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

Objective Overview

• This study explores how the economic scale of barrel racing events, represented by prize money, influences the genetic and environmental factors affecting race times in Brazilian Quarter Horses.
• It aims to determine whether differences in prize money correspond to changes in the genetic variance and other components contributing to performance variability in these horses.

Background and Rationale

• Barrel racing performance is determined by multiple factors including:
• Genetic merit of the horses
• Rider ability and strategy
• Training methods
• Specific conditions of each competition
• Events vary widely in the amount of prize money offered, which is thought to reflect differences in:
• Management intensity (how meticulously the horses are managed)
• Rider expertise (more money may attract better riders)
• Selection pressure (more competitive and selective environments)
• By using total prize money as a proxy for these factors, researchers can examine how environmental gradients affect genetic and non-genetic components of performance.

Methods

• The study analyzed 349,262 race records from Brazilian Quarter Horses participating in barrel racing.
• A reaction-norm model was used, which allows examination of how genetic and environmental effects change continuously across a gradient — here, the prize money per event.
• Three main random effects were included in the model, each allowed to vary along the prize money gradient:
• Genetic effects (additive genetic variance)
• Permanent environmental effects (consistent environmental influences on individual horses)
• Rider effects (contributions of individual riders to performance)
• Variance components were estimated for different points on the prize money gradient to see how variability changes with economic conditions.
• Genetic correlations between environments of different economic scales were calculated to evaluate whether different prize-money levels lead to changes in genetic rankings of horses (genotype-by-environment interaction).

Results

• Additive Genetic Variance: Showed a moderate increase from 7.78 to 8.46 as prize money increased, indicating genetics play a slightly larger role under high-prize conditions.
• Rider and Permanent Environmental Variance: Both increased more substantially at higher prize money levels, with rider effects explaining up to 29% of phenotypic variance in the highest prize categories.
• Residual Variance: Decreased markedly from about 17.36 to 10.19 with increasing prize money, implying competition outcomes became more consistent and less noisy at elite-level events.
• Heritability: Ranged between 0.19 and 0.23 across the prize-money gradient, suggesting a relatively stable proportion of performance variability attributable to genetics.
• Genetic Correlations: High correlations (>0.90) between low and high prize environments indicate limited genotype re-ranking; horses performing well genetically in one environment tend to do so in others.
• Rider and Environmental Correlations: These correlations declined to approximately 0.93-0.83 between contrasting environments, showing that non-genetic factors are more environment-specific.

Conclusions

• Prize money successfully captures important environmental variation influencing barrel racing performance.
• Changes across prize money levels mainly affect non-genetic factors, particularly rider skill and management conditions.
• Genetic effects exhibit limited plasticity across economic conditions with minimal evidence of genotype-by-environment interaction; horses retain their relative genetic merit regardless of prize money class.
• This suggests that selection for genetic improvement can be effective across different competition levels, but optimizing rider and management practices is crucial to enhancing performance especially in elite competitions.