Gonadotrophin-induced follicle development in red deer hinds during the breeding and non-breeding seasons

The effect of exogenous equine chorionic gonadotrophin (eCG) and endogenous (GnRH-treatment) gonadotrophins in promoting antral follicle development i n red deer hinds was assessed during the breeding and non-breeding seasons. After progesterone pretreatment, hinds received no further treatment, a si ngle injection of 300 iu equine chorionic gonadotrophin or infusion of GnRH (1.0 mug h(-1)) for up to 4 days. Ovaries were recovered (n = 5 per group) at the time of, or 36 h after, progesterone removal. All follicles greater than or equal to 2.0 mm in diameter were dissected out, their health statu s assessed and follicular fluid oestradiol content measured. Granulosa cell s were counted and their capacity for oestradiol and cAMP production assess ed in vitro. Oestrus, the preovulatory LH surge and ovulation rates were mo nitored in additional groups of hinds that had been treated identically (n = 5 per group). During the breeding season, all monitored animals ovulated, but five of 15 (one eCG, three GnRH, one progesterone alone) did not exhib it oestrus, and three (all eCG) had luteinized follicles. During seasonal a noestrus, four hinds (all eCG-treated) displayed oestrus, but only two ovul ated. Two non-ovulating hinds (one eCG, one progesterone alone) had luteini zed follicles. The total number of follicles, or of large (greater than or equal to 4 mm) follicles, did not differ significantly between seasons. The re were proportionately more healthy follicles during seasonal anoestrus (P <0.05). Treatment with GnRH, and-to a lesser extent eCG, increased the numb er of oestrogenic follicles and their follicular fluid oestradiol content. in summary, exogenous and endogenous gonadotrophins affected antral follicl e development similarly in both the breeding and nonbreeding seasons, altho ugh the response was variable among animals and often associated with failu re of oestrous expression, ovulation and with follicle luteinization.