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J. Anim. Sci. 2003. 81:885-894
© 2003 American Society of Animal Science

Effects of feeding supplemental fat to beef cows on cold tolerance in newborn calves1

R. E. Dietz*, J. B. Hall2,*, W. D. Whittier{dagger}, F. Elvinger{dagger} and D. E. Eversole*

* Department of Animal and Poultry Sciences and and {dagger} Virginia-Maryland College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg 24061

2 Correspondence:
Dept. of Animal and Poultry Sciences, 302 Litton Reaves (phone: 540-231-9153; fax: 540-231-3713; E-mail:
jbhall{at}vt.edu).


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 Implications
 Literature Cited
 
Our objectives were to examine the effects of added fat in late-gestation cow diets on neonatal response to cold. In Exp. 1, pregnant fall-calving heifers received control (n = 5), safflower seed (n = 5), or whole cottonseed (n = 5) diets. The hay-based, isonitrogenous, and isocaloric diets, fed for 47 d prepartum, contained 1.5, 4.0, and 5.0% fat for control, safflower, and whole cottonseed diets, respectively. At calving, calf BW and vigor score, as well as fat, lactose, and IgG in colostrum were not affected (P > 0.30) by diet. Heifers fed the safflower diet tended to have greater colostral solids (P < 0.10) than heifers fed the control or whole cottonseed diets. At 6.5 h of age, calves were placed in a 5°C cold room for 90 min. Calf vigor, shivering, body temperature, and blood samples were taken every 15 min. During cold stress, calf body temperature decreased 0.7°C (P < 0.03). Across all diets, shivering and serum glucose concentrations increased (P < 0.05), whereas calf vigor and cortisol concentrations decreased (P < 0.02) during cold exposure. In Exp. 2, pregnant spring-calving cows (n = 98) received a control (n = 47) or whole cottonseed (n = 51) supplement. Hay-based diets fed for 68 d prepartum contained 2.0 and 5.0% fat for control and whole cottonseed diets, respectively. Calf BW, vigor, shivering, dystocia score, time to stand, time to nurse, serum glucose concentrations, and serum IgG were not affected (P > 0.50) by diet. Between 30 and 180 min, body temperature of calves from dams fed the whole cottonseed supplement decreased (P < 0.05) more than calves from dams fed the control supplement. Serum glucose concentrations in calves were not affected by diet (P > 0.30). Serum cortisol concentrations tended (P < 0.09) to be greater for calves from dams fed whole cottonseed than control calves. When ambient temperature was <= 6°C, calves born to dams fed whole cottonseed had greater (P < 0.05) BW, tended (P < 0.1) to stand earlier, and had greater serum IgG concentrations. We conclude that calves from dams fed high-fat diets containing safflower or whole cottonseed respond similarly to cold stress, but these responses may not be consistent with greater cold resistance. In addition, high-fat dietary supplementation of late-gestation cows may only be beneficial during calving seasons with prolonged cold weather.

Key Words: Calves • Fats • Nutrition • Prepartum Period • Survival


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 Implications
 Literature Cited
 
Losses of calves during the early neonatal period have a negative impact on the economic sustainability of the cow/calf operation. Azzam et al. (1993) estimated that approximately 95,000 calves die annually during the neonatal period due to cold stress. These losses result in an estimated $38 million reduction in income for cow/calf operations. Therefore, increasing cold tolerance in the newborn calf is essential.

Prepartum nutrition may alter a neonate’s thermogenic ability and resistance to environmental stress. Prepartum nutritional restriction of dams adversely affected calf birth weight, survivability (Corah et al., 1975; Warrington et al., 1988), and thermogenic ability of neonatal ruminants (Alexander 1962; Carstens et al., 1987). In contrast, dams fed a high-fat diet prepartum produced calves with greater resistance to cold stress (Lammoglia et al., 1999a). Animals fed diets rich in polyunsaturated fatty acids had increased brown adipose tissue activity, thermogenesis, and cold resistance (Nedergaard et al., 1983; Lammoglia et al., 1999a), and the quantity of essential fatty acids in the diet appeared to be important.

In Southern and mid-Atlantic states, whole cottonseeds are a readily available, moderately priced, high-fat byproduct. However, whole cottonseeds contain approximately 28% less linoleic acid than safflower seeds. We hypothesize that there is no difference between safflower seed and whole cottonseed as a fat supplement, but information on the influence of prepartum supplementation of whole cottonseed on physiological responses and calf survival in response to cold stress is limited.

