The objective of this study was to evaluate the effects of adapting Nellore and ½ Angus/Nellore (AN) feedlot cattle over periods of 9 and 14 days to high-concentrate diets on performance, feeding behaviour, carcass traits and rumen morphometrics. Seventy-two yearling bulls (313.5 kg ± 24.5), 36 Nellore and 36 AN, were randomly allocated in 24 pens (3 animals/pen; 24 m² and 2.0 m of bunk space/animal) according to a randomized complete block design with a 2 × 2 factorial arrangement of treatments as follows: Nellore adapted for 9 days, Nellore adapted for 14 days, AN adapted for 9 days, and AN adapted for 14 days. Each treatment was composed by 6 pens (considered the experimental unit in this study). The adaptation lasted either 9 or 14 days and consisted of 3 step-up diets. Therefore, yearling bulls received the finishing diet containing 86% concentrate either on day 10 or 15 of the study, which lasted 89 days taking into account adaptation and finishing periods. Cattle were slaughtered in a commercial abattoir, and two 1-cm²-rumen fragments, one from cranial and another from ventral sac, were collected. The AN cattle outperformed Nellore in terms of average daily gain (1.71 kg/day vs. 1.27 kg/day, p < 0.01), gain:feed ratio (0.137 kg/kg vs. 0.127 kg/kg, p = 0.02) and hot carcass weight (243.64 kg vs. 228.98 kg, p < 0.01). No main effect of the adaptation period was observed for any of the feedlot performance and carcass traits variables evaluated. Compared to feedlot cattle adapted for 9 days, feedlot cattle adapted for 14 days sorted against long (0.68 vs. 0.91, p < 0.01) and for fine particles (1.04 vs. 1.00, p = 0.01). An interaction (p < 0.01) of genotype and adaptation period was observed for rumenitis, where Nellore bulls adapted for 14 days presented the highest scores. In conclusion, there was no evidence that either Nellore or AN cattle benefit from an adaptation period shorter than 14 days.

中文翻译：

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Nellore 和 ½ Angus/Nellore 饲养场牛在 9 天和 14 天内适应高浓度日粮的生长性能和瘤胃形态测量

本研究的目的是评估 Nellore 和 ½ Angus/Nellore (AN) 饲养场牛在 9 天和 14 天期间适应高浓度日粮对生产性能、摄食行为、胴体性状和瘤胃形态测量的影响。72 头一岁公牛 (313.5 kg ± 24.5)，36 Nellore 和 36 AN，被随机分配在 24 个围栏中（3 头动物/围栏；24 m ²和 2.0 m 的铺位空间/动物）根据随机完整区组设计，采用 2 × 2 因子处理安排如下：Nellore 适应 9 天，Nellore 适应 14 天，AN 适应 9 天，AN 适应14 天。每个处理由 6 支笔组成（在本研究中被视为实验单元）。适应持续了 9 天或 14 天，包括 3 次逐步增加的饮食。因此，一岁公牛在研究的第 10 天或第 15 天接受了含有 86% 浓缩物的育成日粮，考虑到适应期和育成期，该育成期持续了 89 天。牛在商业屠宰场被屠宰，两个 1-cm ²收集瘤胃碎片，一个来自颅骨，另一个来自腹囊。AN 牛在平均日增重（1.71 公斤/天对 1.27 公斤/天，p  < 0.01）、增重比（0.137 公斤/公斤对 0.127 公斤/公斤，p  = 0.02）和热度方面优于 Nellore胴体重量（243.64 公斤对 228.98 公斤，p  < 0.01）。对于评估的任何饲养场性能和胴体性状变量，都没有观察到适应期的主要影响。与适应 9 天的饲养场牛相比，适应 14 天的饲养场牛对长（0.68 对 0.91，p  < 0.01）和细颗粒（1.04 对 1.00，p  = 0.01）进行分类。交互（p < 0.01) 的基因型和适应期观察瘤胃炎，其中适应 14 天的 Nellore 公牛得分最高。总之，没有证据表明 Nellore 或 AN 牛从短于 14 天的适应期中受益。