acute thermal stresses and supplementation
TRANSCRIPT
Winter foraging behaviors of beef cows in relation to acute thermal stresses and supplementationby Steven Kenneth Beverlin
A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science inRange ScienceMontana 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 andended 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 beefcows to supplementation and winter environmental conditions and (2) to determine acclimation lengthsof winter foraging strategies for free-roaming pregnant beef cattle under short term-thermal andwind-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), comgluten meal (CGM), animal fat (FAT) and range forage only (CON). SBM, CGM, EM, and FATreceived 200 g/d rumen degradable protein. EM and OGM received 200 g/d additional bypass proteinand FAT received 50 g/d additional bypass energy. Two groups of ten cows wore fecal bags for a weekin January and February. Rectal grab samples were obtained from all 61 cows concurrently with totalfecal collections. Four groups of four cows wore vibracorders to estimate daily grazing time in threeintervals: 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 lessweight and condition (P<.05,-14.5 kg, -.68) than CON (-44.4 kg, -.95), respectively. OMI and DGTwere expressed within a narrow potential range under low forage quality and mild environmentalconditions. In 1987, 16 cows of the same genotype as trial 1 wore vibracorders and pedometers usingthe same methods as trial 1. Four groups of four cows wore fecal bags for 96 h collections within aweek in January and February. Rectal grab samples were obtained daily from all cows. All cows werebolused daily with 10 g chromic oxide. Acclimation lengths were determined for daily OMI, DGT, andDGTI under short-term thermal stress (STTS) and wind-chill temperature (WCT). Acclimation lengthsof I to 3 days increased CME (P<.05) and decreased DGT (P<.05) to both STTS and WCT. DGTIshowed variable responses. Generally, larger DGTI responses were associated with longer acclimationlengths. Cows returned to normal CMI and DGT regimes within 72 h. The presence of fecal bagsdecreased 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 tobags being full before being changed prior to 1130 h. Adjustment factors should be made for animalswearing 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
bySteven Kenneth Beverlin
A thesis submitted in partial fulfillment of the requirements for the degree
of
Master of Science
inRange Science
MONTANA STATE UNIVERSITY Bozeman, Montana
April 1988
/3 IUS
APPROVAL
of a thesis submitted by
Steven Kenneth Beverlin
ii
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 - V - V l '%Date
O - T " v \ >Head, Major Department
'XV'M>-.
Approved for the College of Graduate Studies
Date Graduate Dean
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 have assisted with the completion of this thesis project. People of significant importance include: Dr. Kris Havstad, Eldon Ayers, Ed Fredrickson, 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! Sincere thanks also go to Drs. Mark Petersen, John Lacey, Jack Taylor, Brian Sindelar, and Clayton Marlow whose valuable advice made things easier on everyone. Thanks also to Steve Kachman, Kathy Hanford, and Carol Bittinger whose computer expertise kept me "on line". To everyone at the Nutrition Center, especially Dr. Nancy Roth and Connie Clark, thanks for the help and assistance. To the secretaries, Gayle, Pat, Diane, Jo, and Jeanne: "thanks forletting things slide".
Much of the credit for completing this project goes to my family: Mom and Dad, Dave and Jill, and Mike Beverlin. When things got
overwhelming a call home always improved my spirits and eased my burdens. 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 NutritionCenter and the fragrant smells of rumen extrusa and cow s__t. Yourlove and companionship made all it worthwhile.
My heartfelt thanks to all of you for making this journey possible.
V
TABLE OF CONTENTS
PageLEST OF TABLES....................................................viiABSTRACT.... .............................................. ........ ixINTRODUCTION...................................................... ILITERATURE REVIEW................................................. 3
Introduction.................................................. 3Heat Production and Metabolism................................ 5Winter Foraging Strategies.................................... 7Digestive Responses.............. *.......... ................. 11Supplementation............................................... 14Pregnancy...................... 18
MATERIALS AND METHODS............................................. 21
Study Site............................. 21Animals...................... ...................... ........ 22Treatments............... 22Measurements........................................... 24
Grazing Behavior.......... 24Fecal Organic Matter Output.............................. 25Dietary Digestibility............. 26Forage Organic Matter Intake............. '28Body Weight and Condition Score.".......... 29Climatic Conditions...................................... 29
Data Analyses................................................. 29Trial I, 1986.... 29Trial 2, 1987............................ .............. 30
RESULTS.......... 33
Trial I, 1986......................... 33Forage Intake................................... 33Grazing Behavior................................ 34Calf Birthweight, Cow Body Weight and Condition Score..... 35Climatic Conditions...................................... 36
Trial 2, 1987................................................. 37Forage Intake.............. 37Grazing Behavior......................................*.. 39Influence of Fecal Bags on Daily Grazing Times............ 42
vi
TABLE OF CONTENTS - Continued
PageDISCUSSION....................... 43
Trial I, 1986............................................ 43Forage Intake.................... 43Grazing Behavior........................................ 45Calf Birthweight, Cow Body Weight and Condition Score.... 47
Trial 2, 1987......... 48Forage Intake............................................ 49Daily Grazing Time....................................... 52Influence of Fecal Bags on Daily Grazing Time............ 54
SUMMARY................... '.................... ....'.............. 57RECOMMENDATIONS.......................... 5gREFERENCES CITED.............. 62APPENDIX........................................ 73
U S T OF TABLES
Table Page1. Supplement cxmposition (g/d), Trial I................. ........ 232. 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 eachsupplement. 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, anddeviation from normal for each month, Trial I................. 37
7. Significant responses of daily forage organic matter intake (CM %BW, OMB) to short-term thermal stress and magnitude of response (%BW) for acclimation lengths ofI to 20 days, Trial 2......................................... 38
