Methods of Estimating Dry-Weight Composition in Diets of Steers

The species of plants in the diets of grazing animals must be accurately determined in order to efficiently manage the grazing animal and, hence, the range ecosystem. Since animals select forage from a variety of species of plants and parts of plants, procuring estimates of the quantity and quality of plants in the diets of herbivores has been a difficult sampling problem. However, this information is essential for devising optimal grazing and supplementation plans (Cook and Harris, 1950). The intent of this study was to compare the “microscope technique” and the “bitecount method” for estimating dry-weight composition of plant species in the diets of steers grazing sandhill range in eastern Colorado. Sparks and Malechek (1968) showed that dry-weight percentages of individual species of plants could be estimated in mixtures of grasses, forbs, and grass-forb combinations by a microscopic examination of histological characteristics of plant tissue. They accurately estimated the dry-weight composition of known mixtures of plants commonly found in the diets of herbivores (r2=.98).