The objectives of this study were 1) to compare the source of prepartum energy on calf physiological responses to cold stress, and 2) to investigate the effect of high-fat diets on neonatal calf responses in a moderately cold climate.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 Implications
 Literature Cited
 
Two trials were conducted, a cold chamber experiment during the fall of 1999 and a field trial during the spring of 2000. The Virginia Tech Animal Care and Use Committee approved all procedures.

Experiment 1
Experiment 1 was designed as a preliminary experiment to ascertain if there was a significant difference between prepartum diets containing safflower seed or whole cottonseed on neonatal calf response to cold stress. Fifteen fall-calving pregnant Angus and Hereford heifers (initial BW = 573.3 ± 18.2 kg) were randomly assigned to one of three dietary treatments. Cows and calves were housed at the Virginia Tech Beef Cattle Center in Blacksburg (37°17' N; 80°24'W). All three diets (Table 1Go) were fed as total mixed diets. Heifers received either 1) a control diet (control; n = 5) containing 1.5% crude fat, 2) a safflower-supplemented diet (safflower; n = 5) containing 4.0% crude fat, or 3) a cottonseed diet (whole cottonseed; n = 5) that contained 5.0% crude dietary fat. Approximately 50 to 60% of the safflower seeds were cracked during mixing and handling. Gestating heifers were fed their respective diets for 47.5 ± 5.4 d before expected parturition and continued to receive that diet until parturition. Diets were formulated to meet NRC requirements for gestating heifers (NRC, 1996) as well as to be isoenergetic and isonitrogenous. Animals in each treatment were offered the same amount of DM each day. Heifers were group fed within their treatments, and total feed offered corresponded to the number of heifers still pregnant. Each day, for all treatment groups, rejected feed was weighed and recorded to determine the precise amount of feed consumed. Overall DMI per heifer was not different among treatments (data not shown). Diet ingredients and total mixed rations were analyzed for DM, CP, ether extract, and ADF using AOAC methods (AOAC, 1990). Total digestible nutrients were estimated from ADF values. All diets were supplemented with free-choice trace mineral salt, and all animals had ad libitum access to water.


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  		Table 1. Diet composition for Exp. 1
 
Heifers calved over a 68-d period from late August until early November. Most heifers calved within the first 30-d of the experiment. However, two control heifers had to be removed from the experiment for reasons not related to experimental procedures. Replacement control heifers were Charolais, and calved later, but data from these heifers were not different from other control animals, and were included in statistical analysis. Replacement control heifers received the prepartum diet for 40 and 43 d, respectively.

Heifers were observed for signs of parturition every 2 h and were observed continuously once parturition started. Within 1 h after calving, the cow/calf pair was removed from the treatment group and placed in a maternity pen that was maintained at ambient temperature. Colostrum samples were taken from the dam and stored at -20°C until assayed for IgG concentrations, milk fat, protein, lactose, and solids. Calves were weighed and then returned to their dams and allowed to suckle. The calf remained with its dam for approximately 5 h. At 5.5 h of age (birth = 0) and 60 min before cold exposure, an indwelling catheter (Angiocath; 20 gauge x 11 cm; Sierra, Tiffin, OH) was inserted into the jugular vein of each calf using aseptic procedures, and a 46-cm catheter extension was attached.

At 6.0 h of age, calves were removed from their dams, and moved 2.6 km by truck to a 5°C cold room for 90 min. Individual calves were placed in the single cold room at 6.5 h of age with one calf in the cold room at each time. All fluid had evaporated, and the calves were dry when placed in the cold room. Rectal temperatures (mercury thermometer; Jorvet, New Hyde Park, NY), vigor scores, shivering scores, and 10-mL blood samples were taken at 0, 15, 30, 45, 60, 75, and 90 min while the calf was restrained in a metabolism crate within the cold room. Blood collection tubes contained NaF to inhibit glucose metabolism. Vigor scores for calves during cold exposure were 1 = alert, vigorous, active; 2 = alert, calm, able to stand; 3 = not alert, quiet, lethargic, unable to stand. Shivering scores for calves during cold exposure were 1 = no shivering; 2 = slight localized shivering; 3 = moderate body shivering; 4 = severe overall body shivering. A thermostatically controlled refrigeration unit and air circulation fan cooled the room. Calves were protected from air currents generated by the fan by a canvas partition. Temperature variations during the experimental period were less than 3°C. Oxytetracycline (LA-200, Pfizer, Exton, PA) was administered to each calf at the end of the sampling period as directed by a veterinarian. Calves were then returned to the Virginia Tech Beef Cattle Center, and placed with their dams.

