Control of Food Intake in Domesticated Deer

Daylength controls changes in voluntary food intake (VFI) in seasonal breeds of deer. The control of VFI by daylength is mediated through hypothalamic, pituitary, and peripheral hormones much in the same way that daylength controls reproduction. Daylength drives the seasonal rhythm of VFI but exerts an entraining influence over a circannual rhythm through melatonin secretion. In two experiments described in the chapter, prolactin injections during short days increased VFI in deer but had no effect in sheep. Prolactin plays an important role in mediating the effects of seasonality in species that show this trait, such as reindeer and red deer; but not in species that have lost this trait, such as the domesticated sheep. Future research is required to demonstrate the neurohormonal control of changes in VFI in seasonal breeds of deer and to study the annual patterns of body growth, VFI, and digestion in tropical breeds of deer to establish whether these differ in deer that evolved at high latitudes.