Genetic bases of individual performance variation in pigs
Part of the variability of performances in animal production is due to the genetic variation in the level of a trait between animals; that is the keystone of all genetic improvement programs and has to be maintained to guarantee the long-term sustainability of the selection progress. Another part of the performance variability comes from the individual variation of responses to various environmental conditions, called environmental sensitivity, which can have a highly negative impact on the final profitability of the production. Joint estimations of breeding values (EBV) and genetic parameters of the individual environmental sensitivity of a trait can be obtained along with those of the level of the trait. Moreover, use of these two kinds of EBV in genetic programs partly depends on their correlations as well as their genetic relationships with other traits. In pigs, homogeneity of litter size is desired and in many cases its mean level should not decrease. Similar relationships between objectives exist for the birth weight components (mean and variability); homogeneity is desired to ensure good perinatal viability and subsequent growth, but the mean birth weight should also not decrease. The genetic parameters and relationships between components (mean and variability) of birth weight and litter size in pigs will be presented along with similar parameters estimated in a mice experiment. Furthermore, similar estimations were obtained for production traits, such as residual feed intake and growth, which will be discussed in the perspective of producing more efficient and robust animals.