Energy Intake Relationships for White-Tailed Deer on Winter Browse Diets

Abstract

Food intake by white-tailed deer (Odocoileus virginianus) is affected by digestibility, but this relationship has not been well quantified for natural winter diets. We studied relationships between digestible energy (DE) content of winter diets and intake of food and DE by white-tailed deer in Maine. We fed 8 winter browse diets varying in DE content and 1 pelleted commercial diet to 9 captive fawns in 4 sets of digestion trials. Digestible energy content of browse diets ranged from 1.95 to 2.39 kcal/g. Dry matter intake (g/kg 0.75 /day) and DE intake (kcal/kg 0.75 /day) were positively and linearly related to dietary DE (r 2 = 0.75-0.82, P ≤ 0.01). Daily DE intake (DEI) of browse diets by deer provided 30-88% of maintenance requirements. When dietary DE was 2.2 kcal/g, the reported minimum DE value at which deer can regulate intake at maintenance requirements (Ammann et al. 1973), DEI of fawns in the present study was only 63% of maintenance. The 2.2 kcal/g threshold, commonly considered a minimum requirement for dietary DE, appears inadequate for maintenance on winter browse diets. We estimated that fawns on diets composed of >70% hardwood browses would lose ≥30% body mass. Therefore, more digestible foods such as northern white cedar (Thuja occidentalis), lichen (Usnea spp.), and possibly litterfall (deciduous leaves and conifer shoots) may be important winter forages