Maintenance energy requirements, postpartum reproduction, and ruminal temperature at parturition and estrus of beef cows

Scope and Method of Study. Angus x Hereford cows were used to determine the effects of postpartum weight gain (WG) and treatment with bovine somatotropin (bST) on concentrations of hormones in plasma and calf growth. Cows were assigned to a 2 x 2 factorial: WG, to gain either ≤ 0.4 kg/d or > 0.40 kg/d until d 59 post partum. Cows were injected with bST (250 mg) or saline on d 31 and 45 after calving. Variation in maintenance energy requirement (MR) was determined in nonlactating, pregnant Angus x Hereford cows in feeding trials in each of 3 yr. Cows were classified based on MR as low (> 0.5 SD less than mean, L), moderate (+/- 0.5 SD of mean) or high (> 0.5 SD more than mean, H). Relationships among MR and calf performance, plasma concentrations of IGF-I, T4, glucose, insulin and ruminal temperature were determined in yr 2; description of the proteome and evaluation of protein abundance in Longissimus dorsi (LM) of cows with different MR were evaluated in yr 2 and 3; and the relationship of ruminal temperature with parturition and estrus was evaluated. Proteins from LM were separated separate by 2D-DIGE and abundance was quantified and compared. Rumen boluses were placed in the rumen of the cows to measure ruminal temperature (every 15 min) around parturition and estrus.;Findings and Conclusions. Weight gain influenced plasma concentrations of IGF-I and glucose after treatment of cows with bST. However, treatment did not influence reproduction of the cows. Weight gain and bST treatment of the dam increases calf growth. The greatest differences in MR within year for all cows ranged from 24 to 29%. Birth and weaning weights of calves, postpartum BW and BCS of cows, resumption of luteal activity, plasma concentrations of hormones, and ruminal temperature of cows were not influenced by MR. However, concentrations of IGF-I in plasma were negatively correlated with MR at 2 mo post partum. Protein abundance tended to be greater in H for cofilin-2 compared with L cows. Ruminal temperature decreased 1 d before parturition and increased during estrus. Increase efficiency in the cow-calf segment of the beef industry is feasible. These results, the novel description of the proteome of LM in beef cows and the protocol developed to separate the proteins, provide important information for future research. Weaning heavier calves using similar resources, or weaning similar weight calves using less feed, will improve efficiency of beef cattle production and enhance sustainability of the environment.