Herbage Intake Rates of Beef Cattle Grazing Alfalfa1

Alfalfa (Medicago sativaL.), a forage crop unique in that it has high potential in terms of both yield and quality, has considerable capacity for animal production when grazed under management that is based on its growth and development. Two grazing experiments, using balanced change‐over designs, were set up to measure the ingestive behavior of beef heifers (Bos taurus) during the first, second, and third hours of grazing sessions on alfalfa pastures established on Maury silt loam (fine, mixed, mesic Typic Paleudalfs). In Exp. I where the herbage mass, in terms of dry matter (DM), was 3.06 Mg ha−1and the herbage DM allowance was 6.1 kg h−1per heifer, animals ingested DM at 2.96, 1.88, and 1.56 kg h−1during their first, second, and third hours of grazing, respectively. The mean rates of biting were 26, 21, and 19 bites min−1for the same periods. Herbage DM intake per bite declined linearly from 1.96 to 1.54 to 1.36 g for each hour increment in grazing time. Forage utilization was 51, 32, and 27% for the same increments. In Exp. II where the herbage mass (DM) was 1.74 Mg ha−1and the allowance was 3.4 kg h−1, heifers ingested 2.35, 1.47, and 1.20 kg h−1during their first, second, and third hours of grazing, respectively. The mean rates of biting were 34, 22, and 18 bites min−1during the same periods within the grazing session. Herbage DM intake per bite averaged 1.17 g and did not vary within the grazing session. Forage utilization was 75, 47, and 37% during the three consecutive hours within the grazing session. Maximum rates of herbage intake were characterized by larger bites and relatively slow rates of biting. Rates of herbage intake were considerably higher during the first hour of grazing than during the second and third hours. In a 3‐h grazing session, animals consumed 47, 29, and 24% of their intake during the first, second, and third hours, respectively.