EFFECTS OF SOMATOTROPIN ON THE CONCEPTUS, UTERUS, AND OVARY DURING MATERNAL RECOGNITION OF PREGNANCY IN CATTLE

Effects of recombinant bovine somatotropin (rbST) on ovarian and uteri ne function and the production of components of the insulin-like growt h factor (IGF) system were examined during the period of maternal reco gnition of pregnancy in cattle. Lactating dairy cows were treated with 25 mg/d rbST (n = 8) or saline (n = 8) for 16 d after estrus. Ovaries , uteri, and conceptuses were collected on Day 17 after estrus. The le ngth (millimeters) of the conceptus was recorded. The concentration of IGF-I and the content of IGF-binding proteins (BP) in uterine flushin gs were determined. Corpora lutea (CL) were weighed, and the number of follicles (greater than or equal to 2 mm in diameter) were counted. F ollicular fluid from the largest and second-largest follicles was assa yed for the concentration of IGF-I, IGFBP, progesterone, and estradiol . The length of the conceptus and the total amount of IGF-I in uterine fluid were similar for rbST and control. Recombinant bST increased 1) the weight of the CL, 2) the number of largest follicles (10 to 15 mm in diameter), 3) the concentration of IGF-I in the follicular fluid, 4) the follicular fluid content of IGFBP of the largest estrogenic fol licle, and 5) the quantity of IGFBP in uterine flushings. The concentr ation of progesterone in the follicular fluid tended to be increased i n rbST-treated cows, whereas the concentration of estradiol was simila r to that of control cows. The concentration of progesterone in plasma was similar for rbST compared with control. In conclusion, the admini stration of rbST in lactating dairy cows for 16 d after estrus did not alter the growth of the conceptus collected on Day 17. The greatest r esponses to rbST were found within the ovary, where rbST increased the weight of the CL and altered the amount of IGF-I and IGFBP in the fol licular fluid.