MANIPULATION OF REPRODUCTIVE SEASONALITY OF FARMED RED DEER (CERVUS-ELAPHUS) AND FALLOW DEER (DAMA-DAMA) BY STRATEGIC ADMINISTRATION OF EXOGENOUS MELATONIN

There is often a poor synchrony between the high energy demands of lactation in summer and the peak of pasture production and quality occurring in spring for red deer (Cervus elaphus) and fallow deer (Dama dama) farmed under pastoral conditions in temperate climates. Considerable research within the last decade has investigated either daily administration or constant infusion of exogenous melatonin in order to advance the breeding season and hence the seasonal pattern of births of farmed deer and, therefore, align lactation and feed production. Melatonin is the hormone involved in the transduction of photoperiodic information to the endocrine system leading to precise timing of reproduction. Owing to the absence of pregnancy and lactation, the pubertal hind/doe provides the simplest model for exogenously controlling the seasonality of oestrus, ovulation and conception. All forms of exogenous melatonin delivery initiated in summer (10-12 months of age) are effective in advancing the onset of puberty. However, the degree of advancement relative to control females has been highly variable, reflecting a wide range of treatment protocols. The most significant variables appear to be the time of onset of treatment and the degree of social interaction between treated and control animals. Initiation of treatments less than 100 days after the winter solstice are likely to delay puberty by impinging upon a possible photoperiod entrainment period. Initiation of treatments more than 100 days after the solstice advances puberty, with progressively later initiation dates generally resulting in smaller degrees of advancement. Melatonin-treated red deer hinds and stags appear to influence the timing of puberty of contiguous control hinds. The maximum degree of puberty advancement so far achieved by melatonin treatment has been 54 days for red deer and 56 days for fallow deer. In adult female deer, lactation does not appear to markedly influence the degree of phase shifting by melatonin treatment. However, because melatonin treatment initiated before the end of pregnancy, 140-170 days after the winter solstice, may prevent lactogenesis, the use of melatonin is contra-indicated during pregnancy. Treatment initiation after the onset of lactation does not appear to influence milk yields, as evidenced by calf/fawn growth rates. Treatment of adult male red and fallow deer during summer advances all aspects of reproductive seasonality. Coincident treatment of males and females appears to result in coincident early rutting and oestrous activity, leading to high conception rates. Long-term consequences of treatment of red deer stags include early sexual quiescence and occasional expression of transient testicular cycles, with re-synchronisation of treated and control stags occurring 14-15 months after the initiation of treatment. However, initiation of treatment of red deer stags less than 50 days after the winter solstice delays sexual quiescence and sexual recrudescence, indicating that increasing photoperiod in early spring is important in the entrainment process. While seasonal birth/lactation patterns for red and fallow deer can be advanced by exogenous melatonin treatment, research is needed to elucidate the actual effects on overall productivity, particularly in relation to calf/fawn growth rates and the impact of precocious puberty in early-born animals.