions of Canada. Can.
J. Anim. Sci. 50:563.
Webster, A. J. F. and K. L. Blaxter. 1966. The thermal regulation of
two breeds of sheep exposed to air temperatures below freezing..
Res. Vet. Sci. 7:466.
72
Weston, R. H. 1979. Feed intake regulation in the sheep. In: J. L.
Black and R. J. Reis (eds.) Physiological and environmental
limitations to wool growth, pp. 163-177. Univ. New England Publ.
Unit, Armidale, Aust.
Weston, R. H. 1982. Animal factors affecting feed intake. In: J. B.
Hacker (ed.) Nutritional limits to animal production from pastures,
pp. 183-198. Commonwealth Agricultural Bureau, U.K.
Westra, R. and R. J. Christopherson. 1976. Effects of cold on
digestibility, retention time of digesta, reticulum motility and
thyroid hormones in sheep. Can. J. Anim. Sci. 56:699.
Whitman, R. W. 1975. Weight change, body condition and beef-cow
reproduction. Eh. D. Dissertation, Colorado State University, Ft.
Collins.
Wiltbank, .J. N., W. W. Rowden. J. E. Ergalls, K. E. Gregory and R. M.
Kock. 1962. Effects of energy level on reproductive phenomena of
mature Hereford cows. J. Anim. Sci. 21:219.
Young, B. A. 1975. Effects of winter acclimatization
metabolism of beef cows. Can. J. Anim. Sci. 55:619.
on
resting
Young,
B. A.
1976. Effects of cold environments on nutrient
requirements of ruminants. Proc. First Inti. Sym. Feed Composition,
Animal Nutrient Requirements and Computerization of Feeds, July 1116, 1976. Utah St. University, Logan, U T . pp. 491.
Young, B. ,A. 1981. Cold stress as it affects animal production. J.
Anim. Sci. 52:154.
Young, B. A. 1986. Food intake of cattle in cold climates. In: 1986
Feed intake symposium. Oklahoma City, Oklahoma.
Young, B. A. and R. J. Christopherson. 1974. Effect of prolonged cold
exposure on digestion and metabolism in ruminants. Int. Livestock
Env. Syirp., Amer. Soc. Agr. Eng., St. Joseph, pp. 75.
Young, B. A. and J. L. Corbett. 1972. Maintenance energy requirements
of grazing sheep in relation to herbage available. I. Calorimetry
estimates. Aust. J. Agric. Res. 23:57.
Zinn, R. A. and F. N. Owens. 1981. Influence of level of feed intake on
digestive function. I. Nitrogen metabolism. Oklahoma Ag. Exp. Sta.
Oklahoma State University, Stillwater, OK. USDA-SEA-AR.
73
APPENDIX
\
74
Table 12.
Chromic oxide analysis procedure, Trials I and 2a .
Step
Description
1
Tabp-1 test tubes (borosilicate 100 ml) in
numerical order using heat marker.
2
Weigh .2 g sample into tubes (duplicate samples).
3
Ash overnight at 450 C in muffle furnace.
4
Allow tubes to cool 5-10 minutes.
5
Place four glass beads (3 mm) into tubes to prevent
bumping.
6
Ad 1.5 ml chromium digestion solution (600 ml
distilled H2O, 600 ml sulfuric acid, 800 ml 70%
perchloric acid, 40 g sodium molybdate) with
repipet dispenser.
7
Place aluminum plate over hot plate (see Figure I).
8
Turn on hot plate to 150 C for 1-1.5 h or until
majority of sairples are a yellow to orange color.
9
Slowly turn up hot plate in 25 C increments every
30 -minutes (maximum temperature reached should be
500 C).
10
Remove samples from hot plate when 8 mm fluid is
left in tubes.
11
Allow to cool 15-20 minutes under acid hood.
12
Add 8 ml distilled H2O to each tube and vortex for
uniformity.
13
Centrifuge tubes for 5 minutes at 1500 rpm.
14
Read tubes on flame spectrophotometer at 400 nm
using tungsten lamp, purge with distilled H2O
between each sample
aModified from Fenton and Fenton (1979) and Costigan and Ellis (1986).
75
Table 13.
