Follicular development in prepubertal heifers

Abstract

Ovarian follicular waves, characterized by the emergence, persistence, and regression or ovulation of a large follicle, occur in both cyclic and pregnant cattle. The purpose of this study was to characterize follicular activity and, in particular, the turnover of the large follicles in prepubertal heifers. The ovaries of six Santa Gertrudis heifers were monitored by ultrasound every other day for 28 days. The numbers of small (5 mm or less), medium (6–10 mm), and large (greater than 10 mm) follicles present at each session were determined, and the growth and regression of the largest follicle present on either ovary was characterized. Heifers were bled biweekly for 40 weeks to determine progesterone (P 4) concentrations. The prepubertal status of animals during the 28 day period of ultrasonic monitoring was confirmed by the absence of detectable luteal tissue, by ultrasonic evaluation and by P 4 concentrations of less than 1 ng ml −1. Heifers exhibited 3.3 ± 0.5 ( χ ± SEM) different largest follicles during the 28 day period with turnover occurring every 7.2 ± 0.9 days. The maximum diameter of the largest follicles ( n = 20) was 11.2 ± 0.4 mm. There were 4.5 ± 0.3 small, 2.1 ± 0.2 medium, and 0.6 ± 0.1 large follicles present per heifer per session ( P < 0.05). This study confirms that antral follicles of all sizes are present on the ovaries of prepubertal heifers, and is the first to demonstrate that large follicles grown and regress in a wave-like pattern during this physiological state.