Genetic parameters for milk production and body-conformation traits in Dairy Gir cattle

Context Gir is a tropically adapted breed of Bos taurus indicus cattle that has been intensively selected for milk production in Brazil. Selection programs also consider body-conformation traits because these have been associated with health, welfare, and cow longevity, thus affecting productivity.Aims This study focused on Gir cattle to estimate genetic and phenotypic parameters for body-conformation traits, as well as their correlations with milk production traits.Methods Body-conformation traits were classified as 'frame', 'foot and leg', or 'mammary system' traits. The dataset contained 1105 cows recorded with body-conformation traits and 38 996 records of 305-day cumulative milk yield, from 24 489 Gir cows. The pedigree file included 38 571 animals, of which 1593 were genotyped using six different single-nucleotide polymorphism panels. After genotyping imputation, and quality control, 42 105 polymorphisms were available for analyses. Univariate and bivariate animal models, using Bayesian approach via the Gibbs sampling algorithm, were used to estimate genetic parameters, benefiting from both genotypes and pedigree data.Key results The heritabilities for body-conformation traits ranged from a low of 0.08 +/- 0.04 to a medium value of 0.35 +/- 0.07, and the heritability for milk production was 0.23 +/- 0.01. We identified unfavourable genetic correlations between milk yield and udder depth (0.63 +/- 0.11) as well as body height (0.31 +/- 0.13). In contrast, there was a favourable genetic correlation between milk yield and rear udder width (0.61 +/- 0.14).Conclusion The heritability estimates confirmed the possibility of selecting animals for milk yield and body conformation traits related to the frame and mammary system categories. Based on the estimated genetic correlations, considerable importance should be given to the emphasis on selection for increased milk yield, because in the long term, this may promote undesirable changes in some type traits as body height and udder depth.Implications This information is relevant to selective breeding of Gir to enhance tropical milk production. Body-conformation traits in dairy cattle have been associated with health, welfare, and cow longevity, thus affecting herd productivity. The heritability estimates of this study indicated that body-conformations traits could respond to selection. Moreover, the correlations between these traits and milk yield highlighted the importance of considering the correlated response to selection, synergies, and trade-offs between body conformation traits and milk production in Gir cattle. This information is relevant for selective breeding in Gir cattle to enhance tropical milk production.