The influence of foreign lineages in the genetic component of reproductive traits in Criollo Argentino mares: A 30-year study

The Criollo horse is the most important equine breed in Argentina. These horses are characterized by their strength, resistance, and increased fertility even at old ages, and they are also associated with Argentine tradition and livestock heritage. However, over the last 70 years, the Criollo Argentino breed has been influenced by other South American Criollo horses from Brazil, Uruguay, or Chile. In this study, we aimed to determine the genetic influence of foreign individuals on the reproductive performance of Criollo Argentino mares. To achieve this, we analyzed a large dataset including pedigree records of nearly 212,000 individuals. For the analysis, the in-dividuals were organised into clusters based on their genetic origin (foreign or native Criollos). We then per-formed a comprehensive genetic characterization of each group, as well as an estimation of the estimated breeding values (EBVs), heritabilities, and genetic correlations for the three traits, using a multi-trait mixed model. Our results demonstrate a positive trend toward the introgression of foreign breeding lineages in the Criollo Argentino population. However, we also quantified a low-to-moderate genetic influence on all the fertility traits analysed, and the absence of any negative effect associated with inbreeding. Despite the fact that the genetic origin produced certain differences between foreign and native individuals in terms of fertility at the beginning of the study, the use of foreign lineages did not significantly change the fertility of the Criollo Argentino mares. To our knowledge, this is the first study analysing the fertility of Criollo horses from a genetic point of view.