Influence of range site on diet selection and nutrient intake of cattle.

Abstract

It is common in range science to base stocking rate estimates on range sites as units of forage production. However, little is known about how diet composition, quality, and intake may differ by range site. This study examines the influence of 2 range sites on the diet selection and nutrient intake of cattle. A sandy loam (SL) and a clay loam (CL) range site were compared in 4 seasonal, trials on an Acacia dominated, mixed-brush savanna on the Texas Rio Grande Plains. Diet composition and quality, and nutrient intake of cattle were determined throughout each 16-21 day trial using esophageally fistulated cattle and daily dosing with ytterbium acetate. The range sites differed widely in proportions of grass, forb, and browse biomass. Cattle generally selected similar diets and adjusted diets to increasing grazing pressure and decreasing forage availability in a similar manner regardless of site, except in fall when cattle selected more browse on the SL site where herbaceous forage was severely limited. Fecal output of cattle differed between sites only in fall when cattle on the SL site had lower fecal output than cattle on the CL site. Cattle on the site of lower herbaceous mass (SL site) generally achieved higher diet quality and nutrient intake during the growing season, when herbaceous forage was readily available because of greater access to green forage. Therefore, the SL site yielded higher diet quality at low grazing pressure during the growing season. Conversely, the CL site, because of its greater herbaceous mass, yielded higher nutrient intake in the fall and at high levels of grazing pressure.