Case Study: Effects of body weight gain and bovine somatotropin treatment of postpartum beef cows on concentrations of IGF-1, insulin, and glucose in blood plasma; luteal activity; and calf growth1

Angus × Hereford cows (2 and 3 yr of age, n = 37) were used to evaluate the effects of postpartum BW gain and treatment with bovine somatotropin (bST) on concentrations of IGF-I, glucose, and insulin in plasma during early lactation; luteal activity; and calf growth. Cows (456 ± 52 kg, BCS = 4.6 ± 0.4) were stratified based on calving date and BCS and randomly assigned to a 2 × 2 × 2 factorial: weight gain ≤0.4 kg/d (MWG) or >0.4 kg/d (HWG) during 24 to 59 d postpartum, injection with bST or saline (CON) on d 31 and 45 postpartum, and 2 or 3 yr of age. Concentrations of IGF-I in plasma before bST treatment were greater (P = 0.02) for HWG compared with MWG cows, and IGF-I was greater (P < 0.01) after bST in HWG bST cows compared with MWG bST, MWG CON, or HWG CON cows. Concentrations of glucose in plasma were greater (P ≤ 0.01) in HWG bST cows compared with HWG CON, MWG CON, and MWG bST cows after bST treatment. Weight gain and treatment with bST did not influence the percentage of cows with luteal activity by 59 d after calving. Average daily gain of calves to 140 d of age was greater (P < 0.01) for HWG-treated and tended to be greater (P = 0.06) for bST-treated cows compared with MWG and CON cows, respectively. Weight gain of young lactating beef cows increased plasma concentrations of IGF-I and glucose after treatment with bST.