Feasibility of using “days to a specific weight” traits in Nellore cattle breeding programs

SUMMARY The objective of this work was to study "days for a specific weight" traits in Nelore breeding programs comparing them with traditional traits such as average daily weight gain. Thus, this study aimed to estimate genetic parameters for days to reach 180kg (D180), days to reach 300kg (D300), pre-weaning weight gain (gpmdND), weight gain in the weaning period until yearling weight (gpmdDS) traits for a population of Nellore cattle. The used database consists in 60005 animals, and pedigree file information of 37234 growth phenotypes. The data were organized and prepared with the R program, and the estimation of (co) variance components, bi-character analyzes were performed with software Wombat. The progeny of the animals were analyzed for variability of progeny differences (Deps) by an additive genetic variation coefficient. The heritabilities for gpmdND and D180 were the highest, 0.4 and 0.45, respectively. The analysis demonstrated high genetic correlations between the traits gpmdND and D180 (0.99) and gpmdDS and D300 (0.95). D180 and gpmdDS showed the lowest coefficients of variation. Selection by the pre-weaning traits will produce animals that will take, on average, the same time to reach the weaning weight. However, for the D300 weight, the average gain was 82.44 days in relation to gpmdDS. Thus, a selection index that includes the traits D180 and D300 should produce the best results regarding the uniformity of the selected ones and the speed of gain.

摘要：本研究的核心目标为对内洛尔牛（Nelore）育种计划中的“特定体重达标天数”性状展开研究，并将其与平均日增重等传统性状进行对比；同时旨在估算内洛尔肉牛群体中，达到180kg的天数（D180）、达到300kg的天数（D300）、断奶前日增重（gpmdND）以及断奶期至周岁体重阶段增重（gpmdDS）这几个性状的遗传参数。本研究所用数据集涵盖60005头肉牛的相关资料，以及包含37234条生长表型记录的系谱文件信息。数据通过R程序完成整理与预处理，随后借助Wombat软件完成（协）方差组分估算与双性状分析。本研究通过加性遗传变异系数，对受试个体的后代开展后代差异（Deps）的变异性分析。结果显示，gpmdND与D180的遗传力最高，分别为0.4与0.45；gpmdND与D180间的遗传相关系数达0.99，gpmdDS与D300间的遗传相关系数为0.95，均表现出极强的遗传相关性。D180与gpmdDS的变异系数最低。基于断奶前性状开展选择，可培育出平均达到断奶体重所需时长一致的肉牛群体，但针对D300体重性状，相较于gpmdDS，平均达标时长多出82.44天。综上，纳入D180与D300性状的选择指数，在入选群体均匀度与增重速率两方面均可取得最优效果。