Forage Intake and Performance of Lactating Beef Cows Grazing High or Low Quality Pastures1

Forage digestibility, intake and animal performance (cow and calf weight and fatness change, cow milk production and milk composition) were measured for 79 lactations of Angus cows during a 2-year period. Cows grazed either tall fescue-legume pastures clipped at regular intervals (high quality) or tall fescue pastures allowed to mature (low quality). Digestibility and intake were estimated by the internal (acid detergent lignin)-external (Cr2 03) indicator ratio technique continuously from April 29 to September 28 (152 days) each year. Cows grazing high quality pastures consumed 1.7 kg/day more DM (10.5 vs 8.8 kg/day, P<.01) and 1.3 kg/day more digestible DM (6.4 vs 5.1 kg/day, P<.01) than cows grazing low quality pastures. Forage consumed from high quality pastures was 2.5 percentage units higher in DM digestibility (60.8 vs 58.3%, P<.01) than was forage consumed from low quality pastures. Pasture quality differences were the result of large advantages for the high quality pastures during the summer. Cows on both pasture qualities, however, produced similar (P>.82) amounts of milk although milk from those on high quality pastures contained .42 percentage units more (P<.04) butterfat. During the experimental period cows on high quality pastures gained 18 kg more (P<.01) weight and 2.8 mm more (P<.01) subcutaneous fat than those on low quality pastures. They also weaned calves that were 18 kg heavier (P<.01) at adjusted 240-day calf age.