Ovarian antral follicular dynamics and serum progesterone concentration during the oestrous cycle of Bannur ewes

Abstract

Oestrus in 18 Bannur ewes was synchronized with cloprostenol, a PGF₂α analogue. Blood samples were collected from these ewes prior to cloprostenol injection, and on day 0, 6, 11 and 16 for determination of progesterone concentration, Six ewes each randomly chosen were slaughtered on days 6, 11 and 16 of the oestrous cycle and ovaries were collected to study antral follicular dynamics, The progesterone concentration was 3.83 0.21 nM/litre before cloprostenol injection, 0.49±0.04 nM/litre on day 0, 2.12±0.56 nM/litre on day 6, 5.97±0.21 nM/litre on day 11 and 1.57±0.39 nM/litre on day 16 of the oestrous cycle. The ovary showed 3 periods of antral follicular activity: period 1 on day 3 or 4 to day 8 of 9; period 2 on day 8 to day 13 or 14; and period 3 on day 10 to ovulation, The total population of the antral follicles and the population in different size groups i.e., 2-4 mm, 4-6 mm and >6 mm diameter, revealed that the corpus luteum exerted no paracrine effect but acted through humoral negative feedback to prevent maturation of the follicles.