8. Significant responses of daily forage organic matter intake (CM %BW, OMB) to wind-chill temperature and magnitude of response (%BW) for acclimation lengthsof 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 •
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viii
U S T OF TART F-S-Continued
Table . Page13. 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 matterdigestibility (IVOMD) and crude protein (CP), Trial 1......... 75
15. Daily fecal output (PO, %BW) estimated using total fecalcollections, 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 fromtotal fecal collections and rectal grab samples, Trial 2..... 77
18. In vitro organic matter digestibility (IVOMD) from rumenextrusa for each week, Trial 2................................. 78
19. Fecal output (PO, %BW) for each cow for each week estimatedfrom rectal grab samples, Trial 2............................. 79
20. Initial, final and change in cow body weight (kg) andcondition score. Trial 2............................ .......... 80
21. Distance travelled (kr̂ /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 (Cm), 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 1901- 0700 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 forage seldom meets nutrient requirements of grazing livestock. Consumption of available protein and energy by prepartum cows grazing winter range is usually below National Research Council . (1984) recommendations by such magnitude that subsequent reproduction can be impaired (Allison 1985, 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. If prepartum cows can efficiently utilize winter forage and 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 responses for maintenance of homeothermy. Kennedy (1985) stated these responses vary with the temperature of the
environment relative to the lower critical temperature (LCT) of the animal and the duration of cold exposure. Acclimation is associated
with hormonal and metabolic functional changes that develops as a consequence of prolonged cold or heat 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 insight into critical nutritional periods and enable producers to 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. In addition, it is usually deficient in' protein, phosphorus and carotene (Cook et al. 1950, Marsh et al. 1959). 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 by reticulo-rumen volume (gut fill), and rate of disappearance from that organ (Campling and Balch 1961, Baile and Forbes 1974, Ellis 1978, Grovum 1979). 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. In
addition to the constraints of a low quality diet; free-roaming ruminants must adapt foraging strategies to winter environmental conditions to maintain energetic efficiency.
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The climatic environment acts on animals to influence thermoregulation as well as affecting the availability and quality of nutrient supply (Thompson 1973, Robertshaw 1974). Osuji (1974) stated that environmental stress, including energy costs of grazing and walking, may raise the maintenance requirement 25 to 50% above that of indoor animals. Other studies. Young and Corbett (1972) and Havstad and Malechek (1982), believed this increase ranged from 40 to 70%. Comparisons 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, there are few studies addressing affects of the
winter environment on foraging strategies and the time course of
acclimation to winter environmental variables. 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 supplementation and pregnancy effects on winter foraging strategies, body weight and body condition.
5
Heat Production and Metabolism
The thermal state of an animal at any instant in time is a consequence of its prior thermal exposure, rate of 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 lower critical temperature (LCT). Christopherson and Young (1981) defined the TNZ as a range of environmental temperatures in which an animal, without additional energy expenditures above -the maintenance requirement, can readily
alter the rate of heat loss from the body. 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 body heat to the environment and aid in the maintenance of homeotherrny. 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 increase metabolic heat production to achieve thermal balance. Cattle adapt morphologically and physiologically to achieve an acclimation state in response to environmental conditions. Chronic cold exposure (one week or longer) results in an increased resting metabolic rate associated with increased resting metabolic heat production. Young and Christopherson (1974) 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 (Gonyou et al. 1979) which are powered by free fatty acids (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. However, energetic costs of these adaptations result in a persistently higher rate of heat production which leads to increased feed requirements.
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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). This shift in intake apparently arises from two basic sources: (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). IXiring STIS metabolic heat production increases to compensate
for a faster rate of heat loss to the environment. The animal compensates for this increased metabolic demand by increasing food intake. Senft and Ritterihouse (1985) reported if animals are exposed to temperatures within their thermoneutral zone, feed intake should be independent of environmental temperature. However, if temperatures
drop below the LCT, animals increase forage 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. The level of intake also influences the LOT. As
metabolic rates increase during SITS, increased intake allows for increased heat production and the LCT decreases. This agrees with Mount (1979) and Ames and Ray (1983) who stated at extremely cold temperatures intake increased to meet thermoregulatory needs. In contrast to this, Senft and Rittenhouse (1985) and Malechek and Smith
(1976) reported intake decreased in response to daily temperature
changes from an acclimation temperature. Also, Dunn (1986) reported
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, and when the studies were conducted during the year (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, Christopherson 1985). This increased metabolic
energy demand, along with elevated thyroid levels, potentially increases appetite drive and may allow for increased intakes. Although the effects of chronic cold exposure are significant, 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
8
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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
to more favorable microenvironments or repartition metabolizable energy
for thermoregulation.
