Abstract
Two experiments were conducted to determine the effect of feeding level or genetic background (Yorkshire and Poland China gilts and their reciprocal crosses) on the growth and atresia of new follicles following cautery of follicles present in the late luteal phase of the estrous cycle. Differences in ovulation rate before follicular cautery were found to be related to follicular growth following cautery. Yorkshire gilts had a higher ovulation rate and more follicles 3 to 6 mm in diameter, but a smaller diameter of the four largest follicles than the Poland China gilts. The greater ovulation rate in the crossbred gilts was not statistically significant, but the crossbred gilts had more follicles than the purebred gilts. Feeding level had no significant effect on ovulation rate or follicular development. Cautery of follicles on day-14 or -16 of the estrous cycle delayed the onset of estrus,decreased the number of atretic and normal follicles, but increased the frequency of follicles ≥11 mm in diameter. Yorkshire gilts were affected more than Poland China gilts by follicular cautery as evidenced by interactions for the number of normal and atretic follicles and the number of follicles 7 to 10 mm in diameter. Genetic group differences apparently are expressed in the rate of follicular development as well as number of follicles. A hypothetical model of follicular growth in swine has been proposed. The follicles destined to ovulate begin their development around day-5 of the estrous cycle and were estimated to require 15.6 days for development. The fate of follicles is determined by the particular endocrine status of the animal when the follicles attain specified steps in development. Copyright © 1976. American Society of Animal Science . Copyright 1976 by American Society of Animal Science.