This study, conducted at the São Paulo State University feedlot, Dracena Campus, Brazil, was designed to evaluate the length of adaptation period to high concentrate diets on overall feedlot performance and carcass traits of Nellore (NE) and 1/2 Angus × Nellore (AN) cattle. The experiment was designed as a completely randomized block with 2 × 2 factorial arrangement, replicated 6 times (3 animals/pen), in which seventy-two 22-mo-old yearling bulls [36 NE, and 36 AN] were fed in 24 pens for 89 d according to the treatments: NE adapted for 9-d; NE adapted for 14-d, AN adapted for 9-d, and AN adapted for 14-d. Average initial BW was 319.2 ± 18.5 kg, and 307.9 ± 29.5 kg for NE and AN, respectively. The adaptation program consisted of ad libitum feeding of 3 diets over adaptation periods with concentrate level increasing from 62% to 86% of diet DM. Each of the adaptation diets containing 62%, 70%, and 78% concentrate was fed for 3-d to cattle adapted for 9-d. For cattle adapted for 14-d, the adaptation diets containing 62%, 70%, and 78% concentrate were fed for 5-d, 4-d and 5-d, respectively. The finishing diet contained: 66.5% cracked corn grain, 14.0% sugarcane bagasse, 16.0% cottonseed meal, 1.5% supplement, 1.2% urea, and 0.8% limestone (DM basis). Cattle were fed ad libitum twice daily throughout the study, and feed offerings and refusals were weighed daily. No significant (P > 0.10) adaptation length main effects were observed for any of the feedlot performance and carcass traits variables evaluated. However, significant (P < 0.01) biotype main effects were observed, in which AN yearling bulls had greater final BW (466.6 kg vs. 425.8 kg), ADG (1.71 kg vs. 1.27 kg), DMI expressed in kg (11.8 kg vs. 9.5 kg), and DMI expressed as % of BW (3.07% vs. 2.53%), improved G:F ratio (0.146 vs. 0.134), and heavier HCW (243.6 kg vs. 229.0 kg). No significant (P = 0.74) biotype main effect was observed for dressing percentage (AN = 53.5%; NE = 53.2%). Thus, AN yearling bulls performed better than NE yearling bulls regardless of length of the adaptation period adopted. Cattle should be adapted for 14-d, because longer adaptation periods are safer.

Grant provided São Paulo State Foundation (FAPESP), São Paulo, Brazil.