Blood was allowed to clot on ice for 1 h, and a serum separation filter (Auto-Iso-filter, Becton, Dickenson Co., Franklin, NJ) was inserted in each tube. Tubes were placed in a centrifuge at 1,700 x g for 20 min to yield serum, which was stored at -20°C until glucose and cortisol concentrations were determined. Serum cortisol (kit TKC05; DPC, Los Angeles, CA) concentrations were determined using a RIA procedure (Laredo, 1994). Spectrophotometric techniques were used to determine serum glucose concentrations (kit 315; Sigma, St. Louis, MO). Composition of colostrum was determined by the regional Dairy Herd Improvement Association Laboratory, Blacksburg, VA, using the Milko Scan instrument (Foss, Hillerod, Denmark) following the procedures of Soriano et al. (2000). Colostrum samples were diluted 1:2 with distilled water when necessary for analysis. Colostrum IgG (Bovine Vet Rid kit; Bethyl, Montgomery, TX) concentrations were determined using radial immuno-diffusion procedure (Besser and Gay, 1994). Intraassay coefficients of variation were 3.4 and 5.0% for glucose, and cortisol assays, respectively. Intra and inter-assay coefficients of variation for the IgG assay were 2.0 and 3.5%, respectively.

Experiment 2
Experiment 2 was designed to test the effects of normal- or high-fat (whole cottonseed) prepartum diets on calf survivability and physiological responses under production conditions. Ninety-eight spring calving mature cows (initial BW = 635.9 ± 6.7 kg; BCS = 6.0 ± 0.01) blocked by calving date, and housed at the Bland County Correctional Facility, Bland, VA (37°13'N; 81°12'W) were randomly assigned to one of two treatment groups. Cows received either a control diet (Table 2Go) consisting of hay, whole corn, and soybean meal that contained 2% crude dietary fat (n = 47; control) or a high-fat diet consisting of hay, whole corn, and whole cottonseed that contained 5% crude dietary fat (n = 51; whole cottonseed). Gestating cows were group-fed their respective diets 68.4 ± 1.5 d before the expected date of first parturition and continued to receive that diet until parturition. Diet ingredients were analyzed for DM, CP, ether extract, and ADF using AOAC methods (AOAC, 1990). Total digestible nutrients were estimated from ADF. Diets were formulated to be isonitrogenous and isocaloric and to meet NRC requirements for gestating cows (Table 2Go; NRC, 1996). Animals had ad libitum access to water and a complete mineral mix.


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  		Table 2. Diet composition for Exp. 2
 
Seventy-five calves (whole cottonseed, n = 40; control, n = 35), born during a 12-d period in March, were used for measures of early neonatal health and performance. Ambient temperature, precipitation, time of calving (i.e., hour of day), calf weight, and dystocia scores were recorded at parturition. At 30 min postpartum, rectal temperature (mercury thermometer; Jorvet) was measured and calf vigor score and calf shivering score were recorded. The amount of time required for calves to stand and nurse, and the precipitation and daily high and low temperatures at the calving location were recorded. Average ambient temperature during the calving period was approximately 11°C.

At 180 min postpartum, two 10-mL blood samples were drawn via jugular venipuncture and rectal temperature was measured from each calf. At 36 ± 0.5 h postpartum (hereafter denoted as 36 h), two 10-mL blood samples were again drawn from the calves. At each time, one sample was placed in blood collection tubes containing NaF to prevent glucose metabolism by red blood cells. Blood collection tubes containing no additives were used for determination of cortisol at 180 min postpartum and IgG concentrations at 36 h postpartum. Blood was allowed to clot on ice for 1 to 2 h, a serum separation filter (Auto-Iso-filter, Becton, Dickenson Co.) was inserted in each tube, and then centrifuged at 1,700 x g for 20 min to yield serum, which was stored at -20°C until glucose, cortisol, and IgG concentrations were determined using procedures indicated in Experiment 1. Intraassay and interassay variations were less than 5% for all assays.

Statistical Analysis
In Experiment 1, calf birth weights and heifer colostrum composition were analyzed by ANOVA using GLM procedures of SAS (SAS Inst., Inc., Cary, NC). Calf body temperature, shivering score, vigor score, serum glucose, and serum cortisol data were analyzed by ANOVA as repeated measures using the GLM procedures of SAS. Orthogonal polynomial contrasts were used to analyze time effects. The full model included diet, calf sex, time, and their interactions. Effect of calf sex and calf sex x time interaction were not significant (P > 0.1) and were removed from the final model. As calves were individually exposed to cold stress, the experimental unit was calf. The reduced model included main effects of diet, time, and their interaction with calf (diet x time) as the error term.

