When genes meet money: Genotype-by-prize interaction in Quarter Horses

Barrel racing performance reflects a complex interplay among genetic merit, rider ability, training strategies, and competition-specific conditions. In practice, events differ substantially in their economic scale, and prize money can serve as a proxy for management intensity, rider expertise, and selection pressure.

This study investigated whether economic stratification, represented by total prize money per event, is associated with changes in (co)variance components for barrel racing time in Brazilian Quarter Horses.

A reaction-norm model was implemented using 349,262 race records, with genetic, permanent environmental, and rider effects modeled as random regressions along a continuous prize-money gradient. Variance components and genetic parameters were estimated across the gradient, and heterogeneity was assessed by comparing variance trajectories and correlation structures between contrasting economic environments.

Additive genetic variance increased moderately along the gradient (7.78 to 8.46), whereas rider and permanent environmental variances showed more pronounced increases, particularly in high-prize events. Residual variance declined from approximately 17.36 to 10.19, indicating greater homogeneity under elite conditions. Heritability estimates ranged from 0.19 to 0.23 across the gradient. Genetic correlations between low- and high-prize environments remained high (>0.90), whereas rider and permanent environmental correlations decreased to ∼0.93-0.83, evidencing stronger environmental specificity of non-genetic effects. Rider effects accounted for up to 29% of phenotypic variance in high-prize classes.

Prize money effectively captures an environmental gradient influencing variance heterogeneity. However, performance plasticity across economic contexts is primarily driven by rider and management effects, with limited evidence of genotype re-ranking.