Rumen-reticulum capacity and fill in female white-tailed deer: Meeting demands in a stochastic environment

Background/Question/Methods

Understanding capacity and fill dynamics of the gastrointestinal tract under differing environmental conditions gives insight into how large mammalian herbivores physiologically adjust to meet life history demands.  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.  We collected 84 adult female white-tailed deer (Odocoileus virginianus) in March, September, and November, 2009-2011, from Kerr Wildlife Management Area, Kerr County, Texas, USA.  From each animal we measured rumen-reticulum capacity and fill (wet and dry), body weight, body condition, dietary nutrition, and determined reproductive state.  We built models and used Akaike Information Criteria to select models to explain rumen-reticulum capacity and fill dynamics. 

Results/Conclusions

Rumen-reticulum capacity and dry rumen-reticulum fill fluctuated with reproductive state and dietary nutrition.  Wet rumen-reticulum fill fluctuated with the animal’s body condition, dietary nutrition, and reproductive state.  Pregnant deer had significantly smaller rumen-reticulum capacities and fill indicating a restriction in food intake late in the third trimester of pregnancy.  Lactating deer only had a slight increase in rumen-reticulum capacity and fill.  Deer with a lower body condition score had larger amounts of rumen-reticulum fluid (wet rumen-reticulum fill minus dry rumen-reticulum fill).  Rumen-reticulum capacity decreased with higher amounts of CP but increased with higher amounts of ADF.  However, wet and dry rumen-reticulum fill increased with higher amounts of CP because CP was positively correlated with ADF.  There is a nutritional tradeoff in free-ranging deer.  As deer intake higher amounts of CP to meet demands, they also intake higher amounts of ADF.  Rumen-reticulum capacity must adjust to the influences of reproductive state and dietary nutrition while accommodating fluctuations in wet-rumen-reticulum fill due to the body condition, reproductive state, and dietary nutrition in order for female white-tailed deer to meet life history demands.