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Heat stress is a principal factor limiting production of animal protein in subtropical and tropical regions, and its impact is expected to increase dramatically. Development of effective strategies to improve the ability to cope with heat stress is imperative to enhance productivity of the livestock industry and secure global food supplies. However, selection focused on production and ignoring adaptability results in beef animals with greater metabolic heat production and increased sensitivity to heat stress. The goal of this research is to describe novel traits which can be used to characterize genetic pathways for thermotolerance which are independent or positively associated with production performance. Variance components, heritabilities, additive genetic correlations, and phenotypic correlations were estimated for skin histology characteristics, hair characteristics, body temperature under high temperature-humidity index (THI) conditions, and ultrasound carcass traits on 330 heifers from the University of Florida multibreed herd. A high heritability of 0.69 was estimated for the sweat gland area. The heritability for body temperature under high THI conditions was estimated to be 0.13 which is similar the heritability estimated reported for rectal temperature in a Brahman x Angus crossbred population (0.19; Riley et al., 2012) and dairy cattle (0.17; Dikmen at al., 2012). Sweat gland area had a negative genetic correlation with sweat gland depth (-0.49), short and long hair length (-0.45 and -0.28, respectively), and body temperature under high THI conditions (-0.65). These negative correlations suggest a similarity in the genetic control underlying these traits which would allow for selection of animals with large sweat glands, short hair (both topcoat and under coat), and able to maintain a lower body temperature under high THI conditions. More importantly, although weak, the genetic correlations between sweat gland area and the two production traits (backfat and intramuscular fat) were favorable (0.22 and 0.20, respectively).

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.

Heat stress in cattle has recently received growing attention because of anticipated increases in environmental temperature by global warming. Heat stress limits the production efficiency of cattle, and it is one of the principal causes of economic loss for beef cattle producers in these environments. Thermotolerance can be defined as the ability to maintain optimal growth, feed intake, and reproduction under the presence of heat stress, and it varies among individual animals and breeds. The objectives of the analysis were to investigate the amount of variation on epidermis thickness, test the effect of breed composition and age group on skin histology traits and to conduct a genome-wide association study on skin properties of beef cattle, focusing on the epidermis thickness. Skin biopsy samples were collected from 318 heifers from a UF multibreed population (animals ranging from 100% Brahman to 100% Angus), genotyped with the Bovine GGP F250K chip. Quality control was conducted with BLUPF90 software, including a call rate of 0.90 and a MAF < 0.01. BLUPF90 software was used to fit a single locus mixed model to test the effect of each marker. Breed group and age group were included as fixed effects. There is a significant effect in breed group ((P < 0.0001) and in age group (P < 0.0001). This study shows there is a large amount of variation in epidermis thickness across and within breed groups. Significant SNPs for the thickness of the epidermis were found in the HBEGF gene, which is a protein coding involved in several processes, including epidermal growth factor receptor signaling pathway and there is a variation across breed Skin histology traits are fundamental for the ability to lose heat more efficiently and allow the maintenance of normal body temperatures under extreme conditions. This study could contribute toward improving cattle’s adaptation to thermal stress.