Influence of nutrition and lactation on ovulation and conception in red deer

Reproduction incurs a high energetic cost and failure to meet nutritional needs results in reproductive failure. In red deer hinds, the interaction between nutrition, summer lactation and subsequent ovulation/conception is of particular interest for farmed deer production in NZ due to climatic constraints to summer pasture production in many areas. However, few studies have focussed on the potential perturbing effects of poor nutrition on lactational outputs and potential flow-on effects on ovulation/conception. As lacta tion in red deer naturally persists well beyond the autumn mating period, lactational anoestrus (through hormonal feedback mechanisms) is not a normal feature of the species reproduction. However, lactation is of high nutritional cost to the hind and can potentially exert considerable influence on the incidence and timing of conception via changes in hind liveweight, lipid depots and general body condition. Supporting evidence for this hypothesis is derived from studies of wild red deer within habitats marginal to species survival (e.g. Isle of Rhum, Scotland), where climatic variables greatly influence annual reproductive success of hinds. Under such conditions, even the differences in maternal investment (via lactation) required to raise male and female calves have been demonstrated to influence the subsequent success and timing of conceptions. Studies of farmed red deer in Scotland also demonstrated that hinds on different levels of pasture nutrition during lactation exhibited significant differences in conception date, with earlier conceptions favouring hinds on higher levels of nutrition. There is a growing body of evidence from monitoring of farmed red deer in New Zealand that the interaction between lactation and hind body condition score (BCS)/ liveweight influences subsequent conception rate and date. Recent studies on pre-rut versus post-rut calf weaning practices demonstrated effects of lactation on hind BCS and liveweight, calf growth rates and hind conception dates. These studies highlight the need to better understand the “costs” of lactation on reproductive performance, particularly under conditions of nutritional constraints.