In Experiment 2, calf birth weight, minutes to stand, minutes to nurse, serum cortisol concentration, serum IgG concentration, and ambient temperature were analyzed by ANOVA using the GLM procedures of SAS. The model included main effects of diet, calf sex, and their interactions. Calf body temperature at 30 and 180 min, and serum glucose concentration at 180 min and 36 h were analyzed by ANOVA as repeated measures using the GLM procedures of SAS. Since each calf was born at a unique time and under unique environmental conditions, the experimental unit was calf. The model included diet, calf sex, time, and their interactions. Data were analyzed using ambient temperature at time of calving and time of calving as covariates. When a covariate or interaction among main effects was not significant, the most appropriate reduced model was used. Relationships between ambient temperature and shivering score or ambient temperature and time to nurse were analyzed by PROC REG of SAS. Shivering, vigor, and cow dystocia scores were analyzed by {chi}2 using the CAT MOD procedures of SAS.

To determine the effects of prepartum diet on calves born during cold temperatures, a subset of data was compiled from calves born when calving temperatures were below 6°C. Data from these calves (n = 19) were subjected to the same statistical procedures as described above except that diet was the only independent variable included in the model.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 Implications
 Literature Cited
 
Experiment 1
The fall-calving heifers delivered 10 heifer and 5 bull calves. The ratios of male to female calves were 2:3, 2:3, and 1:4 for control, safflower, and whole cottonseed fed heifers, respectively. One control heifer and one heifer fed the safflower diet required minimal calving assistance, and calving ease score was 1.2 ± 0.1 for all treatments. Calf birth weights and mean vigor score at birth were not affected (P > 0.5) by diet, calf sex, or the diet x calf sex interaction (data not shown). Mean fat, lactose, and IgG concentrations in colostrum were not different (P > 0.3) among treatments. However, heifers fed the safflower supplement tended to have greater colostral solids (P < 0.1), but not protein (P < 0.13), than those fed whole cottonseed or control diets (Table 3Go).


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  		Table 3. Effect of prepartum diet on calf weights, calf vigor, and colostral constituents (mean ± SE) at calving (Exp. 1)
 
Body temperature of calves for all treatments decreased throughout cold exposure resulting in a 0.7°C drop in body temperature (P < 0.03). Calf body temperature changed during cold exposure in a quadratic fashion due to a slight increase in body temperature at 75 min of cold exposure in all groups (Figure 1Go). Dietary treatment did not alter body temperature response to cold stress. Shivering score averaged 2.1, 1.7, and 1.7 ± 0.2 in calves from dams fed control, safflower, and whole cottonseed diets, respectively. During cold stress, calves in all treatment groups had a linear increase in shivering score (P < 0.001, Figure 2Go). Similarly, vigor score of calves in all groups increased in a linear fashion throughout cold exposure (P < 0.01, Figure 3Go). However, dietary treatment did not alter vigor score or shivering score response to cold stress.



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  		Figure 1. Changes in body temperature during cold stress of 6.5-h-old calves born to dams fed control, 2% crude fat ({diamondsuit}); safflower, 4% crude fat (•); or whole cottonseed, 5% crude fat ({blacktriangleup}) diets prepartum in Exp. 1. Pooled SE = 0.11. No effect of diet (P = 0.80); quadratic effect of time (P < 0.030).

 


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  		Figure 2. Changes in shivering score (1 = none to 4 = severe) during cold stress in 6.5-h-old calves born to dams fed control, 2% crude fat ({diamondsuit}); safflower, 4% crude fat (•); or whole cottonseed, 5% crude fat ({blacktriangleup}) diets prepartum in Exp. 1. Pooled SE = 0.31. No effect of diet (P > 0.30); linear effect of time (P < 0.001).

 


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  		Figure 3. Changes in calf vigor score (1 = vigorous to 3 = lethargic unable to stand) during cold stress in 6.5-h-old calves born to dams fed control, 2% crude fat ({diamondsuit}); safflower, 4% crude fat (•); or whole cottonseed, 5% crude fat ({blacktriangleup}) diets prepartum in Exp. 1. Pooled SE = 0.16. No effect of diet (P > 0.30); linear effect of time (P < 0.04).

