An evaluation of three methods for determining diet quality of free-ranging small herbivorous mammals

Abstract

Pocket gophers (Thomomys bottae) were fed one of seven diets spanning a wide range of nutrient content and dry matter digestibility to evaluate three methods of assessing diet quality in small herbivorous mammals: the ash tracer method, prediction equations based on stomach composition, and prediction equations based on fecal composition. The ash tracer method was a poor predictor of dry matter digestibility because (i) total ash content of the stomach contents was only weakly correlated with the total ash content of the diet and (ii) total ash digestibility varied considerably between diets and was in part dependent on the dry matter digestibility of the diet. In contrast, neutral detergent soluble content of the stomach contents and of the feces was a good predictor of dietary neutral detergent soluble content and dry matter digestibility. Fecal nitrogen was a good predictor of dietary nitrogen although it was less reliable in predicting dry matter digestibility. Stomach content crude fat, ash, and nitrogen concentrations were poor predictors of both dietary nutrient content and dry matter digestibility, as were colon content and fecal crude fat and ash concentrations. None of the indices tested were reliable predictors of dry matter intake.