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 would minimize heat transfer to the environment. In contrast to the above findings. Low et al. (1981) stated very little of the seasonal changes in grazing behavior may be explained by variations in temperature, rainfall, solar radiation or wind. Timing of activities could be affected by these factors. 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 (1982) suggested the ability of cattle to regulate grazing time 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). Although behavioral acclimation offsets thermal strain, mechanisms involved may not compensate enough for conditions encountered.' 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. Most of these responses are related to duration of cold exposure and whether an animal is acclimated to winter environmental conditions.
During cold exposure (either acute or chronic) digestibility is reduced. Westra and 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 increased (Westra and Christopherson 1976, Kennedy et al. 1986). 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 of cold exposure are higher reticular contraction rates. During both short-term and chronic cold stress, increased rates of reticular contractions were reported for cattle and sheep (Westra and Christopherson 1976, Gonyou et al. 1979, . Kennedy 1985). 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. Geisecke et al. (1975) hypothesized the omasum is selective for particulate passage 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. 1974) and shorter rumen turnover time (Kennedy et al. 1976). The reduction in retention time significantly alters the amount of cell wall constituents (CWC) and organic matter (CM) degraded. Kennedy et al. (1976) reported apparent digestion of CM for 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, which shows improved efficiency of rumen microbes. 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.
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Because digestion in the reticulo-rumen is reduced, Kennedy (1985) examined the possibility of increased intestinal digestion. Cold exposure did not increase digestibility of CWC or CM in the gastrointestinal tract; however, volatile fatty acids changed in proportion to the reduction of CM digested. Specifically, there was a decrease in acetic acid and increase in propionic acid which agrees with similar work conducted by Kennedy et al. (1976) and Kennedy and Milligan (1978). 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. These increases may arise from either
increased flow of digesta from the reticulo-rumen (and thus more
dietary protein escaping fermentation), increased 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). Digestive changes help maintain the nitrogen balance of the animal. 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).
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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. Supplementation provides additional nutrients in an attempt to offset these deficiencies.
Supplementation
Reproductive performance of the beef cow is closely aligned with■ Inutritional 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 is usually below NRC (1984) recommendations by such magnitude that subsequent reproduction is impaired (Allison 1985, Cordova et al. 1978). 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 effective it must complement forage
digestion by rumen microbes. 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 supplementation may allow for optimization of microbial protein synthesis and increase the digestible protein received from range forage alone (Zinn and Owens 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 (Kennedy et al. 1976) or increases (Kennedy and Milligan 1978). If this is the case and forage is available, supplementation may 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. However, responses vary with both the year and type of supplement (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 protein supplementation increases intake of a low protein feed (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). More recent studies (Goetsch et al. 1984) have shown both increased and decreased microbial efficiency. Although studies have shown both positive and negative intake responses to protein supplementation,
strong evidence shows that small amounts of supplemented protein increases intake when forage quality is low. 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. Although nighttime grazing does occur, it is extremely variable and 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. 1968, Lusby et al. 1976, Russel et al. 1979). 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 conditions of undemutrit ion. Pre-calving
supplementation is dependent upon body condition and post-calving
nutrition. Poor pre-calving nutrition may be tolerated if post-calving nutrition 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. 1967, Owen et al. 1968,
Forbes 1969, Putnam and Bond 1971). Leinkert et al. (1966) showed a
significant correlation between the 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 the extent to which the rumen can stretch. In early pregnancy, roughage intake may be maintained or even increase even
although the 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. Other logical reasons include preoccupation with birth, 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. Ward et al. (1987) compared body weight and condition changes of large and
small 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. Body condition also influences reproductive capability.
Whitman (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 appears that producers should
maintain cows in good body condition (approximately 5 on a I to 10 scale) entering the winter to enhance postpartum reproductive
20
capability and facilitate adaptations to winter environmental conditions.
<!
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 I was initiated December 15, 1985 and concluded March 6, 1986. Trial 2 began December 15, 1986 and ended February 28, 1987. Both trials were conducted on a 324 ha pasture with long north-facing slopes and areas of steep slopesand 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). Dominant grasses include bluebunch wheatgrass
fAqroovron spicatum), needleandthread (Stipa comata), Idaho fescue fFestuca idahoensis) and basin wildrye (Elvmus cinereus). Shallow
sites surrounding rocky outcrops contained ponderosa pine (Pirns oonderosa), limber pine CPinus flexilus) and Rocky Mountain juniper (Juniperus scopulorum). Turner (1985) provides a complete list of
species found at Red Bluff Research Ranch.
