Manipulating melatonin in red deer (Cervus elaphus): Differences in the response to food restriction and lactation on the timing of the breeding season and prolactin-dependent pelage changes

In this study, we investigated the influence of food availability and lactation upon seasonality in red deer. This was examined by testing the hypothesis that advancing the timing of breeding and autumn moult using the hormone melatonin will be prevented when the food availability of lactating hinds is severely restricted. This hypothesis was rejected. Implanting 1 g of melatonin between June 22 and November 30 resulted in advances in the timing of the onset of ovarian activity and winter coat growth of 18 and 35 days, respectively. Whilst the onset of ovarian activity was unaffected by lactation and restricted food availability, these factors significantly delayed the winter coat growth by 20 days. The date of onset of winter primary fibre growth was negatively correlated to plasma concentrations of the hormone prolactin in July. We suggest that seasonal changes in the growth of primary hair fibres are modified by two mechanisms: the increasing duration of melatonin secretion, as day lengths decline, which depresses prolactin secretion, and low nutrition, which elevates prolactin secretion in lactating deer. To conclude, we have demonstrated that the sensitivity of red deer to photoperiodic influences is preserved in lactating animals at low levels of nutrition, and that the timing of the onset of the breeding season and winter coat growth differ detectably in their sensitivity to nutrition and lactation. © 1995 Wiley‐Liss, Inc.