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.

研究概况：本研究旨在对内洛尔肉牛（Nelore）育种计划中的达目标体重日龄性状展开研究，并与平均日增重（average daily weight gain）等传统育种性状开展对比分析。据此，本研究旨在估算内洛尔肉牛群体中达180千克日龄（days to reach 180kg，D180）、达300千克日龄（days to reach 300kg，D300）、断奶前日增重（pre-weaning weight gain，gpmdND）以及断奶至周岁增重（weight gain in the weaning period until yearling weight，gpmdDS）这4个性状的遗传参数。本研究所用数据库包含60005头受试动物的相关数据，以及涵盖37234条生长表型信息的系谱文件。数据的整理与预处理工作借助R语言程序完成，而（协）方差组分估计与双性状分析均通过Wombat软件开展。本研究通过加性遗传变异系数，分析了受试动物后代的后代差异（progeny differences，Deps）变异程度。gpmdND与D180的遗传力最高，分别为0.4与0.45。分析结果显示，gpmdND与D180间存在极高的遗传相关（0.99），gpmdDS与D300间的遗传相关系数为0.95。D180与gpmdDS的变异系数最低。基于断奶前性状开展选择，可获得平均达到断奶体重所需时长一致的个体。但针对D300体重性状，相较于gpmdDS，平均所需时长多出82.44天。因此，纳入D180与D300性状的选择指数，在提升选留个体均匀度与增重速度方面可取得最优效果。