Long term effect of large-scale embryo transfer programs in the genetic structure and variability of Argentinean Polo horses: a 30 years retrospective

AZCONA FLORENCIA; MOLINA ANTONIO; PIROSANTO YAMILA; VALERA, M.; PERAL-GARCÍA, P.; TRIGO, P.; DEMYRA-PEYRAS SEBASTIAN

Pisa

Congreso; International Symposium on Equine Embryo Transfer and Technologi; 2021

Argentinean Polo horse (AP) is a novel breed created by selecting crossbred individuals based on their performance in the polo game during the last four decades. Originally, most individuals were produced by mating Thoroughbred stallions with native Argentinean mares characterized by their sporting ability. However, during the last 30 years, matings were mostly between individuals of the Argentinean Polo breed, but also by the development of large-scale ET programs. Despite that such assisted reproductive technologies were associated with changes in the genetic structure of livestock populations (Azcona et al. Livestock Science. 2020, 231: 103848), long-term analysis of its effect in a horse breed is still absent. Therefore, we analyzed the effect of the massive use of ET on 6 genetic population parameters in the Argentinean Polo horse during the last 30 years. To this end, 56924 foaling records reported between 1987 and 2016 obtained from Argentinean Polo Horse stud book public data base were clustered in periods of five years for the analysis (Table 1). The percentage of ET produced horses (ET%), average relatedness (AR), the effective number of founders (Fe) and ancestors (Fa), and effective population size (via individual increase in inbreeding, Ne) were estimated in each period of time, using ENDOG package. Statistically significant differences in AR and ET% between groups, according to year of birth, were estimated by ANOVA and post-hoc LSD test. Finally, correlations between ET% and those parameters were calculated. Our results show a steady increase in the use of ET over the years, accounting for more than 50% of the foals born during the last decade analyzed. We also demonstrated a parallel reduction in the variability and genetic base of the population (with correlations close to -1 observed between ET% and Fe and Fa) but also an increased relatedness (Table 1), as well as a increasing genetic bottleneck shown by the increase of the Fe/Fa ratio in correlation with ET%. All these changes were particularly singifying during the last 15 years when ET% accounted for more than 30% of the foals. Despite that there is no phenotypic data, our results strongly suggest that the ET programs are responsible for the increased selection process towards the sport phenotype observed during the last 15 years in the Argentinean Polo horse. Table 1.Year of birthTotal FoalsET foals%ETARFeFaFe/FaNe1987-19915800230.40% a0.03% a10179691.0371.21992-199650832274.47% a0.07% b9307641.2262.251997-2001619198415.89% b0.15% c10106191.6230.52002-200611750339928.93% c0.25% d10394292.4214.932007-201118379990853.91% d0.50% e7181464.9247.682012-20169721628664.66% e0.79% f363527.0226.48Correlation with %ET0.9773**-0.8461*-0.9844**0.9729 **-0.5741** P