 
Mean serum glucose concentrations in calves from control dams averaged 22.5 and 14.4 mg/100mL greater than calves from dams fed safflower, and whole cottonseed diets, respectively, throughout the cold exposure period. However, mean glucose concentrations were similar among treatments (P < 0.12; Figure 4Go). Mean glucose concentrations in calves born to dams fed control, safflower, and whole cottonseed diets averaged 74.4, 51.9, and 60.0 ± 7.3 mg/100mL, respectively. In addition, mean glucose concentrations increased for all calves in all treatments throughout cold exposure (P < 0.001).



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  		Figure 4. Changes in serum glucose concentrations during cold stress in 6.5-h-old calves born to dams fed control, 2% crude fat ({diamondsuit}); safflower, 4% crude fat (•); or whole cottonseed, 5% crude fat ({blacktriangleup}) diets prepartum in Exp. 1. Pooled SE = 7.3. Effect of diet (P < 0.12); linear effect of time (P < 0.001).

 
Serum cortisol concentrations in calves were not affected by diet (P > 0.7). However, cortisol concentrations were affected by time of cold exposure for all groups (P < 0.02). Serum cortisol concentrations decreased in a cubic fashion throughout cold exposure (Figure 5Go). Cortisol concentrations averaged 28.6, 37.7, and 35.6 ± 3.6 ng/mL for calves from dams fed control, safflower, and whole cottonseed diets, respectively. In general, cortisol concentrations were elevated when the calf was initially placed in the cold room, followed by a continuous decrease in concentrations throughout 90 min of cold exposure.



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  		Figure 5. Changes in circulating cortisol concentrations during cold stress in 6.5-h-old calves born to dams fed control, 2% crude fat ({diamondsuit}); safflower, 4% crude fat (•); or whole cottonseed, 5% crude ({blacktriangleup}) fat diets prepartum in Exp. 1. Pooled SE = 5.9. No effect of diet (P > 0.70); cubic effect of time (P < 0.02).

 
Experiment 2
Calf Responses Complete Data Set.
When all observed births were included in the analysis, prepartum dietary treatment had limited impact on the variables measured. Means of metabolic, immunologic, and physiologic traits for calves from dams fed cottonseed and control diets are summarized in Table 4Go. At birth, calf birth weight, vigor score, shivering score, time to stand, and dystocia score (Table 4Go) were not affected by diet (P > 0.5). Calf birth weights were also not affected (P > 0.2) by calf sex or diet x calf sex interaction (data not shown). Mean time to nurse was not different (P > 0.2) for calves from dams fed whole cottonseed or control diets with average time to nurse of 81.9 ± 10.7, and 67.5 ± 11.8 min, respectively.


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  		Table 4. Least squares means (± SE) of metabolic, immunological, and physiological traits for calves born to cows fed cottonseed or control supplements in Exp. 2
 
Ambient temperature at birth was a significant covariate for shivering score and time to nurse. Shivering score decreased as ambient temperature increased (P < 0.003) and when calves were born during warmer periods of the day (P < 0.006). Low ambient temperatures also prolonged (P < 0.02) time to nurse. However, calf weight, calf vigor, and time to stand were not altered by ambient temperature or time of calving (P > 0.05).

Body temperature at 30 and 180 min were not affected (P > 0.13; Table 4Go) by diet or calf sex. However, the change in body temperature from 30 to 180 min was altered by prepartum diet (P < 0.05) since body temperatures of calves from cows fed the whole cottonseed supplement decreased slightly, whereas body temperatures of calves born to cows fed the control supplement increased. A diet x calf sex interaction was observed at 180 min (P < 0.05). Rectal temperatures were higher in male than female calves from dams fed the whole cottonseed diet (39.2 ± 0.2 vs. 38.9 ± 0.2°C), whereas rectal temperature was lower in male than female calves from dams fed the control diet (38.9 ± 0.2 vs. 39.3 ± 0.2°C).

Body temperature at 30 min was affected by time of calving (P < 0.01). In contrast, body temperature at 180 min was affected by ambient temperature at calving (P < 0.03) with only a tendency to be affected by time of calving (P < 0.09).

Prepartum dietary treatment did not (P > 0.2) influence serum glucose concentrations in calves at 180 min and 36 h or serum IgG levels at 36 h (Table 4Go). Serum glucose at 36 h increased (P < 0.04) as ambient temperature at calving increased (r = 0.29). Changes in serum glucose between 180 min and 36 h were not affected by diet, sex, or diet x sex interaction (P > 0.7). However, serum glucose concentrations increased (P < 0.001) by almost twofold from 180 min to 36 h in both treatments.

