Induction of early rutting in male red deer (Cervus elaphus) by melatonin and its dependence on LHRH

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Abstract
Eight red deer stags, 2 control, 3 control-immunized (i.e., a low titer of LHRH antibodies after active immunization 2 yr earlier) and 3 superior cervical ganglionectomized, were given a s.c. implant of melatonin in May at the nadir of the sexual cycle; 5 other stags remained untreated. All the melatonin-treated animals shed the velvet-like skin from the antlers in June or July at least 1 mo. before the untreated controls and had an early increase in blood plasma testosterone concentrations. The treated stags were also precocious in the development of rutting behavior, although this inductive effect was blocked dramatically in the control-immunized stags after a booster immunization against LHRH; these animals failed to show any further reproductive development and cast their antlers. Continuous exposure to melatonin in early summer will induce premature seasonal testicular development, an effect dependent on the secretion of LHRH and similar to that produced by exposure to short daylengths.