This study, conducted at the São Paulo State University feedlot, Botucatu Campus, Brazil, was designed to determine the effects of adaptation periods of 6, 9, 14 and 21 d on feedlot performance and carcass traits of Nellore cattle. Cattle were fed for 88-d regardless of adaptation period adopted. The experiment was designed as a completely randomized block, replicated 6 times, in which ninety-six 20-mo-old yearling Nellore bulls (391.1 ± 30.9 kg) were fed in 24 pens (4 animals/pen) according to the different adaptation periods adopted: 6, 9, 14, and 21 d. The adaptation program consisted of ad libitum feeding of 3 diets over adaptation periods with concentrate level increasing from 70% to 86% of diet DM. Each of the adaptation diets containing 70.0%, 75.0%, and 80.5% concentrate were fed for 2-d, 3-d and 7-d to cattle adapted for 6-d, 9-d and 21-d; respectively. Also, the adaptation diets containing 70.0%, 75.0%, and 80.5% concentrate were fed for 4-d, 5-d and 5-d, respectively, to cattle adapted for 14-d. The finishing diet contained: 71.5% cracked corn grain, 14.0% sugarcane bagasse, 10.5% peanut meal, 2.5% supplement, 1.0% urea, and 0.5% limestone (DM basis). Cattle were fed ad libitum twice daily throughout the study, and feed offerings and refusals were weighed daily. Orthogonal contrasts were used to evaluate linear, quadratic, and cubic relationship between adaptation periods and the dependent variable. The use of different adaptation periods did not affect (P > 0.10) DMI, either expressed in kg or as % of BW. However, as the adaptation period lasted longer, final BW (6-d = 512.0 kg; 9-d = 521.9 kg; 14-d = 527.6 kg; 21-d = 514.8 kg), ADG (6-d = 1.37 kg; 9-d = 1.48 kg; 14-d = 1.56 kg; 21-d = 1.41 kg), G:F ratio (6-d = 0.142; 9-d = 0.153; 14-d = 0.153; 21-d = 0.146), and HCW (6-d = 277.3 kg; 9-d = 283.3 kg; 14-d = 287.8 kg; 21-d = 283.3 kg) were affected (P < 0.05) quadratically. Moreover, dressing percentage increased linearly (P = 0.05), as the adaptation period lasted longer (6-d = 54.13%; 9-d = 54.27%; 14-d = 54.55%; 21-d = 55.04%). Thus, yearling Nellore bulls should be adapted for 14 d.

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