Effects of Four Genetic Groups and Two Levels of Feeding on Ovulation Rate and Follicular Development in Puberal Gilts2

Ovulation rate, follicular development, anterior pituitary gland weight and corpora lutea weight were studied in a total of 74 puberal gilts of the Poland China and Yorkshire breeds and their reciprocal crosses. The effects of two levels of feeding also were studied for the first 16 days of the puberal estrous cycle in half of the gilts and for the puberal estrous cycle plus 3 days of the succeeding cycle in the other half of the gilts. The Yorkshire gilts exceeded the Poland China gilts in (1) ovulation rate (P<.01), (2) anterior pituitary gland weight (P<.01), (3) the number of small and medium follicles and the total number of follicles at day-16 (all P<.01) and (4) the number of small follicles and the total number of follicles at day-3 (both P<.01). At day-16 the Poland China gilts had heavier corpora lutea (P<.01) and more large follicles than the Yorkshire gilts (P<.01). Gilts on the high feeding level had a greater ovulation rate (P<.01) but had no significant difference in follicular development from those on the low feeding level. The act of mating had no significant effect on ovulation rate. There were more medium and total follicles at day-16 than at day-3 (both P<.01) with no significant difference in the number of small or large follicles.