Two experiments were conducted to investigate the effects of added fat in late gestation cow and heifer diets on thermogenic and neonatal metabolic responses. In Experiment 1, the effects of source of fat in late gestation diets on serum glucose and thermogenic response during short-term cold stress were examined in fall-born neonatal beef calves. Pregnant fall-calving heifers (n = 15) were randomly assigned to three dietary treatments: Control (CON, n=5), Safflower seed (SAF, n=5), or Cottonseed (COT, n=5) supplement. Hay-based isonitrogenous and isocaloric diets met NRC requirements while containing 1.53%, 4.0% and 5.0% fat for CON, SAF and COT diets, respectively. Diets were fed for 47.5 ( 5.4 d before calving. Heifers were weighed weekly and at parturition. At parturition, colostrum samples were taken from the dam, calves weighed, and vigor scores recorded. Calves remained with their dams for 5 h to nurse. At 5.5 h of age, calves were fitted with an indwelling jugular catheter. At 6.5 h of age, calves were placed in a 5(C cold room for 90 min. Shivering scores (1= no shivering, 2 = slight shivering 3 = muscle shivering, 4 = severe muscle shivering), rectal temperatures and blood samples were taken every 15 min. Colostrum samples were analyzed for fat, solids, protein, lactose and IgG concentrations. BW and BCS of heifers at calving, and birth weights and vigor scores of calves were unaffected by diet (P > .5). Mean fat, lactose and IgG concentrations in colostrum were not different (P > .3) among treatments. SAF tended to increase colostral solids (P = .11) and protein (P = .13) compared to COT or CON. During cold stress, calf body temperature increased in a quadratic fashion (P < .03). Mean glucose levels tended (P = .12) to be greater and shivering scores were non-significantly increased in CON compared to SAF or COT calves. Glucose concentrations averaged 74.4, 51.9, and 60.0 ( 7.3 mg/dl, whereas shivering score averaged 2.14, 1.69, and 1.68 ( .24 in CON, SAF and COT calves,
respectively. Shivering scores increased in all groups during cold exposure in a linear fashion (P < .001). Vigor scores increased in a linear fashion throughout cold exposure for all groups (P < .04). Cortisol concentrations decreased in a cubic fashion throughout cold exposure for all groups (P < .02). Cortisol concentrations averaged 28.62, 37.7, and 35.65 + 3.58 ng/ml in CON, SAF and COT calves, respectively. We conclude that calves from dams fed high fat diets containing safflower seeds or cottonseed respond similarly to cold stress, but these responses are not necessarily consistent with greater cold resistance.
In Experiment two, pregnant spring-calving cows (n = 75) were randomly assigned to two dietary treatments: Control (CON, n=35) and Cottonseed (COT, n=40). Hay-based isonitrogenous and isocaloric diets met NRC requirements while containing 2.0% and 5.0% fat for CON and COT diets, respectively. Diets were fed for 60 ( 5 d before calving. At parturition, calves were weighed, ambient temperature was recorded and dystocia score was recorded. At 30 min of age, rectal temperature one was recorded and shivering scores (1= no shivering, 2 = slight shivering 3 = muscle shivering, 4 = severe muscle shivering) were recorded. At 180 min postpartum, two blood samples were drawn from each calf to determine blood glucose and cortisol concentrations. At 36 + 4 h postpartum, two blood samples were again drawn from each calf to determine blood glucose and IgG concentrations. Calf birth weight, calf sex, vigor score, shivering score, time to stand, dystocia score, and serum IgG concentrations were unaffected (P > .5) by diet. Shivering score was affected by ambient temperature (P < .003) and time of calving (P < .006). Calf birth weights were unaffected by diet, calf sex, and the diet x calf sex interaction (P > .2). Mean time to nurse was non-significantly longer (101.2 vs 70.1 min), respectively, for COT calves compared to CON calves. At 30 min (P < .05) rectal temperatures were higher in male than female calves from dams on the COT diet (39.3 vs 39.1(C). Whereas rectal temperatures were lower in male calves than female calves from dams on the CON diet (39.1 vs 39.3(C; diet x calf/sex, P < .05). The same relationship among rectal temperatures was observed at 180 min (diet x calf/sex, P < .05). Changes in body temperature between 30 and 180 min were affected by diet (P < .05) as body temperatures for COT calves increased more from 30 min to 180 min than CON calves. Body temperature at 30 min was affected by time of calving (P < .01). Body temperature at 180 min was affected by ambient temperature at calving (P < .03) and there was a tendency for body temperature at 180 min to be affected by time of calving (P < .09). Serum glucose concentrations at time 180 min were unaffected by diet (P > .3). Serum glucose concentrations at time 36 + 4 h tended to be affected by sex (P < .07). With glucose levels higher in females (127 mg/dl) than in males (119 mg/dl). Differences in serum glucose at time 180 min and 36 + 4 h were not affected by diet, sex, or diet x sex interaction (P > .7). Serum glucose at 36 + 4 h was affected by ambient temperature at calving (P < .04). Mean serum cortisol concentrations tended to be higher (47.4 ng/ml vs 36.5 ng/ml) for COT calves compared to CON calves (P < .09). Differences in serum cortisol levels were unaffected by sex or diet x sex interaction (P > .5). When ambient temperature or time of calving were included as covariates, calf weight, calf vigor and serum IgG were unaffected by ambient temperature or time of calving (P > .05).