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Endocrine Differences Associated with Follicular Development and Ovulation Rate in Swine Due to Breed and Energy Intake¹

University of Wisconsin,^,3 Madison

Abstract

Forty-five Chester White and 40 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 the 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. The 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 the proportion of mature follicles that were ovulated as an effect of feed or breed. Total follicular fluid weight was greater by 0.63 gm. in the high-energy than 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 in the anterior pituitary gland weight. The Poland China breed had higher unit concentrations of FSH and LH 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.

¹ Paper No. 855 from the Division of Genetics and No. 352 from the Department of Meat and Animal Science. Published with the approval of the Director of the Agricultural Experiment Station.

² The authors wish to express their appreciation to A. B. Chapman for advice on statistical methods and to R. H. Grummer for obtaining the experimental animals and supervising their care.

³ Department of Meat and Animal Science, Zoology and Genetics.