Advancement of reproductive activity, seasonal reduction in prolactin secretion and seasonal pelage changes in pubertal red deer hinds (Cervus elaphus) subjected to artificially shortened daily photoperiod or daily melatonin treatments.

Prepubertal red deer hinds were subjected to shortened daily photoperiod (8 h light per day, N = 3) or a daily (afternoon) melatonin injection (N = 4) for 83 days starting on 8 January, 2 weeks after the summer solstice. Compared with control hinds (N = 3) these treatments caused premature moulting of summer pelage, reduced serum prolactin concentrations to barely detectable levels about 34 days earlier than usual and advanced the date of mating. Calves were born earlier (P less than 0.005) in the hinds exposed to a shortened photoperiod (12 November +/- 1.7 days) and melatonin treatment (11 November +/- 3.2 days) than in control hinds (13 December +/- 7.9 days). Serum progesterone levels recorded before the first detected oestrus indicated that silent ovulations had occurred in many of the hinds (6 of 10) in this experiment. This study demonstrated the role of shortened daily photoperiod in red deer and indicated that the effects of reduced photoperiod observed were mediated by melatonin.