EFFECT OF SUBCUTANEOUS MELATONIN IMPLANTS ON THE SEASONAL ATTAINMENT OF PUBERTY IN FEMALE RED DEER (CERVUS-ELAPHUS)

The objective of this trial was to investigate the efficacy of strategically timed melatonin (Regulin) implantation in advancing the seasonal incidence of oestrus, ovulation, conception and parturition of pubertal red deer hinds. In September 1987, 37 prepubertal hinds were allocated to one of four treatment groups (n = 9, 10, 9, 9), balanced for liveweight. Group 1 hinds and a stag each received two Regulin implants on six occasions (28- and 30-day intervals) from 2 October (100 days after the winter solstice; 180-day treatment period); Group 2 hinds and a stag received the same treatment on five occasions from 17 November (140 days after solstice; 150-day treatment period); Group 3 hinds and a stag received the same treatment on four occasions from 30 December (180 days after solstice; 120-day treatment period) and Group 4 hinds and a stag received no treatments. In summary, treatment initiation was staggered by 40-day intervals but final implantation dates were similar (± 10 days). Groups remained separated until cessation of oestrous activity in control hinds (May 1988). Double melatonin implants elevated daytime plasma melatonin concentrations in hinds to physiological levels (≥ 100 pg/ml) for periods of at least 30 days. Evidence of pubertal oestrus/ovulation was observed for 31 (84%) hinds, 29 of which conceived and maintained pregnancy to term. All but one hind in each of Groups 1, 2 and 3 conceived and calved but only five (56%) control hinds exhibited pubertal oestrus/ovulation and only four of these hinds conceived and calved. Melatonin treatment significantly advanced the seasonal occurrence of puberty relative to control hinds. The mean dates of first oestrus, conception and parturition were advanced by 54, 50 and 48 days respectively in Group 1 hinds; 46, 41 and 38 days respectively in Group 2 hinds; and 22, 22 and 20 days respectively in Group 3 hinds. The interval between the initiation of treatment and the mean date of first oestrus was 147, 109 and 90 days for Groups 1, 2 and 3 respectively. Melatonin treatment did not affect liveweight gains of hinds between 9 and 12 months of age but subsequent reductions in liveweight gain occurred around the period of pubertal oestrus, being earlier for treated than control hinds. Mean liveweights at calving were similar between groups. It is concluded that melatonin (Regulin) implants are a practical and effective means for advancing the first calving season for red deer hinds. © 1990.