Use of rumen-reticulum fill to examine nutrient transfer and factors influencing food intake in white-tailed deer (Odocoileus virginianus)

Estimating relationships of gut fill in mammalian herbivores is useful to understanding digestive functions. Large animals might have more fluid in the gut to facilitate nutrient transfer between the gut lumen and the gut wall. Furthermore, relationships between concentrations of dietary refractory and indigestible fiber (CRIF) and gut fill might indicate whether chemostatic factors or physical distension of the gut affects food intake. We collected white-tailed deer (Odocoileus virginianus (Zimmermann, 1780); 122 males, 152 females) from three sites in central and south Texas that varied in diet quality as indexed by rumen-reticulum crude protein concentrations. Large animals did not have more fluid in their rumina-reticula than small animals because the scalar between body mass and wet mass of rumen-reticulum contents was not greater than the scalar estimated for dry mass of rumen-reticulum contents. We expected a positive or an inverse relationship when rates of forage comminution, digestion, and particle passage were high or low, respectively. At the site where deer had access to a high-quality pelleted diet, we detected a positive relationship between CRIF and dry mass. At sites with free-ranging deer and lower quality diets, relationships between CRIF and dry fill were inversely related. Food intake of deer was probably influenced by chemostatic factors at the site with a high-quality pelleted diet and by physical distension of the gut at the other two sites.