DYNAMICS OF RUMEN-RETICULUM CAPACITY AND FILL IN FEMALE WHITE-TAILED DEER (ODOCOILEUS VIRGINIANUS)
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Understanding capacity and fill dynamics of the gastrointestinal tract under different environmental conditions gives insight into how herbivores meet life history demands. In female white-tailed deer (Odocoileus virginianus) rumen-reticulum capacity and fill presumably fluctuate with the demands of pregnancy and lactation. Other studies suggest rumen-reticulum capacity and fill decrease with higher quality diets (high crude protein-CP, low acid detergent fiber-ADF). Lower body conditions might warrant larger rumen-reticulum capacities to accommodate increased food intake. Rumen-reticulum capacity and fill might also be influenced by seasonal fluctuations in food intake associated with predictable change in forage abundance. We collected 72 adult female white-tailed deer in March, September, and November, 2009-2010, from Kerr Wildlife Management Area, Kerr County, Texas. From each animal we measured rumen-reticulum capacity and fill (wet and dry) as well as body weight, fetus weight, mandible length, rump fat, and dietary ADF and CP. We built models and used Akaike Information Criteria to select models to understand which hypotheses explain capacity and fill dynamics. Rumen-reticulum capacity fluctuated with reproductive state and dietary nutrition. Wet rumen-reticulum fill fluctuated with the animal’s body condition, dietary nutrition, and reproductive state. Dry rumen-reticulum fill fluctuated with the animal’s dietary nutrition. Pregnant deer had significantly smaller rumen-reticulum capacities but relatively constant amounts of fill. Deer with a lower body condition score had larger amounts of fluid in the rumen-reticulum. Greater amounts of CP were associated with higher proportions of dry weight fill within the rumen-reticulum because CP was positively correlated with ADF. There is a nutritional tradeoff. As deer intake higher amounts of CP to meet demands they also intake higher amounts of ADF. Also, rumen-reticulum capacity and fill must adjust to influences of pregnancy and physiological condition.