ADAPTIVE RUMEN FUNCTION IN ELK (CERVUS-ELAPHUS-NELSONI) AND MULE DEER (ODOCOILEUS-HEMIONUS-HEMIONUS)

We tested the hypothesis that rumen function is adaptive to diet quality and intake rate using ruminally fistulated elk and mule deer. In experiment 1 we measured rumen particle-size distribution, rumen fill, and particle and liquid passage rates of animals fed three diets varying in quality (chopped pea, alfalfa, and wheat hays). In experiment 2, similar measurements were obtained on elk fed alfalfa hay ad libitum or at restricted intake levels. Rumen characteristics and passage rates of particles and liquids were similar for animals consuming alfalfa and pea hays. Intake, rumen dry-matter concentration and fill, and liquid passage rate were significantly lower when animals consumed wheat hay. Few significant differences in rumen characteristics or passage rates were found between animals fed alfalfa ad libitum or at restricted levels. Rumen liquid volume and dry-matter fill were related linearly to intake (r2 = 0.98 for both) in deer and elk fed alfalfa and pea hays. However, liquid volume and dry-matter fill of elk fed wheat hay and alfalfa at restricted levels were higher than the deer-elk interspecific regression, indicating an adaptive ruminal response. We concluded that rumen function was adaptive to both diet quality and availability, but that the response likely was subject to the limitations imposed by food characteristics and the inherent limitations of rumen structure and function.