ABSTRACT
Summary Forage allocation to mixtures of large herbivores is accomplished by minimizing the difference between the available herbage and the required forage for animals on rangeland. Availability is determined in part by the plant's physiological tolerance to grazing or its allowable-use factor and the animal preference for that plant, measured in part by the proper-use factor. The mix of large herbivores on the rangeland must also be considered. The grazing requirements for animals are dependent on animal preference for plant species and on the total forage intake rates. This paper presents an analysis of these concepts and published information. The concept of proper-use factor is widespread, but published methodologies for its formulation are lacking. Allowable-use factors, determined primarily in clipping studies, are generally higher than proper-use factors, but the exact relationship between them is unclear at best. Preference for plants by herbivores, as defined in the literature, varies in meaning from percentage eaten by forage class (grasses, forbs, and shrubs) to rankings by percent of plant species in herbivore diets to actual calculation of a preference index. The method used to calculate a preference index can yield varying results and interpreta
365tions. Forage intake-rate studies that use animals under grazing rather than under pen conditions appear to be confined to domestic sheep and cattle. Some 52 intake-rate values for cattle averaged 2.2% of body weight/day; 53 intake-rate values for sheep averaged the same. We also report forage intake rates for pronghorn antelope, bison, bighorn sheep, mule deer, horses, and elk. Through understanding of these variables, effective management strategies may be derived whereby the rangeland resource can be used prudently without degradation.
