This research evaluated the effect of supplementation with cracked corn grain (0 or 1% of liveweight) on the performance of Hereford steers grazing a mixed pasture of legume and grass at 3 forage allowances (3, 6 or 9 kg DM/100 kg liveweight). The experiments were conducted in West Uruguay over 2 consecutive summers, with 72 Hereford steers (282 ± 15.3 kg; n = 36/year) randomly allocated to 1 of the 6 treatments in a factorial arrangement. Cattle were supplemented in individual pens and weighed every 14 days. Grain intake did not differ (P>0.05) between forage allowances. Both supplementing and increasing forage allowance reduced (P<0.01) forage utilisation. Year effect was significant (P<0.01) for liveweight gain and grain intake, but neither the 2- nor the 3-way interaction of year with forage allowance or supplementation was significant (P>0.05). Increasing forage allowance only improved (P<0.01) liveweight gain of non-supplemented cattle (0.299, 0.483, 0.667 kg/day for forage allowance of 3, 6 or 9%, respectively). Hence, response to supplementation decreased with forage allowance, increasing the grain (kg)/gain (kg) conversion ratio. These results provide a quantitative basis on which to decide upon the best feeding management option for summer.
