Endocrine Differences Associated with Follicular Development and Ovulation Rate in Swine Due to Breed and Energy Intake

Abstract

Poland China gilts were used to study physiological variations in ovulation rates, presumably brought about by variations in the amount of pituitary gonadotropins secreted and released, and by the ability of the ovaries to respond to gonadotropins. Experimentally, variations in ovulation rates were brought about by using animals on different energy intakes and of different breeds. Supplementing the basal ration with lard for approximately 14 days increased the potential ovulation rates significantly by 3.3 ova. Chester White gilts had a greater potential by 3.9 ova than Poland China gilts of the same sexual age. There appeared to be no difference in proportion of mature follicles that were ovulated as an effect of feed or breed. Total follicular fluid weight was greater by 0.63g in the high-energy and low-energy-fed gilts. Similarly, the Chester White gilts showed greater follicular development than Poland China gilts. Progesterone inhibition of follicular development was greater in the low-energy than high-energy-fed gilts. Follicular development in the Chester White and Poland China breeds was equal under progesterone inhibition, but the Chester Whites showed greater response to PMS than the Poland Chinas. The ration treatments to which the gilts were subjected failed to show any differences in unit concentrations of gonadotropins or in the anterior pituitary gland weight. The Poland China breed had higher unit concentrations of FSH (follicle stimulating hormone) and LH (luteinizing hormone) than the Chester White breed. The release of FSH and LH was at least partially inhibited by progesterone. The ratio of FSH to LH was wider in progesterone-injected than in estrous gilts.