Costs of lactation to body condition and future reproduction of free-ranging mule deer Odocoileus hemionus (Cervidae)

We compared indices of nutritional condition and size between lactating and dry ≥2.5-year-old mule deer Odocoileus hemionus from three free-ranging populations in the Southwestern USA to quantify the energetic costs of lactation on endogenous energy reserves, determine whether differences persisted over winter, and assess carryover effects on future reproduction. In autumn, dry and lactating females differed in 77% of comparisons of condition and 20% of comparisons of size among population-years. In all significant comparisons, dry females were in better condition than lactating, and were smaller. Accrual of fat reserves was affected by lactation more than were protein reserves or size, but of those variables in which dry females differed from lactating in autumn, differences were lost by spring in 100% of cases. Accrual of some indices of condition was negatively affected by consecutive years of full lactations, but this effect was small compared to the overall magnitude of the lactation effect. Neither pregnancy, litter size, birth mass, nor survival of fawns to 30 days or to weaning were affected by previous successful reproduction, while birth date showed a weak positive effect. Likely because of convergence in condition overwinter, the negative influence of lactation on condition did not have a significant carryover effect on future reproduction. Because our study populations experienced moderate to severe nutritional stress, lack of a carryover effect is likely valid for most mule deer populations.