The objectives were to conduct a genetic evaluation of residual feed intake (RFI) and residual feed intake adjusted for fat (RFIFat) and to analyse the effect of selection for these traits on growth, carcass and reproductive traits. Data from 945 Nellore bulls in seven feed efficiency tests in a feedlot were analysed. Genetic evaluation was performed using an animal model in which the feed efficiency test and age of the animal at the beginning of the test were considered as a systematic effect. Direct additive genetic and residual effects were considered as random effects. Correlations and genetic gains were estimated by two-trait analysis between feed efficiency measures (RFI and RFIFat) and other traits. Feed conversion showed low heritability (0.06), but dry matter intake (DMI), average daily gain, RFI, RFIFat, metabolic body weight and scrotal circumference measured at 450 days of age (SC450) showed moderate to high heritability (0.49, 0.28, 0.33, 0.36, 0.38 and 0.80, respectively). Similarly, ribeye area, backfat thickness, rump cap fat thickness, marbling score and subcutaneous fat thickness also had high heritability values (0.46, 0.37, 0.57, 0.51 and 0.47, respectively). Genetic correlations between RFI and SC450 were null, and between RFIFat and SC450 were strongly positive. Genetic and phenotypic correlations of RFI and RFIFat with carcass traits were not different from zero, as correlated responses for carcass traits were also not different from zero. The Nellore selection for feed efficiency by RFI or RFIFat allows the recognition of feed efficient animals, with DMI reduction and without significant changes in growth and carcass traits. However, because of the observed results between RFIFat and SC450, selection of animals should be analysed with caution and a preselection for reproductive traits is necessary to avoid reproductive impairments in the herd.

中文翻译：

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饲料效率的选择不会改变 Nellore 牛生长和胴体性状的选择

目的是对剩余采食量 (RFI) 和脂肪调整后剩余采食量 (RFIFat) 进行遗传评估，并分析选择这些性状对生长、胴体和繁殖性状的影响。分析了来自 945 头 Nellore 公牛在饲养场的七次饲料效率测试中的数据。使用动物模型进行遗传评估，其中饲料效率测试和测试开始时动物的年龄被视为系统效应。直接加性遗传和残余效应被认为是随机效应。通过饲料效率测量（RFI 和 RFIFat）和其他性状之间的双性状分析来估计相关性和遗传增益。饲料转化率显示低遗传力 (0.06)，但干物质摄入量 (DMI)、平均日增重、RFI、RFIFat、在 450 日龄时测量的代谢体重和阴囊周长 (SC450) 显示出中等至高度的遗传性（分别为 0.49、0.28、0.33、0.36、0.38 和 0.80）。同样，肋眼面积、背膘厚度、臀盖脂肪厚度、大理石花纹评分和皮下脂肪厚度也具有较高的遗传力值（分别为 0.46、0.37、0.57、0.51 和 0.47）。RFI 和 SC450 之间的遗传相关性为零，而 RFIFat 和 SC450 之间的遗传相关性呈强正相关。RFI 和 RFIFat 与胴体性状的遗传和表型相关性不为零，因为胴体性状的相关响应也不为零。通过 RFI 或 RFIFat 对饲料效率的 Nellore 选择允许识别饲料效率高的动物，DMI 减少，生长和胴体性状没有显着变化。然而，