Differential Loss of Fat and Protein by Mule Deer during Winter

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Abstract
Body composition of hand-reared mule deer (O. hemionus) was studied by use of tritiated water (HTO) over a 120-day period. Energy intake was controlled at different levels for 3 treatment groups. All treatment groups received submaintenance ratios to ensure catabolism of energy reserves. Changes in total body water indicated catabolism of both fat and protein reserves. High-intake animals lost less fat (38%) than either medium- (46%) or low- (67%) intake deer. High and medium groups lost similar amounts of protein (16% and 18%, respectively), whereas low-intake animals lost 31% of their body protein. Significant loss of protein occurred in all groups within the first 40 days. Fat reserves were depleted at similar rates among treatments. Rates of protein loss between high-and medium-intake groups were similar, but the low-intake group differed significantly. Analysis of the amount of energy contributed to the energy pool by catabolism of fat or protein suggested 3 phases of protein catabolism, similar to those observed in starvation studies with other mammals. Consequences of fat and protein catabolism in wintering mule deer are discussed.