This work had as objective to validate the computer program of Sistema Viçosa de Formulação de Rações, as well as the 1996 beef NRC, including levels 1 (NRC system) and 2 (Cornell System) for growing beef cattle under pastures. The data of daily gain predicted by the programs as a function of body weight, genetic groups and supplements composition and intake during the dry season were compared to the observed values. The levels 1 and 2 of NRC system underpredicted dry matter intake in 12 and 13% and daily gain in 55 and 86%, respectively, of 35 supplemented steers in tropical pastures during the dry season. The Viçosa system overpredicted intake in 5% and underpredicted daily gain in 11%, with lower error. In a second validation assay with a data base of 25 experiments, 74 treatments and 1230 animals, the Viçosa system overpredicted the daily gain as a function of energy intake (TDN), in 44%. In spite of that, the program is adequate to be utilized in formulation of feed supplements for growing bovines in tropical pastures, as feed intake and so, daily gain are highly variable, due to variation in pastures availability and composition, and diversity of climate and animal genetic.
daily gain; database; intake; pasture; urea
