Compensatory effect of the heat increment of feeding on thermoregulation costs of white-tailed deer fawns in winter

Abstract

For northern white-tailed deer (Odocoileus virginianus) fawns, the energetic cost of thermoregulation (H c E) during severe winters can result in substantial catabolism of body-tissue reserves. The heat increment of feeding (H i E) has the potential to offset thermoregulatory energy expenditure that would otherwise require the catabolism of these reserves. During winters 1996 and 1997, we conducted 18 fasting and 18 on-feed heat-production trials using indirect respiration calorimetry in a metabolic chamber. Nonlinear regression analysis was used to estimate the lower critical temperatures (T lc ) and determine the fasting metabolic rate (FMR) and resting metabolic rate (RMR). Resulting models were used to calculate H i E, H c E, and percent substitution of H i E for H c E. For fawns fed a natural browse diet, estimated FMR and RMR were 352 and 490 kJ·kg body mass (BM) -0.75 ·d -1 , respectively; this 40% increase in thermoneutral heat production reduced T lc from -0.8 to -11.2°C between the fasted and fed states, respectively, and reduced H c E by 59% for fed fawns. For fawns fed a concentrate diet, estimated FMR and RMR were 377 and 573 kJ·kg BM -0.75 ·d -1 , respectively. Level of browse intake had a significant effect on RMR andT lc . RMR was 12% higher for fawns on a high versus a low level of intake, and estimated T lc was -15.6 and -5.8°C, respectively. Our data indicate that the energetic cost of thermoregulation is probably a minor portion of the energy budget of a healthy fawn consuming natural forage.