Chromic oxide fed (g/d) and recovery (% as fed)
from total fecal collections and rectal grab samples
for each supplement, Trial I.
Supplement
fed (g/d)
Recovery (% as fed)
Rectal Grab
Total Fecal
Samples
Collections
SEM
19.65
85.8
68.2
EM
16.07
107.3
90.9
CCM
13.48
119.1
95.3
FAT
14.60
116.5
91.0
Table 14. Meansa for esophageal extrusa in vitro organic matter
digestibility (IVCMD) and crude protein (CP), Trial I.
Month
IVOMD
CR
December'
36.5
6.6
January
36.9
7.5
February
36.9
6.1
36.8+2.3
6.9+.95
means+SE
aMeans within a month represent two to three collections of two
to three cows.
76
Table 15.
Daily fecal output (PO, %BW) estimated using total
fecal collections, Cr2Ogz and rectal grab samples
for each supplement, Trial Ia .
Total Fecal
Collections
Cr203 Samples
From Totals
CON
•55b
— —
SBM
.58b
.54b
.98b
BM
.62b
.74c
1.06c
OGM
•59b
.61b
1.00b
.63b
1.03b
.083
.035
I
Supplement
FAT
SEd
.025
Rectal Grab
Samples
—
aLeast-Suqares means.
^cMeans in the same column differ (Pc.05).
^Pooled standard error of the least-squares means.
Table 16.
Supplement
Initial, final and change in cow body weight (kg)
and condition score for each supplement, Trial Ia .
Body Weight (kg)
Change
Initial
Final
Condition Score
Change
Initial
Final
CON
488.2b
449.5b
-38.Tb
4.28b
3.33b
-0.95b
SBM
496.5b
478.8b
-17.7C
4.51b
3.58b
-0.93d
BM
504.5b
500.Ob
-4.5C
4.31b
3.85b
—0.46c
CGM
486.3b
475.5b
-10.Se
4.39b
3.7(fi
—0.69c
FAT
504.8b
493.6b
-11.2°
4.55b
3.92b
-0.63c
19.6
13.2
.178
.338
.122
SEe
8.7
aLeast-squares means.
bed Means in the same column differ (Pc.05).
ePooled standard error of the least-squares means.
77
Table 17.
Qiromic oxide (Cr2Oa) recovery (% as fed)a per cow
from total fecal collections and rectal grab samples
Trial 2.
Recovery ,(% as fed)
Total Fecal
Rectal Grab
Collections
Sanples
Cow
2019
74.1
71.4
2043
79.4
72.5
2052
77.5
72.3
2063
74.1
67.1
2065
71.4
66.2
2069
76.3
65.4
2084
80.0
76.3
2085
75.8
69.9
2099
75.8
66.8
2119
73.5
68.6
2138
70.4
62.1
2177
71.9
64.3
2179
83.1
85.2
2209
69.4
66.3
2241
104.5
94.7
2248
75.2
68.3
77.0
71.1
Mean
aAll cows were bolused with 10 g/d Cr2O3 in a size 10 gelatin
capsule.
78
Table 18.
In vitro organic matter digestibility (IVQMD)
from rumen extrusa for each week, Trial 2a .
■Week
IYOMD
1/04-1/10
31.24
1/11-1/17
35.04
1/18-1/24
36.57
1/25-1/30
34.29
1/31-2/07
38.57
2/08-2/14
34.16
2/15-2/22
30.94
2/23-2/28
32i63
MeanfSE
34.13+3.97
aLeast-squares means, P>.05.
x
79
Table 19.
Fecal output (PO, %BW) for each cow for each week
estimated from rectal grab samples. Trial 2a .
