Impact of reproductive biotechnologies on genetic variability of Argentine Polo horses

The Argentine Polo Horse (AP), an autochthonous breed officially created in Argentina in the early 1980s, is globally recognized as the best equid for playing polo. Their breeding is characterized by the use of cutting-edge assisted reproductive techniques such as large-scale embryo transfer (ET) programs and cloning. The aim of this study was to determine the impact of the use of those reproductive biotechnologies on the genetic structure, variability and reproductive parameters of the AP breed using genealogical data (81,633 pedigree records). In total, 18,077 animals drawn from the last generation (2006-2015) were employed as the reference population (WP), which was further divided into two subsets: animals produced (ET; n = 13,478) and not produced by ET (NOT-ET; n = 4,599). Horses produced by ET showed a significant decrease in generation interval compared with NOT-ET. On the other hand, the number of foals per stallion and broodmare as well as inbreeding (F = 0.89%) and average relatedness (AR=1%) were higher in ET compared with NOT-ET (F = 0.6%; AR = 0.54%), depicting an increased selective intensity. Our analysis also revealed that the effective number of founders and ancestors in ET showed a disproportionate gene contribution and a strong genetic bottleneck as well as the inter-herd fixation index (F-ST) revealed an increased genetic flow among herds and higher internal relatedness values within ET horses. In conclusion, the use of large-scale ET programs decreased genetic variability (lower effective population size and number of founders and ancestors and higher F, AR and coancestry), increased the genetic flow among herds and decreased the generation interval, contributing to the possibility of higher rates of genetic progress in the AP.