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 were various combinations of Angus X Hereford and(or) Tarentaise. Initial mean body weight and condition score (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: soybean meal (SBM), bloodmeal (BM), c o m gluten meal (Cm), animal fat (FAT), and control (GON),
which received range forage only (Miner 1986). Composition of each supplement is listed in Table I. All supplements contained 200 g/d
rumen degradable protein. This satisfied 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.
Protein Availability Supplement g fed g.CP g TDN Bypass(g) Rumen(g)
SBM 570 250 430 50 200EM 230 200 340 160 40SBM 450 200 40 40 160
Total 680 400 480 200 200CGM 450 290 370 190 100SBM 140 60 100 10 50
Urea 16 50 0 0 50Total 606 400 470 200 200
FAT 210 0 410 0 0SBM 570 250 430 50 200
Total 780 250 840 50 200CON _ _ _ — —
aEach supplement group also contained 50 g dried molasses and 4.5 g Molasses Booster (Feed Flavours, Inc.)
and GGM were sources of bypass protein from an animal and plant
source, respectively. 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 com) used as an
external marker for determination of fecal organic matter output (Raleigh et al. 1980). Supplements were fed individually on alternate
days at approximately 1130 h.Throughout trial 2 all cows grazed native range without
supplementation. 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 intramuscularly with 20,000,000 IU Vitamin A. In addition, all cows had access to a loose iodized salt mixture containing 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). Each day was divided into three grazing intervals: 0701-1300, 1301-1900 and
1901-0700. These intervals were chosen to represent morning, afternoon
and nighttime grazing periods. In trial 2, all cows (n=16) wore
vibracorders to estimate DGT for the same intervals as trial I. Both
years, animals wore the same vibracorder throughout the trial. Vibracorder charts were changed weekly at 1130 h. Charts were read as hours grazed per interval (DGTI), rounded to 15 minutes. Total DGT was the sum of DGIT for each interval for each day. No other activity
levels were assigned.Distance travelled per day (DT) was estimated using pedometers
(Anderson and Urquhart 1986). 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. Rectal grab samples for Cr2O3 analysis
were collected from all 61 cows at the same time as total, fecal
collections.Durirg trial 2, total fecal collections were obtained from four
groups of four cows (n=16) using the same methodology as trial I.
Collections (96 h) were obtained from each group within a week in January and a week in February. Samples were collected daily at 1130
h. Rectal grab samples were obtained daily at 1130 h from all cows for
26
For both trials, collected total fecal material was weighed, mixed, sampled and frozen. . Rectal grab samples were immediately frozen. 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). An outline of this method is presented in Appendix Table 12. FO per day was estimated from rectal grab samples based on the following eguation: gF0/d= [ (g Cr2O3 fed per day)/(Cr2O3 (%) in dry fecal sample) ]. Two adjustments were made to this original value. For trial I, Cr2O3 recovery per supplement was calculated and the quantity of Cr2O3 fed
per day was adjusted accordingly. Values were also adjusted for each supplement group using PO estimates from total fecal collections (Rittenhouse 1969, Rittenhouse et al. 1970). For trial 2, rectal grab
samples were adjusted individually for each cow based on PO from total
fecal collections.\
Dietary Digestibility
During trial I, samples of grazed forage were collected using three esophageal-fistulated cows (VanDyne and Torrell 1964). Collections were obtained periodically throughout the trial (Appendix
Cr2O3 analysis. In addition, all cows were bolused daily with 10 g
Cr2O3 in a gelatin capsule (size #10)..
27
Table 14). Samples of grazed forage for trial 2 were collected weekly with four rumen-fistulated cows using a total evacuation technique (Iesperance et al. 1960). Animals were penned overnight without feed or water. The 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. Animals were then gathered, cannulas were removed and rumen contents were removed, mixed, subsampled and frozen. Initial rumen contents were returned to the rumen and cows were released. All cows used for digestibility estimates grazed concurrently with other research animals. For both trials, extrusa was frozen then freeze-dried and ground. In vitro organic matter digestibility (IVCMD) of each sample was determined
using the Bames 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 (Galyean 1985).
28
Forage Omanic Matter Intake
Forage organic matter intake (CMC), was estimated using the following equation: CMC= [daily FO (kg) / (I-IV(MD) ]. 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 forageorganic 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 Adjusted Cr2O3 fed per day
BxCxF/A=G kg fecal output per day
H Adjustment factor per supplement comparing recovery of Cr2O3 from total collections with rectal grab samples
GxH=I Adjusted fecal output
J Body weight (kg)
(I/J)XlOO=K Fecal output as % of body weight
L Forage digestibility (IVCMD)
I/1-L=M Total forage organic matter intake (kg/day)
(IVJ)XlOO=N 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, supplement, and individual cow within 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). Dependent variables included calf weight, and body weight and cow condition change per supplement. Independent variables included supplement, individual cow and the supplement by cow interaction. 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. L values of I to 20 days were
chosen to approximate values of 9-14 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 day (Txnin(i+1)): Ti=
[ (2^max(I) )+ (%Ln(i))+ (Tmin(i+l))]/4- ^TTS on day i was defined as the difference between Tj and the hypothetical acclimated temperature
[TaccI (i)]: STTS= [ (Ti)-(Taccl(i)) ] • Responses of OH, DGT and DGTI to STTS for L values of I to 20 d were analyzed. Dependent variables in the model were CMC, DGT and DGTI. Indepenient variables included individual cow, SITS, and individual cow by STTS. The model was tested with individual cow by STTS as the error term. In addition to STTS, the effect of wind-chill temperature (WCT) 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: WCT= [(-1.4109)-(.00334*wind) +
(.995*temp) + (.000013*wind)2]. Wind speed (km/d) was averaged daily
and averaged per grazing interval while SITS was utilized as the temperature value. 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. Independent variables included individual cow, week of the trial, presence or absence of
32
fecal bags and the individual cow by fecal bag interaction. The model was tested against individual cow by bag as the error term.
