Abstract
The knowledge of genetic trends and trade-offs between growth and reproductive traits might be useful to understand the evolution of these traits in livestock and natural populations of animals. We estimated the genetic trends and trade-offs between pre-weaning growth and calving intervals of Nellore animals from a commercial farm. Two-trait animal models were used to estimate covariance components and breeding values (EBV) for direct and maternal genetic effects of pre-weaning growth and direct genetic effects of calving intervals. Regression analyses were performed to examine the relationship between direct and maternal EBV of pre-weaning growth and direct EBV of calving intervals (dependent variables) and the coefficient of generation of each animal (independent variable). We also performed regression analyses to examine the relationship between direct EBV of calving intervals (dependent variables) and direct and maternal EBV of pre-weaning growth (independent variables). The genetic trends for direct and maternal genetic effect for pre-weaning growth were significant and presented genetic evolution in the studied Nellore herd. The genetic trends for the reproductive traits were also significant but indicated genetic changes in an unfavorable way. The genetic correlations between direct effects of pre-weaning growth and calving intervals traits and the genetic correlations between maternal effects of pre-weaning growth traits and direct effects of calving interval traits were not different from zero. The presence of trade-offs between the direct effects of growth and reproductive traits were confirmed through regression from direct EBV of calving intervals over EBV of pre-weaning growth traits. In addition, regression analyses showed that selection to increase pre-weaning growth also increased calving intervals. Our results showed that pre-weaning growth and calving intervals are increasing over generations and that trade-offs occurred between those traits in the studied Nellore herd.
Highlights
Animal growth is important in livestock production and in natural populations because it is related with economic profit and adaptation [1,2,3]
The maternal effect evaluation is mainly performed by pre-weaning growth traits because this is the moment that the calves are more dependent of the cows for feeding and protection
It is related to milk production and to parental investment that cows do in order to improve offspring performance [8,9], and it has genetic and environmental components [1]
Summary
Animal growth is important in livestock production and in natural populations because it is related with economic profit and adaptation [1,2,3]. Direct and maternal genetic effects affect growth. The direct genetic effects is the sum of the additive effects of each gene affecting a certain trait [6,7]. The maternal effect evaluation is mainly performed by pre-weaning growth traits because this is the moment that the calves are more dependent of the cows for feeding and protection. It is related to milk production and to parental investment that cows do in order to improve offspring performance [8,9], and it has genetic and environmental components [1]
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