Genetic correlation: a heritable parameter

Abstract

Breeding programs rely on selection of individuals through their breeding values to simultaneously improve multiple traits of commercial value. In order to adequately select candidates to breed for a next generation, the genetic relationships between traits are considered in the selection index that summarizes all the traits for each selection candidate. The methods deployed in genetic evaluations rely strongly in gaussian distributions describing the data, and consider the genetic relationships between traits in the form of genetic correlations determining the joint distribution of breeding values from different traits. In this manner, genetic correlations are treated as parameters, estimated on a base population for reference. However, genetic correlations depend on the involved traits’ architecture, thus depending on the genotype presented by each individual, and therefore, different individuals may present different potential for genetic correlations. Moreover, different potential for genetic correlations may partially represent a latent physiological trait responsible to balance the phenotypic expression of the measurable production traits. In practice, individual-specific genetic correlations (iSGC) can be obtained for individuals with many phenotyped descendants, as the expressed genetic correlation between the estimated breeding values among their offspring. Since the expressed iSGC depends on the involved traits’ genetic architecture, part of an individual’s iSGC can be transmitted to the offspring. In order to study the heritability of iSGC, two-trait genetic evaluations were performed on every pairwise combination of five traits from a French Holstein dairy cattle population: milk and protein yield (MY and PY), milking speed (MSPD), somatic cell score (SCS), and conception rate (CR). The iSGC between every pair of the five traits were obtained for ~1200 bulls with more than 500 phenotyped daughters in this population, and these iSGC were each evaluated as a phenotype with a single-trait model. This study confirmed the hypothesis that genetic correlations, when expressed as iSGC, are heritable parameters, with significant heritabilities ranging from 0.11 (iSGC between SCS and CR) to 0.51 (iSGC between PY and SCS).