Reproductive and endocrine changes in ewes actively immunized against estrogens and androgens

Twenty ewes were divided equally into two treatments to be actively immunized simultaneously against estrogen and androgen conjugated to ovalbumin (steroid immunized) or immunized against ovalbumin alone (control) to determine the effects of steroid immunization on reproduction and pituitary function. Ewes were immunized at week 0, 3 and 5 of the 93-week study and exposed to a fertile ram for two breeding seasons (weeks 7-25 and weeks 60-67). Steroid immunization reduced the proportion of ewes which exhibited estrus during the first breeding season when antibody activity against steroids was highest and reduced the proportion of ewes lambing after both breeding seasons. Ovulation rate, observed only during the second breeding season, was two times higher in steroid immunized ewes, but no increase in percent lamb crop per ewe lambing was observed. Pituitary concentrations of immunoactive LH (determined by radioimmunoassay), bioactive LH (determined by stimulation of mouse Leydig cell production of testosterone) and receptors for LHRH were increased by steroid immunization. These changes in pituitary LH resulted in a decreased ratio of bioactive to immunoactive LH observed in the pituitary and a decrease in circulating concentrations of bioactive LH. It was concluded from this study that simultaneous active immunization against estrogens and androgens increases ovulation; however, estrus and lambing rates may be reduced when antibody activity is high. Ovulation rates were increased despite the fact that no change in FSH was observed and the biopotency of LH was decreased in steroid immunized ewes.