Rumen-reticulum organ mass and rumen mucosa surface area of white-tailed deer (Odocoileus virginianus) consuming two diets
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Ungulate diets display spatial and temporal variation. To accommodate dietary variation, elasticity, organ mass, and absorptive capacity presumably change in the rumen-reticulum. The gastrointestinal organs, where most of the capacity and where most digestion occurs. I measured rumen-reticulum organ mass and absorptive capacity in white-tailed deer (Odocoileus virginianus) collected at Kerr Wildlife Management Area, Texas. I hypothesized that nutrient poor diets would result in greater mass-specific food intake because of low nutrient concentrations. The consequence would be heavy rumen- reticulum organs and low absorptive capacity. Since weaning, deer were fed a pelleted diet, ad libitum, of 1.77 or 2.67 kcal/gm digestible energy. In December 2017, 4.5- and 5.5-year-old deer were euthanized, the rumen-reticulum was extracted, thoroughly rinsed, wrung out, and weighted. Four, 1 x 3 cm samples were cut from four regions of the rumen. The samples were fixed in ExCell plus™ for 24 hours, then preserved in 70% ethanol until measured. For each 1 cm2 sample, I measured length and width of 10 randomly selected papillae, counted papillae density, and calculated a surface enlargement factor (SEF). My surrogate of food intake was first molar height measured on the right side of the jaw. Diet consumed by deer was unbeknownst to the measurer. Analyses of general linear models indicated that deer consuming the low energy diet had higher food intake, heavier rumen-reticulum organs, and lower SEF than deer consuming the higher energy diet. White-tailed deer adjust rumen-reticulum morphology to maintain digestive functions when diets vary in energy content.