Summary. Eighteen ovariectomized fallow deer does and two adult bucks were used to investigate the effect of exogenous progesterone and oestradiol benzoate on oestrous behaviour and secretion of luteinizing hormone (LH). In Expts 1 and 2, conducted during the breeding season (April–September), does were treated with intravaginal Controlled Internal Drug Release (CIDR) devices (0·3 g progesterone per device) for 12 days and differing doses of oestradiol benzoate administered 24 h after removal of the CIDR device. The dose had a significant effect on the proportion of does that exhibited oestrus within the breeding season (P < 0·001), the incidence of oestrus being 100% with 1·0, 0·1 and 0·05 mg, 42% for 0·01 mg and 0% for 0·002 mg oestradiol benzoate. There was a significant log–linear effect of dose on the log duration of oestrus, which was 6–20, 2–14, 2–12 and 2 h after treatment with 1, 0·1, 0·05 and 0·01 mg of oestradiol benzoate, respectively. Dose had a significant effect on the peak plasma LH concentration (P < 0·01), mean (±s.e.m.) surge peaks of 27·7 ± 2·3, 25·9 ± 1·8 and 18·6 ± 3·4 ng/ml being observed following treatment with 1, 0·1 and 0·01 mg oestradiol benzoate respectively. In Expt 3, also conducted during the breeding season, progesterone treatment (0 vs. 6–12 days) before the administration of 0·05mg oestradiol benzoate had a significant effect on the incidence of oestrus (0/6 vs. 10/12, P < 0·05), but not on LH secretion. The duration of progesterone treatment (6 vs. 12 days) had no effect on oestrus. In Expt 4, conducted in the nonbreeding season (October–March), control does were largely unresponsive to treatment with 0·1 mg oestradiol benzoate. This was manifest in a lower proportion of does exhibiting oestrous behaviour and LH surges. Melatonin treatment, with implants administered on four occasions at intervals of 28–30 days starting from 24 October, significantly increased the proportion of does that exhibited oestrus in February, during the later phase of the nonbreeding season (7/8 vs. 1/8, P < 0·05). Melatonin-treated does also exhibited significantly higher basal plasma LH concentrations after removal of CIDR devices in February (5·8 ± 0·5 vs. 2·1 ± 0·4 ng/ml, P < 0·01). While only one control doe had an LH surge, with a peak of 13·8 ng/ml, all melatonin-treated does exhibited LH surges, with a mean peak concentration of 58·0 ± 8·4 ng/ml.
Keywords: fallow deer; progesterone; oestradiol benzoate; oestrus; luteinizing hormone