Pregnancy and bovine somatotropin in nonlactating dairy cows: I. Ovarian, conceptus, and insulin-like growth factor system responses

Abstract

Nonlactating dairy cows were used to examine effects of bovine somatotropin (bST) on components of the insulin-like growth factor (IGF) system. Estrus was synchronized in cows with a Presynch + Ovsynch protocol and timed AI (TAI; n = 55) or not TAI (cycling, C; n = 23) on d 0 (time of synchronized ovulation). On d 0 and 11, cows received bST (500 mg) or no bST, and were sacrificed on d 17. Pregnancy rates were less in bST cows (27.2%, 9 of 33) than in controls (63.6%; 14 of 22). In contrast, conceptuses were larger in bST-treated cows (39.2 ± 4.8 cm) than in controls (20 ± 4.3 cm). Total interferon-τ in uterine luminal flushings (ULF) was greater in bST-treated cows (7.15 > 2.36 μg). Number of class 2 follicles (6 to 9 mm) was less in bST-C cows on d 7 and 16. On d 17, corpus luteum (CL) weight tended to be greater in bST-treated cows. Concentrations of progesterone were greater after d 10 in C than in pregnant (P) cows. In the ULF, IGF-binding protein-3 was greater in bST-P cows than in pregnant cows. A tendency for an increase in IGF-I hormone concentrations in the ULF was detected on d 17 in bST-treated and cyclic cows. Endometrial mRNA for IGF-I, IGF-II, IGFBP-2, and IGFBP-3 increased in bST-C, but not in bST-P cows. Treatment with bST increased plasma concentrations of insulin, IGF-I, and growth hormone (GH). In conclusion, bST may have hyperstimulated plasma IGF-I and insulin to cause asynchrony between conceptus and uterus that was detrimental to pregnancy.