Genetic parameters and accuracy of traditional and genomic breeding values for eye pigmentation, hair coat and breed standard in Hereford and Braford cattle

The objectives of this research were to estimate genetic parameters using a threshold animal model by traditional (pedigree and phenotype) and single-step genomic BLUP methodologies, and assess breeding value accuracy gains with the inclusion of genomic information for eye pigmentation (EP), hair coat at weaning (HW) and yearling (HY) and breed standard (BS) in Hereford and Braford cattle. The relationship of these traits with tick resistance was also evaluated. The data used in this study were obtained from Conexão Delta G breeding program and belong to animals born between 1991 and 2014, totaling 169,839 individuals in the pedigree data, 73,615 phenotypes for EP, 81,043 for HW, 41,390 for HY, 28,186 for BS and 16,621 for tick count (TC). The genotypic data, after quality control, retained 41,011 SNP markers and 3,954 samples, including 2841 Braford and 909 Hereford animals with phenotypic records for at least one of the considered traits. Estimated heritabilities through traditional and genomic methods ranged from high to medium magnitude, being, respectively 0.46 ± 0.02 and 0.46 ± 0.02 for EP, 0.44 ± 0.03 and 0.44 ± 0.03 for HW, 0.42 ± 0.02 and 0.41 ± 0.02 for HY and 0.33 ± 0.02 and 0.32 ± 0.02 for BS. Genetic correlations among all traits were of low magnitude (-0.23 < rg < 0.29), except between HW and HY (0.62). The use of genomic information provided higher accuracy levels with gains of 0.28 and 0.14 for EP, 0.13 and 0.07 for HW, 0.16 and 0.30 for HY and 0.10 and 0.04 for BS traits, respectively considering k-means and random grouping cross-validation strategies. Thus, it is possible to obtain genetic gains in adaptation through selection for the studied traits. High genetic correlation between the hair coat evaluated at weaning and yearling indicates that selection for these traits can be performed in advance at weaning. Although low, the favorable correlations between adaptation traits favors the selection of animals that are more adapted to the tropical environmental conditions, using correlated responses to increased eye pigmentation and reduced hair coat and tick count simultaneously. The prediction of breeding values using genomic information by the single-step method should result in more accurate predictions compared to traditional pedigree evaluations.