Effects of subcutaneous melatonin implants on reproductive seasonality of farmed fallow deer (Dama dama)

Abstract

A total of 18 fallow does, including pubertal, non-pregnant and pregnant adult does (6 per class), each received a single subcutaneous implant containing 18 mg melatonin on 4 occasions at 29-30-day intervals from 10 November 1986 (~120-day treatment period). A further 18 contemporary does served as herd-mate controls. Two adult fallow bucks were treated the same and were run with the does until 16 March. Thereafer, 1 of 4 control bucks was run with the does until 1 June. Of the 6 pregnant does receiving implants within the last 40 days of their gestation, 4 failed to lactate after parturition in December 1986. The remaining 2 does successfully reared their fawns, as did the 6 contemporary controls. Mean (± s.e.m.) dates of first oestrus in 1987 were 27.6 February (± 3.0 days) and 22.9 April (± 0.8 days) for all treated and all control does respectively (P < 0.001). Pubertal does were generally later to exhibit first oestrus than were older does within their respective treatment groups. Return oestrus occurred only in 2 pubertal does (1 treated and 1 control) with remaining does conceiving to their first oestrus, as verified by plasma progesterone profiles. However, 5 (28%) of the treated does and 3 (17%) of the control does failed to maintain pregnancy and fawn in 1987. The mean (± s.e.m.) 1987 fawning date of the remaining does was 22.4 October (± 2.7 days) for the treated group (N = 13) and 13.1 December (± 0.8 days) for the control group (N = 15; P < 0.001). Mean (± s.e.m.) gestation length of treated does (238.9 ± 0.6 days) was significantly longer than that of control does (234.5 ± 0.4 days; P < 0.001). Of 13 fawns born to treated does, 4 (31%) died within 24 h of birth (mainly due to hypothermia) whereas all 15 fawns born to control does survived to weaning. Melatonin-treated bucks exhibited a marked advancement of neck muscle hypertrophy during the treatment period and displayed normal rutting activity (e.g. vocalization) in response to early oestrus in the treated does.