The Effect of Orally Administered Melatonin on the Seasonality of Deer Pelage Exchange, Antler Development, LH, FSH, Prolactin, Testosterone, T₃, T₄, Cortisol, and Alkaline Phosphatase

Five milligrams of melatonin (M) per day was administered orally to four male white‐tailed deer on a schedule that mimicked first decreasing and then increasing lengths of natural photoperiod. The following seasonal phenotypic and hormonal responses were observed: 1) Pelage exchange, antler mineralization, velvet shedding, and rutting behavior of experimental animals were advanced by 50–55 days. 2) Prolactin (PRL) levels exhibited a bimodal curve with peaks in May and August, as compared to a monomodal curve of controls (peak in June). 3) Peak FSH levels of M‐fed deer were advanced 2 months as compared to controls (June vs August). 4) LH concentrations of both groups reached maxima in July; however, in the experimental group, LH levels declined much faster than in controls and then rose again in October‐November. 5) Testosterone (T) concentrations of M‐fed bucks were elevated 2 months ahead of controls. 6) Melatonin treatment had no significant effect on seasonal variation of T₃, or T₄. 7) No seasonal rhythm of cortisol was seen in either group and no detectable effect of M was evident. 8) No statistical differences in levels of alkaline phosphatase were seen between groups, although concentrations in experimental bucks sharply dropped to basal levels two months ahead of controls.