Mean serum cortisol concentrations tended to be greater (P < 0.09) in calves born to cows fed the whole cottonseed diet than calves from cows fed the control diet (47.4 ± 4.3 vs. 36.5 ± 4.6 ng/mL). Differences in serum cortisol concentrations were not affected by sex or diet x sex interaction (P > 0.5).

Calf Responses, Low Ambient Temperature Data Set.
To examine possible effects of prepartum diet on calves that were born during cold temperatures, a subset of data from 19 calves (whole cottonseed, n = 12; control diet, n = 7) born when ambient temperatures were below 6°C was analyzed. This subset was chosen to include calves born below the lower critical temperature for newborn calves. Similar to the complete data set, prepartum dietary fat levels did not affect a majority of the variables examined. However, calves from dams fed the whole cottonseed supplement were heavier (P < 0.04) at birth than calves from dams fed the control supplement (Table 5Go). Calves from dams fed the whole cottonseed supplement tended to stand sooner (P < 0.07), had improved vigor (P < 0.06), and had greater (P < 0.10) serum IgG concentrations at 36 h. There was a tendency (P = 0.11) for prepartum diet to influence the change in body temperature from 30 to 180 min postpartum. Body temperature decreased 0.4°C in calves from dams fed whole cottonseed, whereas body temperature increased 0.2°C in calves born to cows fed control diets (-0.4 ± 0.2 vs. 0.2 ± 0.3; P < 0.1).


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  		Table 5. Effect of prepartum diet on physical characteristics and serum immunoglobulin concentration of calves born when ambient temperatures were < 6°C
 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
Implications
 Literature Cited
 
Feeding increased levels of fat to cows during the last 60 d of gestation did not dramatically alter calves’ responses to induced cold stress or the actual calving environment compared to calves from dams fed lower fat diets. Physiological and metabolic indicators were influenced by duration of cold stress or ambient temperatures at calving rather than prepartum diet.

The linoleic acid and/or unsaturated fat content of the prepartum diet may be an important factor influencing calf survival, and subsequent cow reproduction (Bellows, 1999). Rats fed diets containing high amounts of PUFA had greater concentrations of uncoupling protein 1, a protein important for thermogenesis in brown adipose tissue, than rats fed a diet low in PUFA (Nedergaard et al., 1983). In addition, n-3 fatty acids appear to be more potent stimulators of production of messenger RNA (mRNA) for uncoupling protein 1 than n-6 fatty acids (Clarke, 2000; Takahasi and Ide, 2000). In contrast, rats fed high-fat diets had increased concentrations of mRNA for uncoupling proteins irrespective of the degree of saturation of dietary fatty acids (Takahashi and Ide, 1999). Also, reproductive response of cows to prepartum fat supplement was similar among different fat sources or oilseeds (Bader et al., 2000; Graham et al., 2001). Experiments designed to examine the precise amount or type of PUFA needed to maximize brown adipose tissue thermogenesis in ruminants and calf or lamb survival may be warranted.

Because the amounts of linoleic acid needed to increase calf survival and cold resistance are still unknown, we felt it was necessary to test the hypothesis that feeding prepartum diets supplying 5% fat from whole cottonseed (56.3% linoleic acid) or safflower seed (79.1% linoleic acid) would not differ in calf response to cold stress. In Exp. 1, we were unable to detect significant differences in calf response to a controlled cold stress between animals from dams fed safflower or cottonseed diets. As designed, the diets were to provide 0.7, 2.0, and 2.6% linoleic acid for control, whole cottonseed, and safflower diets, respectively. The reduced percentage of fat in the safflower diet, as indicated by ether extract analysis, may have resulted in total linoleic acid content for the safflower and whole cottonseed diets being similar. In addition, the hay portion of the diet may have supplied significant amounts of 18:2n-6 and 18:3n-3 PUFA (Loor et al., 2002), resulting in PUFA exceeding 3.0% of the diet in both high-fat diets.

Therefore, whole cottonseed based diets may provide sufficient amounts of linoleic acid to mimic the effects of safflower seed. Alternatively, low animal numbers may have limited our ability to detect subtle differences between the safflower- and the cottonseed-supplemented diets. Based on the lack of dramatic differences in calf response between the two oilseeds, we proceeded with the field trial using whole cottonseed as the fat source.

