COMPONENTS OF (CO)VARIANCE FOR AGE AT FIRST AND SECOND CALVING OF NELLORE FEMALES RAISED IN SOUTHERN BRAZIL

Abstract The objective of this study was to estimate the heritability, genetic correlation and estimated breeding values for age at first (AFC) and second calving (ASC) for Nellore females raised in Southern Brazil. The (co)variance and estimated breeding values were obtained using Bayesian inference in a bivariate analysis, adopting an animal model. The average ages were 49.30 and 69.85 months, and the heritabilities were 0.25 and 0.26, respectively for AFC and ASC. The genetic correlation between AFC and ASC was 0.88. The correlation between the classifications of sires according to their estimated breeding values was 0.93. The heritability estimates for AFC and ASC suggest the possibility of obtaining genetic gain by selection. The correlation between these traits close to one indicates that they are virtually controlled by the same genes, and the selection for one of them will promote correlated advanced gain for the other.摘要 本研究旨在评估巴西南部饲养的内罗尔母牛首次产犊年龄（Age at First Calving, AFC）与第二次产犊年龄（Age at Second Calving, ASC）的遗传力、遗传相关系数与估计育种值。本研究采用动物模型开展双变量分析，借助贝叶斯推断获取（协）方差组分与估计育种值。两类性状的平均年龄分别为49.30个月与69.85个月，AFC与ASC的遗传力分别为0.25与0.26。AFC与ASC的遗传相关系数为0.88；基于估计育种值对种公牛进行分级的相关系数为0.93。AFC与ASC的遗传力估算结果表明，通过选择可获得遗传进展。上述两性状间的相关系数接近1，提示二者实质上受相同基因调控，对其中一项性状开展选择，将对另一性状带来正向相关遗传进展。