Variation in antral follicle development during the follicular phase of the oestrous cycle in red deer (Cervus elaphus) hinds

The aim of this study was to quantify antral follicle populations in cyclic red deer hinds and to monitor follicle development leading to ovulation. O estrus was synchronized with exogenous progesterone and ovaries were recove red approximately 0, 12, 24 or 36 h (follicular phase) or 10 days (luteal p hase) after progesterone withdrawal (n = 5 per group). All follicles greate r than or equal to 2 mm in diameter were dissected out, health status was a ssessed, follicular fluid oestradiol content was measured, granulosa cells were harvested and their capacity for oestradiol and cAMP production was de termined. The time of oestrus and the preovulatory LH surge were monitored in five control hinds. Deer ovaries contained 26.6 +/- 3.45 (mean +/- SEM) follicles greater than or equal to 2 mm in diameter (range 4-81), with at l east one large antral follicle (diameter: 8.3 +/- 0.38 mm) per hind. There was a strong correlation between follicle size and granulosa cell populatio n (r(2) = 0.676). Approximately half (50.7%) of the follicles were classifi ed as healthy, with the percentage classified as atretic decreasing with in creasing follicle size. Neither the total number of antral follicles nor th eir size distribution differed significantly among groups. There were signi ficantly more (P < 0.05) healthy follicles at 24 h after progesterone withd rawal than at Oh, when large oestrogenic follicles had fewer granulosa cell s, lower follicular fluid oestradiol concentrations and lower aromatase act ivity (P < 0.05) than did those from other groups. In summary, antral folli cle development in red deer is similar to that in other monovulatory rumina nts, and at least one large follicle is present at all stages of the oestro us cycle.