Exploring the Genetic Link Between Coat Colour and Morphological Traits: The Case of Peruano de Paso Horse

The Peruano de Paso is a horse breed renowned for its smooth gait, traditionally selected based on breeders' empirical knowledge. Recently, the frequency of chestnut horses, a recessive trait, has increased substantially within the official studbook. This study evaluated whether preference for chestnut coat colour has influenced morphological traits and genetic diversity within the breed. A total of 8376 records of seven morphological traits, collected by the Peruano de Paso Breeders Association over eight years, were analysed, along with a pedigree including 41,357 individuals. Morphological traits were studied through univariate genetic models that considered potential heterogeneity of additive genetic variance between chestnut and non-chestnut horses. Results indicated moderate to high heritability estimates across traits. No significant differences were observed between groups, except for croup width, with heritability of 0.28 ± 0.08 in chestnuts and 0.44 ± 0.08 in non-chestnuts. Genetic correlations between groups could not be precisely estimated due to limited data. The main effect of selection for chestnut coat colour was a reduction in genetic variability, an increase in inbreeding and relatedness. However, this selection has had little impact on morphology, indicating that the traits valued by breeders remain almost unaffected despite the loss of diversity.