Disease & heat resistance

Thermal Stress Slope: A Novel Heritable Trait for Genetic Selection of Heat-Tolerant Beef Cattle

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Abstract

Heat stress compromises beef cattle health, growth, and reproduction, with significantly costs to the beef industry. As global temperatures rise and the demand for beef increases, selecting for thermotolerance alongside production traits is vital for food security; however, current indicators of thermotolerance - such as reaction norm slopes - are often limited by environmental noise and low heritability. The objective of this study was to identify a measurable and more heritable indicator of thermotolerance by evaluating noise-reduction methods and novel mathematical models of heat stress response. The study utilized 207 heifers from a multibreed Angus-Brahman population. Body temperature and temperature-humidity index (THI) were recorded at 15-min intervals. Three noise reduction methods were tested, time-series decomposition was performed, and cross-correlation between the time-series were calculated to explore the association between THI and body temperature. Reaction norm slopes from linear mixed models were used as thermotolerance indicators. Additionally, change in THI/body temperature and area under the curve were used as indicators of resistance to heat stress. Square root, natural log, and cube root transformations were applied to improve model fit, resulting in eight equations tested as thermotolerance indicators. Heritability and repeatability of these indicators were estimated to determine the most suitable metric. Cross-correlation analysis with raw data indicated that body temperature lagged behind THI by 1 hour in Angus and 5 hours in Brahman. However, after removing 24-hour diurnal cycles via time-series decomposition, this lag disappeared, indicating that the apparent delay was an artifact of confounding diurnal rhythms rather than a physiological response. Heritability estimates for reaction norm slopes ranged from 0.07 to 0.12 and were similar before and after noise reduction, time-series decomposition, and lag correction, suggesting that nonlinearity in the relationship between body temperature and THI had minimal impact on reaction norm slope estimates. In contrast, heritability estimates for the eight thermotolerance indicator equations ranged from 0.20 to 0.55 with repeatability ranging from 0.20 to 0.74. Among the evaluated approaches, the Thermal Stress Slope (TSS) provided the most precise and consistent metric across days. This finding is particularly relevant for the genetic improvement of heat-stress resilience in beef cattle, as TSS combines high heritability with consistent measurements across time, enabling more effective selection for thermotolerance. This study developed and evaluated novel metrics to quantify thermotolerance in beef cattle based on the relationship between body temperature and environmental heat load. Overall, TSS offers a biologically meaningful and genetically tractable indicator of thermotolerance that can enhance the identification and selection of heat-resilient animals, contributing to the long-term sustainability and productivity of beef cattle in hot and humid environments.

Keywords: 2026

How to Cite:

Rodriguez, E., Zayas, G., Rezende, F. & Mateescu, R., (2026) “Thermal Stress Slope: A Novel Heritable Trait for Genetic Selection of Heat-Tolerant Beef Cattle”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2343759. doi: https://doi.org/10.31274/wcgalp.24485

Rights: 1