33
RESULTS
Trial I. 1986
Forage Intake
, There were no differences (P>.05) in forage organic matter intake (%BW, OMB) between supplements (Table 3). Average CMI for all supplements was 0.94 %BW. BM and FAT had the highest OMI, 0.98 and 0.95 BW, respectively. OGM, SBM, and 00N were lower and consistent, ranging from 0.91 to 0.93 %BW. IVCMD was estimated at 36% during the trial. 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.
SupplementOMI+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. Average Cr2Og recovery from rectal grab samples was 86.4%. Mean recovery per supplement ranged from 68.2 to 95.3%. Cr203 fed per day and mean recovery per supplement from rectal 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. These times represented 44.8%, 65.7%, and 18.7% of the hours available for grazing in each interval, respectively. 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. Average distance travelled per day for all supplements was
4.6 tan/d. SEM and CON walked the farthest, 5.3 km/d and 5.1 W d ,
respectively.
35
All supplement groups had one 3-, 4-, 5-, and 6-yr-old cow wearing a vibracorder and a pedometer throuc^iout the study. Due to statistical limitations and the study objectives, 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 0701-1300 1301-1900
(h)1901-0700
DistanceTravelled(kny/d)
CON 9.04b 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
OGM
%nCO 2.68b 4. Ilb 2.13b 4.Ib
FAT 8.33b 2.69b 3.88b 2.20b 4.Ob
SEc .19 S .21 .31 .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
CalfBirthweight
(kg)i ' -
Body Weight Change (kg)
ConditionScoreChange
CONr37.8b -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-termaverage, and deviation from normal for each month.Trial I.
MonthTemperature
(C)Long-term
Average (C)Deviation
From Normal
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
Mean +0.4 -0.9 +1.3SE 2.8 1.9 1.2
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
38I to 3 days increased CMI (P<.05) by .0002 to .0005 %BW. No other acclimation lengths were significant. Again, normal CMI regimes
Table 7. Significant responses of daily forage organic matterintake (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)
Magnitude of Response (%BW)
I ** +.0003
2 ** +.0003
3 * +.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 CMI for various acclimation lengths although responses were small. 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 from rumen extrusa is
presented in Appendix Table 18. 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). Grazing times from 0701-1300 were
unaffected (R>.05) by STTS. 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. For 1901-0700 responses were both positive and negative. This 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. Acclimation lengths of I, 2, 3, and 14 days affected DCT (P<.05). This follows the trends of STTS and WCT on CHE, and SITS on DCT. Responses of DCT to WCT were small, ranging from .002 to .007 h/d. Grazing times from 0701-1300
Table 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.
Acclimation Length Period (d) .
Daily0701-0700
Grazing Intervals (h)1301- 1901- 0701-1900 0700 1300
I * (-.010)2 , ** *** (-.003) •3 * (-.005)4 ■56 * (-.0001)78 * (-.0005) * (+.0002)9 ** (-.0006)10 ** (-.0006)11 ■** (-.0006)12 *** (-.0006)13 *** (-.0006)14 *** (-.0007) * (-.0008)15 *** (-.0007)16 *** (-.0007)17 *** (-.0006) * (+.0001)18 *** (-.006) * (+.0003)19 *** (-.007) * (+.001)20 *** (-.005) * (+.001)
*P<.05**P<.01***P<.0bl
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. Each response was negative (-.0007 to -.011 h/d), possibly showing increased wind 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 Grazing Intervals (h)Length Daily 1301- 1901- 0701-Period (d) 0701-0700 1900 0700 1300
I * (-.007) * (-.002)2 ** (-.003)3 * (-.005) * (-.005)45678 * (-.007)9 * (-.006)10 ** (-.006)11 ** (-.006)12 ** (-.007)13 *** (-.007)14 * (-.010) *** (-.007)15 ** (-.007)16 ** (-.008)17 ** (-.007)18 ** (-.007)19 * (+.001) ** (-.009)20 *** (-.011)
*P<.05**P<.01***Pk.001
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)1301-19001901-07000701-1300
aIeast-squares means. ***P<.001
8.49+1.294.17+0.67
2.12+0.992.40+0.73
*** -24.2
- 12.0 +35.7
*** -10.7
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. Typical fecal
output values ranged from 20 to 30 kg/d per animal and visual observations indicated that cows travelled and grazed less when bags
were full.Distance travelled per day in weekly intervals is listed in
Appendix Table 21.
