Objective: To develop three models in order to estimate the defecation rate ofwhite-tailed deer (Odocoileus virginianus) according to the season of the year,content of neutral detergent fiber (NDF), and acid detergent fiber (ADF) in feces.Design / methodology / approach: Nine captive adult deer were assigned tothree levels of dietary fiber. Fecal groups (defecation rate) were counted, forageconsumption was estimated, and feces were analyzed for NDF and ADF content. Arandomized block design was used, where the effect of the treatments was blockedby season, and a multiple regression analysis was used to define the predictionmodels of the defecation rates.Results: The rates were different for dietary fiber levels (p<0.0001), and for theyear season (p = 0.0007). For spring, the defecation rate model (DR) was DR = -4.84696 - [0.02159 (NDF)] + [0.58397 (ADF)]; for summer DR = -51.0272 +[0.26868 (NDF)] + [1.61121 (ADF)]; and for winter DR = 7.82939- [0.02667 (NDF)]+ [0.17309 (ADF)].Limitations / implications: Defecation rate or fecal group counting is a useful toolto estimate deer populations. Nevertheless, the definition of an adequatedefecation rate represents a hard task, since it depends on various factors such asthe environmental conditions, and the components of the diet the deer consumes.Findings / conclusions: The defecation rate varies depending on the year seasonand the fiber content in the diet.