The energy content of finishing diets offered to feedlot cattle may vary across countries. We assumed that the lower is the energy content of the finishing diet, the shorter can be the adaptation period to high-concentrate diets without negatively impacting rumen health while still improving feedlot performance. This study was designed to determine the effects of adaptation periods of 6, 9, 14 and 21 days on feedlot performance, feeding behaviour, blood gas profile, carcass characteristics and rumen morphometrics of Nellore cattle. The experiment was designed as a completely randomised block, replicated 6 times, in which 96 20-month-old yearling Nellore bulls (391.1 ± 30.9 kg) were fed in 24 pens (4 animals/pen) according to the adaptation period adopted: 6, 9, 14 or 21 days. The adaptation diets contained 70%, 75% and 80.5% concentrate, and the finishing diet contained 86% concentrate. After adaptation, one animal per pen was slaughtered (n = 24) for rumen morphometric evaluations and the remaining 72 animals were harvested after 88 days on feed. Orthogonal contrasts were used to assess linear, quadratic and cubic relationships between days of adaptation and the dependent variable. Overall, as days of adaptation increased, final BW (P = 0.06), average daily gain (ADG) (P = 0.07), hot carcass weight (P = 0.04) and gain to feed ratio (G : F) (P = 0.07) were affected quadratically, in which yearling bulls adapted by 14 days presented greater final BW, ADG, hot carcass weight and improved G : F. No significant (P > 0.10) days of adaptation effect was observed for any of feeding behaviour variables. As days of adaptation increased, the absorptive surface area of the rumen was affected cubically, where yearling bulls adapted by 14 days presented greater absorptive surface area (P = 0.03). Thus, Nellore yearling bulls should be adapted by 14 days because it led to improved feedlot performance and greater development of rumen epithelium without increasing rumenitis scores.

为饲养场牛提供的育肥日粮的能量含量可能因国家而异。我们假设最终日粮的能量含量越低，对高浓度日粮的适应期就越短，而不会对瘤胃健康产生负面影响，同时仍能提高饲养场的性能。本研究旨在确定 6、9、14 和 21 天的适应期对 Nellore 牛饲养场性能、饲养行为、血气特征、胴体特征和瘤胃形态测量的影响。实验设计为完全随机区组，重复 6 次，其中 96 只 20 月龄内洛尔公牛 (391.1 ± 30.9 kg) 根据所采用的适应期在 24 个围栏（4 只动物/围栏）中饲养：6 、9、14 或 21 天。适应日粮含有 70%、75% 和 80.5% 的浓缩物，最终日粮含有 86% 的浓缩物。适应后，每栏屠宰一只动物（n = 24) 用于瘤胃形态评估，其余 72 只动物在饲喂 88 天后收获。正交对比用于评估适应天数与因变量之间的线性、二次和三次关系。总体而言，随着适应天数的增加，最终体重 ( P = 0.06)、平均日增重 (ADG) ( P = 0.07)、热胴体重量 ( P = 0.04) 和增重比 (G : F) ( P = 0.07 ) 受到二次影响，其中适应 14 天的一岁公牛表现出更高的最终 BW、ADG、热胴体重量和改进的 G：F。无显着性 ( P> 0.10) 天的适应效应观察到任何喂养行为变量。随着适应天数的增加，瘤胃的吸收表面积受到立方影响，其中适应14天的一岁公牛呈现出更大的吸收表面积（P = 0.03）。因此，内洛尔一岁公牛应该适应 14 天，因为它可以改善饲养场性能和瘤胃上皮的更大发育，而不会增加瘤胃炎评分。