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. Rittenhouse (1970) reported intake of 1.0 %BW for cattle on winter range in Nebraska. Dunn (1986), using the same pasture and supplements, had an average OMI of 1.25 %BW. Individual supplements influenced CMI in
various ways. EM, a bypass protein source, had the highest forage
intake. 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. FAT, a bypass
energy source, had the second highest OMI. 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 (Westra and Christopherson 1976, Branine and Galyean 1985, Kennedy et al. 1986), 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. During this
trial, CMI for supplemented cows was 0.95 %BW while CMI for
unsupplemented cows was 0.91 %BW. Turner (1985) and Dunn (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. Protein supplements have been shown to
increase digestibility of feedstuffs above unsupplemented animals
(Campling et al. 1962, Egan 1965). 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 the trial for both supplemented and unsupplemented animals. 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 (Thompson 1973, Robertshaw 1974, Malechek and Smith 1976). 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, Senft and Rittenhouse 1985). These increases directly compete with metabolizable energy available for
grazing, growth, and maintenance. 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 C M values reported in the literature.
Grazing Behavior
Supplementation did not significantly influence total daily grazing time, grazing time per interval or distance travelled per day. Results from these data substantiate forage intake responses. Ratios
of C M to DGT are 11.3+.58% to 10.1+.72% for supplemented versus unsupplemented animals, respectively. This indicates supplementation increases efficiency of obtaining forage by increasing intake per unit tine spent grazing.
Distance travelled per day showed similar responses. Cows supplemented with either bypass protein or energy travelled less
compared to unsupplemented cows. The exception to this trend were the SBM cows which travelled 5.3 km/d. 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. Grazing times per interval followed the general trends of DGT. Supplemented cows grazed less from 0701-1300 and 1901-
0700 than CON cows. The exception to this response was the 1301-1900
grazing interval. Here, supplemented cows grazed more than CON cows. Environmental conditions experienced from 1301-1900 were normally less stressful than during other grazing intervals. Assuming supplementation increased efficiency of obtaining forage; 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 small (CON grazed 2.6% longer each day). This
suggested grazing times operated similar to range forage 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 (37.8 kg) than supplemented animals (38.6 kg). 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 (EM, CGM, and FAT) lost less condition than either CON or SEM, possibly due to 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 laboratory analyses. Mathematical models have been proposed as means for overcoming these restrictions. This trial utilized components of models developed by Senft and Rittenhouse (1985) and Johnson et al. (1987) for determination of short-term thermalstress (SITS) and wind-chill temperature (WCT) to further analytical
\
interpretation of these data.
Thermal acclimation of free-ranging beef cattle is a continualV
'i
process that changes with differing environmental conditions. Ambient, air temperature is a major factor influencing lower critical temperatures and metabolic rates of animals under free-ranging
conditions (Webster 1970). Acute or 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, wind induces higher heat production (Webster 1970) and a higher metabolic rate (Christopherson et al. 1979). Johnson 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. Few studies have quantified acclimation lengths for winter foraging strategies in response to ambient air temperature or wind speed. This trialattempted 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. Other lag times (4 to 20 days) did not affect CM. Wind-chill temperature showed
similar responses. The first three lag days increased C M but acclimation lengths of 4 to 20 days had no affect. In general, responses of intake to WCT were smaller than to STTS. There appear to
be two explanations for this response. 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 CM. Second, during the trial wind speed and STTS had an inverse relationship.
During times of significant SITS, wind was almost nonexistent; when wind speed was high, the effects from STTS were minor. This relationship lasted for the duration of the entire trial period.
50
Observed increases in C M 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. Dry matter intake declined from 12.1 to 6.8 kg/d. This decline was linear and consistent throughout the study period. In addition, steers were used for total fecal collections. C M 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. All animals wore fecal bags
and contributed rectal grab samples. Utilizing animals of the same age
51
and approximately the same weight (550 kg) reduces the variation involved in range nutrition studies. Forage intake remained constant (0.92 %BW) except during periods of STTS or WCT. However, OMI regimes returned to normal after 72 h. During this time period, animals have an established thermoneutral zone and lower critical temperature. These two studies examined two distinct acclimation periods for free- ranging cattle. Once animals are acclimated to winter conditions, forage intake remains relatively constant; when involved in winter acclimation, intake declines.
