Forage quality, intake, and digestibility of year-long pastures for steers

Abstract

Thirty-six weanling steer calves (avg wt = 174 +/- 14 kg) were grazed on either wheat, irrigated improved, or native rangeland pastures from December 1989 to December 1990. Irrigated improved pastures consisted of 2 cool-season [tall wheatgrass [Agropyron elongatum (Host.) Beauv.], tall fescue (Festuca arundinacea Schreb.) 2 warm-season [bermudagrass (Cynodon dactylon (L.) Pers.], bluestem (Bothriochloa ischaemum Keng.), and annual wheat. Wheat pastures were grazed from 13 December to 11 April. Warm-season pastures were grazed from 30 May (bermudagrass) or 27 June (bluestem) until 3 October. Cool-season pastures were grazed at other days during spring and fall seasons. Rumen evacuation procedures were used to evaluate forage quality and estimate forage intake during each grazing season. Winter rangeland pastures were lower in nutritional quality (based on protein and fiber contents) and in vitro organic matter digestibility (53 vs 85%, P < 0.05) compared to wheat pasture. During spring, rangeland pastures were still lower in protein and higher in fiber but in vitro organic matter digestibility (72, 73, 72%; respectively, for wheatgrass, fescue and rangeland) was similar (P = 0.70) for all forages. Rangeland and warm-season pastures were similar in quality during summer but rangeland pastures were higher (P< 0.10) in in vitro organic matter digestibility (65, 69, and 73%; respectively, for bermudagrass, bluestem, and rangeland). Rangeland pastures were again lower in quality and digestibility than cool-season grasses during the fall. There were no difference (P>0.10) in organic matter intake (% of body weight) during winter, summer, and fall season but during spring organic matter intake was greater (P < 0.10) for steers on rangeland pasture than for those on cool-season grasses.