The energy cost of gestation in white-tailed deer

Gestation in white-tailed deer (Odocoileus virginianus) of northern regions occurs throughout winter, when forage quantity and quality are limited. Ou r objective was to measure the energy cost of gestation during winter and s pring in order to determine its impact on energy balance of deer. We used i ndirect respiration calorimetry to measure the metabolism of 21 pregnant de er every 2-4 weeks during gestation (January-May). Fasting metabolic rates (FMR) were used to develop a predictive equation to evaluate temporal energ y costs. A measurable increase in metabolism occurred on day 91 of gestatio n. FMR (kJ/kg body mass (BM)(0.75) per day) of pregnant deer rose curviline arly (FMR = 0.02(days)(2)-3.261(days) + 465.2), with 92.2% of the increase occurring in the third trimester; costs were 45% greater in the last trimes ter for pregnant than for nonpregnant deer. Peak FMR of pregnant deer at 20 0 days gestation was 617 kJ/kg BM0.75 per day, 84% above that of nonpregnan t deer (335 kJ/kg BM0.75 per day). The total energy cost of gestation, in t erms of FMR, was 78 004 kJ/kg BM0.75 per 200 days, a 16.4% increase above t hat of nonpregnant deer. The temporal increase in energy costs was correlat ed with spring green-up, indicating important relationships between energy demands, food quality and availability, spring weather, and physiological a daptations in deer.