Thermal Thresholds and Genetic Sensitivity in Barrel Racing Performance of Quarter Horses Across Temperature–Humidity Indices

Description

Mário Luiz Santana and Annaiza Braga Bignardi asked at what heat load barrel racing horses start losing speed, and whether some bloodlines tolerate heat genetically better than others. Their 2026 study analyzed 351,993 race times from 13,960 Brazilian Quarter Horses against two heat indices combining temperature and humidity. It used segmented regression to find breaking points and genetic models that estimate how performance sensitivity to heat is inherited.

Both indices showed clear thresholds: performance deteriorated faster beyond a temperature humidity index of 74.7 and a wet bulb globe temperature of 23.6 in the fitted models. By those cutoffs, 31.15 percent and 20.71 percent of race events respectively had run under heat stress conditions, making the problem routine rather than rare. Genetic analyses separated baseline speed from heat sensitivity as distinct, selectable traits. Breeders can select for thermal robustness without abandoning speed, the authors argue.

Catalog record

Source: https://europepmc.org/articles/PMC13460854