Calf birth weights in both studies were not affected by diet. In contrast, feeding a high-fat diet increased birth weights of calves born when temperatures were below 6°C. Lammoglia et al. (1999b) reported increased birth weights in calves from dams that received a high-fat diet during the last 53 d of gestation than calves from dams fed a normal (<2.0%) fat diet. In addition to dietary effects, cold exposure of pregnant dams can increase (Symonds et al., 1992; Colburn et al., 1996) or decrease (Andreoli et al., 1988) subsequent birth weight of neonatal ruminants. Birth weights were increased compared to calves from control cows only in the 12 calves from cows fed whole cottonseed that were born when temperatures were below 6°C. Since all cows were exposed to the same prepartum environment, the cause of only a few calves from whole cottonseed fed dams having higher birth weights is not apparent. However, the present results agree with findings reported by Lammoglia et al. (1999a), who suggested that effects of high-fat diets on birth weight are not consistent. Together, these studies suggest that birth weight of the calf is a function of total dietary energy intake rather than source of calories; however, differential partitioning of nutrients into specific tissues such as brown adipose tissue may occur.

Calves did not exhibit an initial increase in rectal temperature in response to cold stress as previously reported (Lammoglia et al., 1999a, b). In addition, increasing fat in the prepartum diet did not slow the cold stress-induced decline in rectal temperature in the present study. Calves in Exp. 1 were born in the fall of the year, which may have altered their thermogenic response. Exposure of dams to cold conditions during late gestation increased brown adipose tissue stores and thermogenic rates in newborn lambs (Stott and Slee, 1985; Symonds et al., 1992). In contrast, although spring-born calves had larger stores of brown adipose tissue than fall-born calves, peak metabolic rates were not affected by season of birth (Martin et al., 1999). Increasing dietary fat prepartum enhanced cold resistance in spring-born, but not fall-born, calves (Lammoglia et al., 1999b). Lammoglia et al. (1999b) suggested that environmental conditions during the late prepartum period may influence response to fat supplementation. These studies suggest that season of birth may not alter thermogenic response to short-term cold stress, but may provide spring-born calves with greater brown adipose tissue reserves to withstand prolonged cold stress. The mechanism for seasonal differences in response to cold stress by prepartum fat-supplemented neonates warrants further study.

Contrary to other studies (Lammoglia et al., 1999a,b; Martin et al., 1999), we allowed calves to nurse ad libitum for 5 h before cold stress (Exp. 1) or continuous ad libitum nursing (Exp. 2). Whereas this method may have confounded our ability to detect differences in dietary effects on brown adipose tissue thermogenesis, it did allow us to examine the total impact of prepartum fat supplementation on the ability of the neonate to resist cold stress. It is possible that calves in the present study had more energy available from colostrum in the form of glucose, glycogen, or fats when they entered the cold room, which may account for the lack of increase in rectal temperature in response to initial cold stress. The transient rise in rectal temperature at 75 min coincided with increased shivering and plasma glucose concentrations. At this time, calves may have been mobilizing energy from brown adipose tissue and using shivering thermogenesis in an attempt to increase body temperature.

Although rectal temperatures in response to cold stress were not modified by prepartum diet, physiological responses indicated that calves were experiencing cold stress. Decreased calf rectal temperatures, depressed calf vigor, increased shivering, and increased glucose concentrations during the cold challenge are indicative of cold stress. The duration and magnitude of cold exposure should have been sufficient to detect different thermogenic responses by calves from the various prepartum diets. The 0.7°C reduction in calf body temperature observed in this study was similar in magnitude to body temperature declines observed in cold-stressed calves in other experiments (Vermorel et al., 1989; Lammoglia et al. 1999a,b). In addition, these researchers reported that dietary effects on rectal temperatures were readily apparent after 45 min of cold stress.

In contrast, environmental conditions in Exp. 2 may not have been sufficiently severe to challenge newborn calves. Hypothermia is a significant cause of mortality in neonatal calves (Bellows at al., 1987). Calf losses to hypothermia are greatly increased when ambient temperatures are below 0°C or precipitation exceeds 10 mm on the day of calving (Azzam et al., 1993). Although Exp. 2 was conducted during late winter, average environmental temperatures were warmer than expected for that time of year. Mean daily temperatures at the location of Exp. 2 for January, February, and March for the past 10 yr were 4.9, 3.3, and 6.6°C, respectively (National Weather Service, 2000). Average ambient temperatures at calving were 11.3° and 10.5°C for calves born to cows fed whole cottonseed or control supplements, respectively. Reported lower critical temperatures for newborn calves range from 9° to 22°C (Rowan, 1992). Therefore, the warm ambient temperatures, considerable daytime heating, and lack of any significant precipitation during the data collection period allowed for a relatively low-stress environment for calving.

