A reaction norm model approach to estimate the genetic effect of temperature on sportive performance of trotter horses.

The study explores the impact of temperature on the performance of Spanish Trotter Horses during races, finding that their speed is best in temperatures between 4°C and 12°C and decreases in hotter weather. The research also found evidence of a genetic influence over these temperature-related performance changes.

Objective and Methodology

• This study investigates the genetic effect of temperature on the sportive performance of trotter horses.
• The researchers conducted the study by merging race performance results of Spanish Trotter Horses with the temperature data from the nearest official weather stations at the time of the races.
• The data used in the study comprised 104,125 individual results from 7,653 races featuring 3,772 horses and driven by 1,402 jockeys.
• The researchers used a classical repeatability animal model in the initial stages and then adopted random regression models (RRM) to estimate the effect of temperature on the race’s speed.

Findings

• The study determined that horses perform best when temperatures rise from 4°C to 12°C, entering what the researchers described as a ‘comfort zone’ between 12°C and 19°C.
• Performance slightly decreases in what the study refers to as a ‘light but more stressful zone’, which is above 20°C.
• There was a significant change in temperature of +4°C over a 20-year period while the speed of the race improved by +2.1 m/s during the same time-span.
• LogL, AIC and BIC information criterion indicated the presence of heterogeneity of (co)variance components along the temperature scale.
• The model that assumed a non-constant effect of temperature across the temperature scale for animal genetic effects, the individual environmental permanent effects, and the jockey effects fit the data better.
• The study showed higher values of heritability (0.19-0.20) when the temperature was below 12°C and slightly decreases within the comfort and stressful zones.

Implications

• Genetic correlations were observed to decrease when the difference in temperature increased. This suggests a genetic basis for the way horses’ performances vary with temperature.
• By using the Expected Breeding Value (EBV) estimated with the best RRM, the best 150 horses for speed during the ‘comfort zone’ were selected, with noticeable variations detected in the evolution of EBV across the temperature trajectory.