Higher intakes may fuel increases in heat production which maintains homeothermy under stressful thermal conditions. Joyce and Blaxter (1964) 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 excluded from the model. This may have skewed,
results because reactions to wind speed are felt as . declines or
increases in absolute temperature. In this trial, WCT was assumed to
determine the additive effects of wind speed and ambient air-
temperature on CM. Acclimation lengths, for C M 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). However, total daily grazing times remained constant. 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. The first three lag days decreased grazing time. This agrees with Malechek and Smith (1976) who found a positive 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. In addition, WCT for lag day 14 also decreased grazing time. 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. However, 5 percent of the -Hinp results are incorrect. 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; it appears animals either increased bite rate or bite size. 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. If animals increased biting rates during acute thermal
stresses (SITS and WCT), then more forage was obtained in a shorter amount of time which minimized thermal drains on body core temperatures. This may also explain grazing time decreases in supplemented compared to unsupplemented animals, even though forage
intake values for supplemented animals were higher.Grazing times for different grazing intervals showed different
responses. 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. In general, the more significant and larger responses were associated with increased
54
acclimation lengths. From 1901-0700, grazing times showed positive and negative responses to STIS. Positive responses may not constitute
thermal stress. If grazing times per interval follow the same pattern as daily 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, stage of production, and environmental
variables. Studies have reported grazing times 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). This may lead to discrepancies in data 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%. Grazing times from 1301-1900 and 1900-0700 were unaffected by fecal bags. However, grazing from 0701-1300 was decreased 10.7 minutes or 7.4% of 6 h. During this interval, fecal
bags were heaviest prior to being changed at 1130 h. Typical fecal output values ranged from 20 to 30 kg/d per 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 widely accepted and best 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 for animals wearing fecal bags.
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. During the winter months, forage quality is low and environmental conditions are
I stressful. These two factors combine to limit forage intake andI
grazing behavior responses to supplementation. It was concluded that range forage intake and grazing behaviors were expressed within a
narrow potential range under winter forage quality and environmental restrictions. Supplementation elevated these foraging strategies above minimum 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. Range forage intake increased
x and daily grazing time decreased to acute thermal stresses but
responses were small and interpreted as having little biological significance. Grazirg times from 0701-1300, 1301-1900 and 1901-0700 showed variable responses. Generally, increased responses were associated with larger acclimation lengths. In summary, free-roaming prepartum cows are relatively unaffected by short-term thermal stress
58
and wind-chill temperature. When these stresses are experienced, reacclimation occurs within 72 h. 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. In trial I, cows body weight values had very high standard errors. 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 to achieve even concentrations in the different supplements probably influenced forage intake values. 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. This would give a realistic indication of thermal regimes. 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 allow for more accurate collections as the animals become
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.
61Ccmputer 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
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73
APPENDIX
\
74
Table 12. Chromic oxide analysis procedure, Trials I and 2a.
Step Description
1
2345
6
78
9
10
1112
1314
Tabp-1 test tubes (borosilicate 100 ml) in numerical order using heat marker.Weigh .2 g sample into tubes (duplicate samples).Ash overnight at 450 C in muffle furnace.Allow tubes to cool 5-10 minutes.Place four glass beads (3 mm) into tubes to prevent bumping.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.Place aluminum plate over hot plate (see Figure I).Turn on hot plate to 150 C for 1-1.5 h or until majority of sairples are a yellow to orange color.Slowly turn up hot plate in 25 C increments every 30 -minutes (maximum temperature reached should be 500 C).Remove samples from hot plate when 8 mm fluid is left in tubes.Allow to cool 15-20 minutes under acid hood.
Add 8 ml distilled H2O to each tube and vortex for uniformity.Centrifuge tubes for 5 minutes at 1500 rpm.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 samplesfor each supplement, Trial I.
Supplement fed (g/d)
Recovery Total Fecal Collections
(% as fed) Rectal Grab Samples
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
means+SE 36.8+2.3 6.9+.95
aMeans within a month represent two to three collections of two to three cows.
76
Table 15. Daily fecal output (PO, %BW) estimated using totalfecal collections, Cr2Ogz and rectal grab samplesfor each supplement, Trial Ia .
SupplementTotal Fecal Collections
Cr203 Samples From Totals
Rectal Grab Samples
CON • 55b — — —
SBM .58b .54b .98bBM .62b .74c 1.06cOGM • 59b .61b 1.00bFAT I .63b 1.03b
SEd .025 .083 .035aLeast-Suqares means.^cMeans in the same column differ (Pc.05).^Pooled standard error of the least-squares means.
Table 16. Initial, final and change in cow body weight (kg) and condition score for each supplement, Trial Ia.
Body Weight (kg) Condition ScoreSupplement Initial Final Change Initial Final Change
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
SEe 8.7 19.6 13.2 .178 .338 .122
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 cowfrom total fecal collections and rectal grab samplesTrial 2.
Recovery ,(% as fed) Total Fecal Rectal Grab
Cow Collections Sanples
2019 74.1 71.42043 79.4 72.52052 77.5 72.32063 74.1 67.12065 71.4 66.22069 76.3 65.42084 80.0 76.32085 75.8 69.92099 75.8 66.82119 73.5 68.62138 70.4 62.12177 71.9 64.32179 83.1 85.22209 69.4 66.32241 104.5 94.72248 75.2 68.3
Mean 77.0 71.1aAll cows were bolused with 10 g/d Cr2O3 in a size 10 gelatin capsule.
