Disease & heat resistance

Fine-Mapping Genomic Regions Contributing to Thermotolerance in Beef Cattle

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Abstract

Heat stress is a major constraint to beef production in tropical and subtropical regions, reducing animal welfare, fertility, and growth efficiency. The objective of this study was to identify and fine-map genetic loci contributing to thermotolerance in beef cattle. Data from 4,114 heifers were analyzed, including 3,545 Brangus from two commercial herds (2016-2019) and 569 heifers from the University of Florida multibreed Angus à— Brahman herd (2017-2024). Thermotolerance was characterized using a comprehensive set of traits describing both body temperature regulation and heat dissipation. These included internal body temperature traits (minimum and maximum vaginal temperature, temperature change relative to the thermal-humidity index, thermal stress slope, and reaction norm parameters), which exhibited low heritability (0.16-0.21), hair characteristics (coat score, topcoat length, undercoat length) with moderate heritability (0.27-0.41), and skin morphology traits related to sweat gland and dermal structure, which showed moderate heritability (0.27-0.46). All animals were genotyped using a 250K SNP array, and genome-wide association analyses were performed in GCTA using a mixed linear model with a leave-one-chromosome-out approach. Across all traits, 36 quantitative trait loci exceeded the Bonferroni-corrected significance threshold (α = 0.1). To fine-map these regions, whole-genome sequencing was conducted in 92 animals selected from phenotypic extremes for thermal stress slope, topcoat length, and sweat gland depth, defined as individuals in the upper and lower 25% of adjusted phenotypes. Phenotypic extremes were selected within purebred Angus (10 total), purebred Brahman (10 total) and commercial Brangus populations (72 total). Forward-selection fine-mapping and functional annotation were then applied to identify candidate variants and genes. Fine-mapping revealed loci with moderate to large effects on thermotolerance. On BTA1, SNP rs437400062 (effect = 1.02 SD, P = 7.2 à— 10⁻⁸) lies upstream of ZBTB20, a transcriptional regulator involved in metabolic and circadian control of thermogenesis. On BTA19, SNP rs381632699 (effect = 1.06 SD, P = 3.7 à— 10⁻⁶) is upstream of MAP3K14, which encodes NF-κB-inducing kinase and plays a role in hypothalamic and adipose thermoregulatory signaling. On BTA20, a 9-bp insertion/deletion at 35,820,858 bp (effect = 1.29 SD, P = 6.7 à— 10⁻12) upstream of RICTOR and a 6-bp deletion at 38,593,307 bp (effect = 1.51 SD, P = 1.3 à— 10⁻6) upstream of PRLR were associated with topcoat length. These findings identified biologically meaningful genetic variation underlying thermotolerance and heat dissipation, provide high-resolution insight into the genetic architecture of heat resilience, and highlight functional variants that can be incorporated into genomic evaluations as biologically informed markers to enhance selection for heat tolerance in beef cattle.

Keywords: 2026

How to Cite:

Zayas, G., Santos Rojas, C., Rodriguez, E. & Matescu, R., (2026) “Fine-Mapping Genomic Regions Contributing to Thermotolerance in Beef Cattle”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2283463. doi: https://doi.org/10.31274/wcgalp.23499

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