GENETIC PARAMETER AND TREND FOR PRODUCTIVE TRAITS OF NELLORE CATTLE

Abstract The Midwest region has excelled as a beef producer and producing efficiently has been the goal of livestock farmers. This study aimed to estimate the genetic parameters and trends for weights at 240(W240) and 420(W420) days of age in Nellore cattle, reared in Goias state, Brazil. A total of 48,580 data for W240 and 28,685 for W420 were used. Genetic parameters were obtained by univariate analysis. The model included the fixed effects of contemporary group (birth season-dry and wet-, year of birth, sex and farm) and covariate age of cow. Direct and maternal effects were used as random effect for W240 and the direct effect for W420. The genetic trends were obtained by regression analysis of the genetic value of the animal on the year of birth. The results of direct heritability were 0.15 ± 0.02 for W240 and 0.24 ± 0.00 for W420. The annual genetic gain was 0.311 kg for W240 and 0.511 kg for 420 days of age (W420). The results indicate the possibility of obtaining higher genetic gains through selection; however, the selection is being more efficient at W420.

摘要 中西部地区作为优质肉牛主产区表现亮眼，高效生产始终是畜牧养殖户的核心目标。本研究以巴西戈亚斯州饲养的内洛尔牛（Nellore cattle）为研究对象，旨在估算其240日龄体重（W240）与420日龄体重（W420）的遗传参数及遗传趋势。本研究共纳入W240相关数据48580条、W420相关数据28685条。遗传参数通过单变量分析计算得到，模型所纳入的固定效应包括同期组（出生季节——旱季与湿季——、出生年份、性别及养殖场均）以及母牛年龄协变量。其中，W240的随机效应包含直接遗传效应与母体遗传效应，W420仅以直接遗传效应作为随机效应。遗传趋势通过动物育种值对出生年份进行回归分析获得。W240的直接遗传力为0.15±0.02，W420的直接遗传力为0.24±0.00。W240的年度遗传增益为0.311 kg，420日龄体重（W420）的年度遗传增益为0.511 kg。研究结果显示，通过选择育种可获得更可观的遗传增益，但针对W420的选择育种效率更高。