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Thermal Thresholds and Genetic Sensitivity in Barrel Racing Performance of Quarter Horses Across Temperature-Humidity
Mário Luiz Santana1, Annaiza Braga Bignardi1
1Grupo de Melhoramento Animal de Mato Grosso (GMAT), Instituto de Ciências Agrárias e Tecnológicas, Universidade Federal de Rondonópolis (UFR), Rondonópolis, MT, Brazil.
Summary
Heat stress significantly impacts equine athletic performance. This study found that while genetic factors for barrel racing performance remain consistent across temperatures, selecting for heat tolerance can improve endurance in changing climates.
Area of Science:
- Animal Genetics
- Equine Science
- Environmental Physiology
Background:
- Heat stress poses a growing threat to equine athlete performance and welfare, especially in diverse climates.
- Understanding genetic responses to thermal load is crucial for effective genetic evaluations and sustainable breeding.
- Barrel racing performance in Brazilian Quarter Horses is susceptible to environmental thermal conditions.
Purpose of the Study:
- To assess barrel racing performance in Brazilian Quarter Horses across varying thermal environments.
- To identify heat stress thresholds using the temperature-humidity index (THI) and wet bulb globe temperature (WBGT).
- To estimate genetic parameters for performance and environmental sensitivity in heat stress conditions.
Main Methods:
- Analysis of 351,993 barrel racing time records from 13,960 Quarter Horses.
- Application of segmented regression to identify heat stress thresholds (THI = 74.7, WBGT = 23.6).
- Utilized random regression models to estimate genetic parameters across thermal gradients.
Main Results:
- Performance declined more rapidly beyond identified heat stress thresholds.
- Heat stress affected 31.15% (THI) and 20.71% (WBGT) of events.
- Heritability decreased slightly under heat stress, but high genetic correlations indicated consistent performance rankings.
Conclusions:
- THI and WBGT provided consistent results for thresholds and genetic parameters.
- While WBGT is more sensitive in extreme heat, THI offers practical advantages.
- Selecting for genetic heat tolerance is recommended to maintain barrel racing performance amid climate change.
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