Genetic parameters for reproduction and growth traits in Boer goats in Brazil

Abstract

Data collected over a period of 15 years in a herd of Boer goats in Brazil were used to estimate genetic parameters for reproductive and growth traits. The analyses included weights of about 1300 kids and nearly 750 reproductive records by 345 goats. The mixed model analyses of reproductive traits (kidding interval, litter size, litter weight at birth and weaning, doe weight at parturition) included the fixed effects of contemporary group and parity, and the random effects of additive genetic and permanent environmental effects. For growth traits (birth weight, weaning weight, average daily gain and relative growth rate) the fixed effects considered were contemporary group, sex, number born and parity, while the random effects were the direct and maternal genetic effects (allowing for their covariance), permanent environmental effect of the dam and litter common environmental effect. The mean performance in the Boer goats included in our study was 56.4±11.5kg for live weight at parturition, 456±198days for kidding interval, 1.70±0.66 kids for litter size, 5.8±2.2 and 23.4±9.7kg for litter weight at birth and weaning, respectively, while the kids had means for birth and weaning (112 days) weight of 3.4±0.8 and 15.2±4.7kg, with average daily gain and relative growth rate of 105.2±40.0g and 1.3±0.3%, respectively. The heritability (h2) estimate for reproductive traits was near zero for litter size and litter weight at birth, about 0.1 for kidding interval and litter weaning weight, and close to 0.4 for doe weight at parturition. The estimated repeatability was about 0.5 for doe weight at parturition and near 0.1 for all the other reproductive traits. The h2 of direct effects for growth traits was consistently higher than h2 of maternal effects. For birth weight, h2 estimates of direct and maternal effects were smaller than for the other traits, in the range of 0.05 to 0.08. For growth and weight traits measured after birth, h2 of direct effects ranged from 0.23 to 0.31, and h2 of maternal effects was about 0.13 for the various traits. There was a strong antagonism between direct and maternal effects, with a genetic correlation of −0.67 for birth weight, and about −0.8 to −0.9 for the other traits. Relative to the phenotypic variance, the influence of the permanent environmental effect of the dam represented about 0.11–0.15 and the common environmental effect of the litter corresponded to 0.32 for birth weight and ranged from 0.13 to 0.18 for the other traits. These results indicate that selection for some reproductive traits such as litter size may be difficult, given the low levels of genetic variability, but could be more successful for other traits like litter weaning weight and kidding interval. Selection for weight at and growth rate up to weaning should take into account the importance of direct and maternal genetic effects as well as the genetic antagonism between these two components. Factors which are seldom considered in mixed model analyses, such as the common litter effect, were found to be of major importance, and must be considered in the linear models used to estimate genetic parameters and predict breeding values in meat goats.