Cattle Grazing Blue Grama Rangeland. II. Seasonal Forage Intake and Digesta Kinetics

Abstract

Four field trials were conducted from early August to late October, 1982, on blue grama (Bouteloua gracilis) rangeland in south-central New Mexico, to examine relationships among grazing season, forage intake and digestive function in beef steers (Bos taurus). Organic matter intake declined from 24.0 g/kg body weight (BW) in early August to 17.4 g/kg BW in late September and then increased to 20.9 g/kg BW in the early dormant season (late October). From early growing season to early dormancy, diet digestibility and passage rates decreased while retention time of digesta in the rumen increased. Rate and extent of in vitro organic matter disappearance were 66.5, 6.7; 63.1, 6.7; 51.6, 4.8; and 47.9%, 5.6%/hour in early August, late August, late September and late October, respectively. Fluid and particulate passage rates (%/hour) were 24.9, 4.6; 12.7, 3.9; 11.1, 3.7; and 10.5, 3.5, respectively, for the same periods. Retention of particulate digesta varied from 26.1 hours in the early growing season to 34.3 hours in early dormancy. Gastrointestinal fill gradually increased as season progressed. Results suggest that maintenance of a diverse plant community, containing not only desirable grasses but also palatable forbs, may allow cattle to maintain a higher level of nutrient intake during periods of grass dormancy.