78Table 18. In vitro organic matter digestibility (IVQMD)
from rumen extrusa for each week, Trial 2a.
■ Week IYOMD
1/04-1/10 31.241/11-1/17 35.041/18-1/24 36.571/25-1/30 34.291/31-2/07 38.572/08-2/14 34.162/15-2/22 30.942/23-2/28 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.
Cow1/18-1/24
■Fecal Output 1/25- 1/31-1/30 2/07
(PO, %BW) 2/08- 2/14 MeanfSE
1/11-1/17
2/15-2/22
2/23-2/28
2019 .637 .560 .584 .535 .534 .552 .560 .566+.0362043 .642 .568 .559 .538 .516 .525 .581 .561+.0432052 .514 .481 .490 .465 .466 .471 .517 .486+.0222063 .644 .580 .638 .645 .586 .605 .671 .624+.0342065 .701 .659 .712 .677 .658 .682 .716 .686+.0242069 .549 .504 .565 .503 .507 .507 .598 .533+.0382084 .615 .601 .562 .611 .581 .598 .654 .603+.0292085 .714 .724 .715 .695 .664 .728 .737 .711+.0252099 .624 .578 .597 .569 .569 .532 .525 .571+.0352119 .630 .556 .580 .538 .585 .560 .655 .586+.0422138 .612 .552 .579 .579 .591 .574 .691 .597+.0452177 .741 .725 .731 .648 .679 .699 .774 .713+.0422179 .626 .681 .679 .672 .638 .665 .801 .680+.0572209 .683 .658 .693 .700 .681 . 668 .763 .692+.0342241 .542 .529 .497 .490 .439 .525 .583 .515+.0452248 .651 .578 .604 .585 .587 .643 .658 .615+.034Mean .633 .596 .612 .590 .580 .596 .655
SE .061 .073 .075 .076 .074 .077 .089aLeast-squares means, P>.05.
80
Table 20. Initial, final and change in cow body weight (kg) and condition score. Trial 2.
Body Weic^it (kg) Condition ScoresCow Initial Final Change Initial Final Change
2019 606.5 583.7 -22.8 4.5 3.8 -0.72043 561.5 562.5 +1.0 3.8 3.3 -0.52052 546.6 523.0 -23.6 4.3 3.5 -0.82063 554.3 556.1 +1.8 3.5 3.5 ±0.02065 528.4 538.9 +10.5 4.3 3.3 -1.02069 512.6 501.2 -11.4 4.0 3.5 -0.52084 543.4 555.2/ +11.8 4.0 3.5 -0.52085 562.5 542.0 -20.5 4.0 3.5 -0.52099 569.3 537.5 -31.8 4.0 3.3 -0.72119 537.1 543.9 +6.8 4.0 3.3 -0.72138 555.7 528.9 r-26.8 4.8 3.5 —1.32177 573.8 559.3 —14.5 4.0 3.8 —0.22179 512.6 512.1 -0.5 4.0 3.5 -Oi 52209 464.0 450.9 -13.1 ' 4.3 3.3 -1.02241 628.2 662.2 +34.0 4.3 4.0 -0.32248 550.2 541.1 -9.1 4.5 3.3 -1.2Mean 550.4 543.7 —6.8 4.1 3.5 —0.6
SE 37.83 43.71 17.41 .31 .21 .35
t
81Table 21. Distance travelled
Trial 2.(km/d) for all cows each week
Cow1/6-1/12
1/12-1/19
1/19'1/26
- 1/26- 2/2
■ 2/2- 2/8
2/8-2/16
2/16-2/20
2/20-2/26
2019 1.2 -' 3.4 3.5 1.7 3.1 4.6 3.42043 5.2 4.2 4.1 4.9 2.7 3.4 4.1 7.62052 - 2.6 1.8 1.8 - 1.9 1.6 1.82063 - 3.8 2.5 3.2 - 2.2 2.9 2.32065 3.7 5.6 4.0 - 4.3 5.3 4.0 5.62069 2.1 . 3.0 4.5 3.6 2.3 4.3 3.7 5.72084 3.1 3.6 3.4 3.8 3.3 5.9 3.1 3.12085 4.3 5.0 6.2 - 4.2 3.6 3.9 4.42099 4.0 3.7 4.3 3.7 4.2 4.1 4.5 5.52119 1.7 4.6 3.0 2.4 3.4 4.0 3.3 1.52138 5.2 3.8 4.7 4.1 - 5.5 5.1 8.02177 8.4 5.7 - ■ 3.7 1.9 3.6 3.5 4.42179 3.8 5.6 4.1 3.9 5.2 5.5 - 5.32209 6.0 6.1 4.1 3.7 1.5 5.8 4.5 6.12241 3.8 3.1 3.0 3.7 2.3. 1.5 2.1 2.32248 .3.4 3.0 3.1 3.2 2.5 2.9 2.4 4.3Mean 4.0 4.2 3.7 3.5 3.1 3.9 3.6 4.5
SE 1.8 1.1 1.0 .73 1.1 1.4 .96 1.9
