USE OF RANDOM REGRESSION MODELS FOR ESTIMATION OF GENETIC PARAMETERS IN TABAPUÃ CATTLE

Abstract In this study 28,643 weight records taken from birth to 660 days of age from 6,471 animals of the Tabapuã zebu breed were used to estimate (co)variance components and genetic parameters using a random regression model. The data were analyzed with the DFREML program applying the Restricted Maximum Likelihood method and using an AIREML algorithm. In the models, direct additive genetic, maternal, and permanent environmental (animal and maternal) effects were assumed to be random, contemporary groups were included as fixed effects, and the ages of animal at weighing and of dam at calving were used as covariables. Estimates of direct additive genetic variance increased with age. Heritability estimates for direct additive effect decreased from birth to weaning, whereas estimates of maternal heritability increased over this period and decreased at older ages. Direct genetic correlations ranged from moderate to high, so their magnitudes decreased with greater age gaps between animals. The random regression model used in this study was appropriate to describe changes in variance estimates for weights in Tabapuã cattle raised in the Brazilian state of Bahia.

摘要 本研究使用了来自6471头塔巴普阿瘤牛（Tabapuã Zebu）从出生至660日龄的28643条体重记录，采用随机回归模型（Random Regression Model）估算（协）方差组分与遗传参数。数据分析采用DFREML软件，应用受限最大似然法（Restricted Maximum Likelihood）并结合AIREML算法完成。模型中设定直接加性遗传效应、母体遗传效应以及永久环境（动物与母体）效应为随机效应，将同期组作为固定效应，并以家畜称重时的日龄及母牛产犊时的日龄作为协变量。研究结果显示，直接加性遗传方差的估计值随日龄增长而升高。直接加性效应的遗传力估计值从出生到断奶阶段呈下降趋势，而母体遗传力估计值在此阶段逐步升高，在更高日龄时则出现下降。直接遗传相关系数处于中等至较高水平，其数值随个体间日龄间隔的增大而降低。本研究所采用的随机回归模型，可有效描述巴西巴伊亚州饲养的塔巴普阿瘤牛体重方差估计值随日龄的变化规律。