Growth and Replacement of the Bovine Ovarian Follicles during the Estrous Cycle1

Publisher Website
Google Scholar
Abstract
The morphology and the fate of ovarian follicles were studied at different stages of the estrous cycle. Four groups of 10 heifers were laparatomized on day 3, 8, 13 or 18 of an estrous cycle; the numbers of large (>6 mm), medium-sized (3 to 6 mm) and small (1 to 3 mm) follicles were recorded. In one-half of the animals, the largest (F1) and the second largest (F2) follicles on each ovary were marked, while in the remaining animals, all follicles larger than 5 mm were destroyed. Animals were autopsied 5 days later. Small follicles decreased in number gradually from day 3 to 18, while medium-sized follicles were more numerous on day 13 than at other stages. This was also observed in ovaries in which large follicles had been destroyed. The F1 follicles present on each ovary on day 3 were slightly larger on day 8, and 80% of these follicles were still the largest on the ovary at the end of this 5-day period. However, the F1 follicles seen on day 8 were smaller on day 13, and only 50% were still the largest. The F1 follicles observed on day 13 were much smaller on day 18, and only 10% were still the largest. There was also a rapid turnover of the F1 follicles after day 18, since F1 follicles ovulated only when ovulation occurred within 3 days after the day of marking. Replacement of the majority of the F2 follicles occurred at all stages. Five days after destruction of the follicles larger than 5 mm, the newly formed F1follicles were (1) smaller than the F1 follicles present in intact ovaries, if destruction had occurred on day 3 or 8, but (2) similar in size to the F1 follicles in intact ovaries, if destruction had occurred on day 13 or 18. Occurrence of estrus was not delayed by the destruction of the large follicles on day 18. These results indicate that follicular growth and replacement of the large follicle is more rapid at the end than at the beginning of the cycle and that important growth of the medium-sised, follicles occurs only when the largest follicle is either rapidly turning over or had been destroyed. Copyright © 1981. American Society of Animal Science . Copyright 1981 by American Society of Animal Science.

This publication has 0 references indexed in Scilit: