Comparative Digestion of Grass in Mule Deer and Elk

Nutrient intake and utilization are fundamental processes linking wild ruminants to their food supply. Adaptations in body size, digestive physiology, and metabolic requirements influence the food niches and habitat requirements of these animals (Hoffman 1973, Kay et al. 1980, Hanley 1982). Studies of trophic relations and digestive morphology of wild ungulates suggest that larger ruminants are more efficient than smaller ones in digesting fibrous forages (Bell 1970, Prins and Geelen 1971, Short et al. 1974, Giesecke and Van Gylswyk 1975, Jarman and Sinclair 1979, Demment and Van Soest 1981, Mould and Robbins 1982). Few controlled feeding experiments have been conducted on wild ruminants to test this hypothesis (Arman and Hopcraft 1975, Mould and Robbins 1982). Although mule deer (Odocoileus hemionus hemionus) and elk (Cervus elaphus nelsoni) have both been categorized as mixed feeders (Kay et al. 1980:741, Hobbs et al. 1983), studies of their diet selection and digestive morphology suggest they may utilize foods differently (Short et al. 1965, Church and Hines 1978, Mould and Robbins 1982, Hobbs et al. 1983). We compared the digestive capability of a large ruminant (elk) and a small ruminant (mule deer) consuming grass hay and related these digestibilities to those predicted from in vitro measurements.