Failure of high-fat diets to increase serum glucose concentrations was unexpected and is in contrast to other studies (Lammoglia et al., 1999a, b). Blood glucose concentrations play an important role in thermogenesis in the neonatal calf (Godfrey et al., 1991) supplying substrate for shivering thermogenesis. In the first experiment, chemical analysis indicated that the control diet contained an estimated 3% more TDN than the high-fat diets, which may explain the slight elevation in glucose concentrations in calves born to cows fed the control diet. Liver glycogen content was increased in lambs born to glucose-infused ewes (Clarke et al., 1996). Diet composition differences encountered were not planned since all diets were formulated to have similar DM, CP, and TDN. However, glucose concentrations increased during cold exposure indicating that calves, regardless of treatment, were mobilizing additional substrates essential for thermoregulation, which is consistent with changes in plasma glucose in the cold-stressed heifer (Andreoli et al., 1988), ewe (Symonds et al., 1988a), and calf (Lammoglia et al., 1999b). Since calves in Exp. 2 were born into relatively warm environmental conditions, glycogen stores may have provided sufficient glucose regardless of prepartum diet. Increased serum glucose concentrations in calves between 3 and 36 h postpartum are consistent with consumption of high concentrations of lactose and other gluconeogenic energy substrates via colostrum (Rauprich et al., 2000).

Elevated circulating cortisol concentrations are normally associated with short- and long-term stress, and slight elevations in cortisol concentrations were noted in acutely cold-stressed lambs and calves (Cabello, 1983; Lammoglia et al., 1999b). However, no elevation in cortisol levels was noted in long-term cold-stressed heifers and ewes (Andreoli et al., 1988; Symonds et al., 1988b). The transient rise in cortisol observed in acutely cold-stressed calves in the present study might have increased glucose concentrations as a result of gluconeogenesis. Perhaps the increased cortisol concentration was an adaptive mechanism to cold stress or maybe it was a response to absence of the dam or sampling procedures.

Alternatively, cortisol concentrations and body temperatures in all calves (Exp. 1) may have been increased due to transport stress at the time of placement into the cold chambers. Transportation to the cold chamber required approximately 10 min to complete, and the animals were restrained during this time. Transport stress and handling increases cortisol concentrations and heart rate in cattle (Grandin, 1997). Although it is difficult to compare actual values across experiments, body temperatures of calves at the initiation of cold stress in the present experiment were equivalent to the maximal temperature observed by Lammoglia et al. (1999a). If rectal temperatures and cortisol concentrations were elevated in response to transport stress, it may have interfered with our ability to detect differences among treatments.

High-fat diets decreased milk fat and protein in dairy cows (Wu et al., 1994; Bitman et al., 1996). In the present study, cows fed high-fat diets had a 1.5% decrease in milk fat percentage vs. cows fed the control diet. However, cows fed safflower seed supplement had greater concentrations of milk solids than cows fed the control diet. Feeding a high-energy diet prepartum increased IgG concentrations in colostrum and in neonatal calves (Odde, 1988), but in the present study, the high-fat diets did not influence colostral IgG concentrations. Calves that stood more rapidly after birth had increased serum IgG and IgM concentrations (Odde, 1988) than calves that were slow to stand. Since calf serum IgG concentrations are a function of both colostral IgG concentrations and volume of colostrum consumed, increased IgG levels in calves born during cold temperatures from cows fed the high-fat diets (Exp. 2) may indicate that these calves consumed more colostrum than calves from cows fed the control diet.


   Implications
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Implications
Literature Cited
 
Whole cottonseed seems to be an acceptable substitute for safflower seed in late-gestation beef cow diets. However, feeding dams a high-fat diet prepartum did not improve calf response to short-term cold stress or cool (10°C) ambient temperatures at calving. Feeding high-fat diets may improve resistance of neonatal calves to extremely cold calving conditions, but reduced time to standing and increased serum immunoglobulin concentrations were the only positive calf responses observed. Under mild spring calving conditions, feeding high-fat diets prepartum may have limited positive effects on neonatal calf survival; therefore, inclusion of high-fat supplements may be warranted only when feed costs are not increased.


   Footnotes
 
1 The authors appreciate the donation of whole cottonseed for this experiment by T. Auphin and the Commonwealth Gin, Windsor, VA. The assistance of the employees of the Virginia Tech Beef Center and the Virginia Department of Corrections with data collection and B. Caldwell with manuscript preparation was invaluable. Back

Received for publication May 8, 2002. Accepted for publication January 3, 2003.


   Literature Cited
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Implications
 Literature Cited
 


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