■Fecal Output (PO, %BW)
1/25- 1/31- 2/08- 2/151/30
2/07
2/14
2/22
Cow
1/111/17
1/181/24
2019
.637
.560
.584
.535
.534
2043
.642
.568
.559
.538
2052
.514
.481
.490
2063
.644
.580
2065
.701
2069
2/232/28
MeanfSE
.552
.560
.566+.036
.516
.525
.581
.561+.043
.465
.466
.471
.517
.486+.022
.638
.645
.586
.605
.671
.624+.034
.659
.712
.677
.658
.682
.716
.686+.024
.549
.504
.565
.503
.507
.507
.598
.533+.038
2084
.615
.601
.562
.611
.581
.598
.654
.603+.029
2085
.714
.724
.715
.695
.664
.728
.737
.711+.025
2099
.624
.578
.597
.569
.569
.532
.525
.571+.035
2119
.630
.556
.580
.538
.585
.560
.655
.586+.042
2138
.612
.552
.579
.579
.591
.574
.691
.597+.045
2177
.741
.725
.731
.648
.679
.699
.774
.713+.042
2179
.626
.681
.679
.672
.638
.665
.801
.680+.057
2209
.683
.658
.693
.700
.681
.668
.763
.692+.034
2241
.542
.529
.497
.490
.439
.525
.583
.515+.045
2248
.651
.578
.604
.585
.587
.643
.658
.615+.034
Mean .633
.596
.612
.590
.596
.580
.655
SE .061
.073
.075
.076
.074
.077
.089
aLeast-squares means, P>.05.
80
Table 20.
Cow
Initial, final and change in cow body weight (kg)
and condition score. Trial 2.
Body Weic^it (kg)
Initial Final Change
Condition Scores
Initial Final Change
2019
606.5
583.7
-22.8
4.5
3.8
-0.7
2043
561.5
562.5
+1.0
3.8
3.3
-0.5
2052
546.6
523.0
-23.6
4.3
3.5
-0.8
2063
554.3
556.1
+1.8
3.5
3.5
±0.0
2065
528.4
538.9
+10.5
4.3
3.3
-1.0
2069
512.6
501.2
-11.4
4.0
3.5
-0.5
2084
543.4
555.2
/
+11.8
4.0
3.5
-0.5
2085
562.5
542.0
-20.5
4.0
3.5
-0.5
2099
569.3
537.5
-31.8
4.0
3.3
-0.7
2119
537.1
543.9
+6.8
4.0
3.3
-0.7
2138
555.7
528.9
r-26.8
4.8
3.5
—1.3
2177
573.8
559.3
—14.5
4.0
3.8
—0.2
2179
512.6
512.1
-0.5
4.0
3.5
-Oi 5
2209
464.0
450.9
-13.1 '
4.3
3.3
-1.0
2241
628.2
662.2
+34.0
4.3
4.0
-0.3
2248
550.2
541.1
-9.1
4.5
3.3
-1.2
550.4
37.83
543.7
43.71
—6.8
17.41
4.1
.31
3.5
.21
—0.6
.35
Mean
SE
t
81
Table 21.
Distance travelled (km/d) for all cows each week
Trial 2.
Cow
1/61/12
2019
1.2
-'
3.4
3.5
2043
5.2
4.2
4.1
2052
-
2.6
2063
-
2065
3.7
1/12- 1/19'- 1/26-■ 2/21/19 1/26 2/2
2/8
2/82/16
2/162/20
2/202/26
1.7
3.1
4.6
3.4
4.9
2.7
3.4
4.1
7.6
1.8
1.8
-
1.9
1.6
1.8
3.8
2.5
3.2
-
2.2
2.9
2.3
5.6
4.0
-
4.3
5.3
4.0
5.6
2069
2.1 . 3.0
4.5
3.6
2.3
4.3
3.7
5.7
2084
3.1
3.6
3.4
3.8
3.3
5.9
3.1
3.1
2085
4.3
5.0
6.2
-
4.2
3.6
3.9
4.4
2099
4.0
3.7
4.3
3.7
4.2
4.1
4.5
5.5
2119
1.7
4.6
3.0
2.4
3.4
4.0
3.3
1.5
2138
5.2
3.8
4.7
4.1
-
5.5
5.1
8.0
2177
8.4
5.7
-
■ 3.7
1.9
3.6
3.5
4.4
2179
3.8
5.6
4.1
3.9
5.2
5.5
-
5.3
2209
6.0
6.1
4.1
3.7
1.5
5.8
4.5
6.1
2241
3.8
3.1
3.0
3.7
2.3.
1.5
2.1
2.3
2248
.3.4
3.0
3.1
3.2
2.5
2.9
2.4
4.3
4.0
1.8
4.2
1.1
3.7
1.0
3.5
.73
3.1
1.1
3.9
1.4
3.6
.96
4.5
1.9
Mean
SE