ENERGY-INTAKE RELATIONSHIPS FOR WHITE-TAILED DEER ON WINTER BROWSE DIETS

Food intake by white-tailed deer (Odocoileus virginianus) is affected by digestibility, but this relationship has not been well quantified f or natural winter diets. We studied relationships between digestible e nergy (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 conte nt and 1 pelleted commercial diet to 9 captive fawns in 4 sets of dige stion 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 (k cal/kg(0.75)/day) were positively and linearly related to dietary DE ( r(2) = 0.75-0.82, P less than or equal to 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. 1 973), DEI of fawns in the present study was only 63% of maintenance. T he 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 w ould lose greater than or equal to 30% body mass. Therefore, more dige stible foods such as northern white cedar (Thuja occidentalis), lichen (Usnea spp.), and possibly litterfall (deciduous leaves and conifer s hoots) may be important winter forages.