Genetic parameters for latent variables derived from factor analysis of morphological and gait traits in Mangalarga Marchador horses

Our aim was to assess the reduction of computational demand compared to traditional multivariate analyzes, as well as identify latent variables with biological relevance (pseudo-phenotypes) through a factor analysis for morphological and gait traits in MM horses, estimating their genetic parameters within a Bayesian framework. A total of 15 morphological and performance traits were collected from 50,172 horses: withers height, croup height, thoracic perimeter, cannon bone perimeter, head length, neck length, back and loin length, croup length, shoulder length, body length, head width, croup width, morphofunctional points, gait and total points. The dataset was provided by the Brazilian Association of Mangalarga Marchador Horse Breeders (ABCCMM). A factor analysis was performed and six latent factors that explained 73 % of the total variance of the data were extracted. From them, four factors showed biological relevance, namely: "height" (F1), "gait ability" (F2), "robustness" (F3), and "head size" (F4), and were explored in the genetic analysis. The heritability estimates for F1 and F4 were of moderate to high magnitudes (0.47 ± 0.10 and 0.39 ± 0.10 for F1 and F4, respectively). The genetic correlations ranged from zero to high magnitudes, with notable values observed between F1 and F4 (0.80 ± 0.00), F1 and F3 (0.44 ± 0.01), and F3 and F4 (0.33 ± 0.01). The factor analysis proved to be an adequate alternative for reducing the dimensionality of variables and, consequently, the computational demand in the genetic evaluation of MM horses. Moderate heritabilities indicate the possibility of effective selection of horses based on these traits. In general, the correlations suggest that the selection of factors may result in genetic gains ranging from negative to high for other factors. Therefore, two factors are recommended to be used as selection criteria in MM horse breeding programs, which could contribute to the genetic improvement of the breed.