干旱区生态环境知识资源中心

Diet botanical composition, fecal nitrogen percent, and fecal phosphorus percent were determined seasonally during 1991 and 1992 for 3 cattle breeds (Barzona, Brangus, Beefmaster) grazing late-seral Chihuahuan Desert rangeland in southcentral New Mexico. These 3 cattle breeds are considered to be well adapted to harsh environments. Cattle breed main effect was non-significant (P > 0.05) for diet botanical composition. However, season main effects (P < 0.05) did occur for some diet botanical composition components. Total grasses in cattle diets were highest in January and lowest in June. Dropseeds (Sporobolus sp.), black grama (Bouteloua eriopoda Torr.), and threeawns (Aristida sp.) were the primary grasses consumed by cattle. Forb consumption was highest in June lowest in January. Honey mesquite (Prosopis glandulosa Torr.) consumption by cattle was highest in August and lowest in January. It was the primary shrub in cattle diets. Breed X season interactions (P < 0.05) occurred for a few diet botanical composition components, but the small magnitude of the values and lack of consistency prevented drawing definite management implications. Fecal nitrogen values showed differences (P < 0.05) among breeds in some seasons. However due to lack of consistency no definite conclusions could be drawn regarding superiority of 1 breed compared to another in diet nutritional quality. Both fecal nitrogen and phosphorus concentrations showed cattle diets to be lowest in quality in winter and highest in summer. From a practical standpoint, this study showed no definite advantage of any breed studied in diet botanical composition or in diet quality.