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In subtropical and tropical environments, beef cattle production faces significant challenges due to heat stress, affecting animal welfare and productivity. To mitigate these effects, producers have turned to crossbreeding and the development of composite breeds like Brangus, which combine the desirable carcass and meat quality traits of European taurine cattle with the thermotolerance of Indicine breeds. However, the genetic underpinnings of thermotolerance in these composite populations are not well understood, owing to the complex nature of measuring related traits and the genetic intricacies arising from crosses of distinct populations. This study aims to identify key quantitative trait loci (QTL) related to thermotolerance, employing an approach that integrates genetic markers alongside the marker’s breed of origin of alleles (BOA) in Brangus heifers. Data were collected on histological sweat gland area (SWA), hair length (HL), and thermal stress slope as a measure of the increase in body temperature from a low to a high temperature-humidity index (TSS), from 2,233 Brangus heifers genotyped with the 250K functional chip. BOA was determined using LAMP-LD software, using Angus and Brahman cattle from the University of Florida’s multibreed Angus-Brahman project as a reference population. We conducted a genome-wide association study (GWAS) incorporating BOA-specific effects, revealing several genes with BOA-specific effects. Notably, the CGGBP1 gene exhibited a significant effect on TSS only when alleles originated from Brahman. Conversely, the PLK1 gene was significant for TSS when alleles originated from Angus. Both CGGBP1 and PLK1 interact with heat shock proteins during heat stress, these findings reveal different genetic mechanisms for controlling internal body temperature. For HL, a significant Brahman-specific effect was found near the PRLR gene, which is known as the gene controlling the SLICK hair phenotype in Criollo cattle. For SWA, an Angus-specific significant association was found with the PDE4D gene. PDE4D interacts with the cAMP pathway which regulates sweat gland growth and sweat production. These findings underline the genetic complexity of thermotolerance in composite cattle and the crucial role of BOA in identifying key QTL. The study offers novel insights into the genetic mechanisms of thermotolerance, providing a foundation for breeding strategies aimed at improving heat resilience in cattle in subtropical and tropical environments. [ABSTRACT FROM AUTHOR]

More than one-half of the world’s cattle are maintained in hot environments, making heat stress a significant issue for the beef industry. Around $370 million is lost annually due to reduced performance due to heat stress, which has other detrimental impacts on cattle, such as decreased feed intake, fertility, and immune response. The assessment of hair glucocorticoids (hGC) serves as a valuable tool for evaluating chronic stress levels in beef cattle. Unlike traditional cortisol measurements, which provide only a glimpse of stress at a specific moment, hGCs offer a retrospective view of long-term stress exposure. This makes them particularly valuable for assessing chronic stress, which can profoundly impact animal health, welfare, and productivity. By quantifying hGC concentrations, we gain insights into the cumulative stress experienced by cattle over time, allowing for more comprehensive monitoring and management strategies. This study investigated the relationship between hGC concentrations and breed composition in beef cattle, specifically focusing on whether breed composition influences hGC concentrations after prolonged heat exposure. Animals from the University of Florida’s Multibreed Angus-Brahman herd were used. Hair samples were collected from 240 cows during the summer of 2017 and 2018, with breed compositions ranging from 100% Brahman to 100% Angus. Starting with a 4 mg hair sample, the hGC were extracted and analyzed with the Cortisol ELISA KIT (Neogen Corporation, Ayr, UK). An Analysis of Variance (ANOVA) was conducted to examine the relationship between hGC concentration, breed composition, and batch effect. The results indicated a significant effect of breed composition on hGC concentration (P-value 0.01406). These findings suggest that breed composition influences chronic stress during prolonged periods of heat exposure. However, individual factors like thermotolerance, health status, and social stress may also have a role in chronic stress levels. To better understand these factors, future steps will involve comparing the hGC concentration results between thermotolerant and non-thermotolerant animals. This comparison will provide insights into the potential differences in stress responses between cattle breeds adapted to hot environments and those less tolerant to heat stress. [ABSTRACT FROM AUTHOR]

