Technical Note: Physical factors that influence fecal analysis estimates of herbivore diets

Abstract

Microhistological analysis of epidermal fragments in feces is often used to estimate the diet of herbivores but is not generally accepted as a consistently reliable method. Gross errors arise, especially when diets are composed of herbage components with widely different morphological and structural characteristics. The present study investigated the possibility of using such physical characteristics to improve the reliability of the method. Over a 7 day period, 4 rumen-fistulated beef cows were given a fixed diet composed of a shrub, a grass, and a forb component. On the last 2 days, samples of rumen content and feces were taken for analysis of epidermal fragment. Forbs were under-estimated, grasses over-estimated, and shrubs correctly estimated. Correction factors to estimate true diet composition were defined as the biomass represented by the specific epidermal fragments (epidermal weight index) and the degree of degradation to which the epidermis is subjected in the digestion process (epidermal erodibility factor). These factors account for characteristic physical features of the different dietary components and were measured directly or were derived from the calibration experiment. The utility of such factors depends on accurate determination of the component variables and may be overshadowed by sampling error and observer bias in the microhistological identification of epidermal fragments.