Effect of feeding melatonin to red deer (Cervus elaphus) on the onset of the breeding season.

Four non-lactating red deer hinds kept in natural light were each given orally 5 mg melatonin daily in the afternoon from 1 June to 5 October. The time difference between melatonin administration and sunset was 5.5-6 until the end of August, thereafter gradually decreasing to 3.5 h. Onset of oestrous cyclicity occurred in late August and early September, 2-8 weeks in advance of control hinds. A stag given 10 mg melatonin daily shed the antler velvet on 18 July, 4 weeks earlier than untreated stags, and started rutting behaviour in July-August, 2 months before the usual time.