Heterosis is the tendency of crossbreed animals performing better than the average of the purebred parents. Heterosis retention is essential in crossbreeding and composite breeding systems. However, not every genomic region benefits from heterosis, with certain traits showing an improvement when certain genomic regions are kept fixed for a certain breed. The objectives of this study were to detect such regions in a commercial Brangus herd, using genotypes, and Breed of Origin (BO) genotypes to identify runs of homozygosity (ROH) and investigate their effects on meat traits. The Brangus herd was genotyped with the Bovine GGP F250 array, after quality control, 99,669 variants, and 1,046 cattle remained. These genotypes were converted into BO genotypes with LAMP-LD, which describes the origin of the markers either from Angus or Brahman ancestry. The new BO genotypes and original genotypes were then used to identify ROH using the -homozyg function PLINK. The ROH genotypes were fit into a single locus mixed model for hot carcass weight (HCW) and marbling (MARB) using the EMMAX procedures in Golden Helix. The same single locus mixed model was used on both genotypes and Breed of Origin genotypes using the EMMAX procedures in Golden Helix. Using BO alleles, and ROH alongside traditional genotypes can help identify regions with significant effects on carcass traits. Providing important information for crossbreeding/composite breed systems about regions which should remain fixed for breeds. [ABSTRACT FROM AUTHOR]

Thermal stress in subtropical regions is a major limiting factor in beef cattle productions with around $370 million being lost annually due to reduced performance. About 45% of beef cattle in the United States are in the southern and southeastern states where tropical and subtropical climates are most prevalent. Cattle utilize sweating to dispense most of their excess heat allowing them to return to their thermoneutral zone. The objective of this study was to conduct a genome-wide association study on sweat gland area in the Multi-breed Angus-Brahman herd of the University of Florida. Skin samples were collected along the shoulder from 337 cows of varying Brahman and Angus percentages. Cows were genotyped with the Bovine GGP F250k array. The biopsies were processed into histology slides and then ImageJ software was used to measure sweat gland area. A general linear model was used to test the significance of breed composition and age group on sweat gland area. Breed composition and age group had a significant effect on sweat gland area (P < 0.0001 and P < 0.0001, respectively), with sweat gland area increasing with Brahman percentage. Quality control was conducted using BLUPF90 software including a call rate of 0.90 and a minor allele frequency of 0.01 which left 125,035 SNPs available for the single-step genome wide association analysis. BLUPF90 software was used to fit a single locus mixed model to test the effect of each marker. There were a significant SNPs located in the MINDY1 and PRUNE1 gene, which are involved in cell proliferation and induction of cell motility. These results show that with selection on these SNPs, can improve the ability of cattle to adapt to thermal stress. [ABSTRACT FROM AUTHOR]

This study evaluated the effectiveness of genetic introgression of the SLICK1 allele derived from Senepol cattle into the Holstein breed to enhance thermotolerance. The SLICK1 allele, located in PRLR gene, confers a short and sleek coat that is inherited as a simple dominant phenotype. Approximately 40 years ago, the University of Florida initiated efforts to introgress this allele into the Holstein population. Here we tracked the introgression of the SLICK1 allele using a medium-density genotyping array and a reference population of both breeds (50 Holstein, 46 Senepol). Among the 31 SLICK1+ Holsteins, there was 15.25% ± 11.11% (mean ± SD) Senepol ancestry on BTA20. Holsteins at the University of Florida descended from slick matings that did not inherit the SLICK1 allele (n=9) exhibited no Senepol ancestry. A secondary introgression of Senepol genetics in SLICK1+ animals was found on BTA4, spanning 54 markers and 15 genes, with 26.67% Senepol ancestry. This region, previously linked to heat stress adaptation, suggests that the introgression extends beyond the SLICK1 allele to incorporate additional beneficial genetics for thermal stress adaptation. These findings indicate that deliberate introgression of the SLICK1 allele enhances specific traits and potentially introduces other adaptive genetic variations. The study demonstrates the successful use of genetic interventions to improve livestock resilience against environmental challenges without significantly disrupting the recipient breed's genetic structure. The introgression of the SLICK1 allele serves as a model for breeding programs aimed at optimizing animal welfare and productivity in the face of global climate change while maintaining breed integrity., (© The Author(s) 2024. Published by Oxford University Press on behalf of The American Genetic Association. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)