Utilization of Forage and Milk Energy by Angus Calves Grazing Fescue or Fescue-Legume Pastures

Utilization of forage and milk digestible energy (DE) by 153 Angus calves during the preweaning period was measured over a 4-yr period. Estimates of forage intake [internal (Cr2O3), external (H2SO4 lignin) marker techniques] and milk intake (weigh-suckle-weigh technique) were made beginning at 109, 142 and 192 d of age for each calf (5-d preliminary and 5-d collection periods). Calves were allowed either fescue-legume or fescue pastures from the time they were born (January through March) until weaned in October. Calves allowed fescue-legume grew more (P<.01) rapidly, consumed more (P<.01) milk and forage and consumed forage of higher (P<.01) energy density than calves grazing fescue pastures. Calves grazing fescue, however, were more (P<.01) efficient in conversion of milk and forage DE to weight gain than calves allowed fescue-legume pastures. Calves allowed fescue depended largely upon milk for growth whereas calves given access to fescue-legume depended more upon forage. As the calves grew, milk intake decreased and forage intake increased. The growth response per increase in milk DE ingested decreased with age whereas the growth response per increase in forage DE ingested increased. When intake was expressed as percentage of body weight, calves consuming forage of low energy density and relatively small amounts of milk did not compensate by increasing forage intake. Calves consuming forage of high energy density, however, compensated for low milk intake with increased forage intake.