Microevolution operating in domestic animals: evidence from the Colombian Paso horses

Colombian Paso horses have been classified into four categories based on gait performance: Colombian Paso Fino, Colombian Trocha, Colombian Trocha and Gallop, and Colombian Trot and Gallop. Selective breeding has led to the emergence of the Colombian Paso Fino as a distinct population. We describe the split of the Colombian Paso Horse breed into two genetic and phenotypic differentiated groups using 220,000 pedigree records, 132,637 microsatellites genotypes, 198 mtDNA d-loop haplotypes, and several conformation measurements from 178 horses. The first category, the Colombian Paso Fino subgroup was recognized as a new breed by the Colombian breeders and government since 2017 and the second category consists of the other three subgroups of Colombian Paso horses that perform different gaits and have different conformation traits. The breed splitting has been carried out through increased genetic differentiation between these two populations, mainly by intensive artificial selection on gaits and some anatomical conformation traits related to performance and is revealed by analysis of 30 years of traced genetic data, 60 years of pedigree records, and phenotypic differences. In addition, our phylogenetic reconstruction showed that the Colombian Paso horses have shared an evolutionary history that led to a complex breed origin. Some haplotypes represent an old Iberian haplogroup, even older than the domestication of horses. Finally, this study shows support for the designation of a distinct breed based on the use of genetic information as scientific support to breeding associations and governments for decision making about breeding management, genetic conservation, and genetic improvement.