Genome-wide association studies for heat stress response in Bos taurus x Bos indicus crossbred cattle

Heat stress is an important issue in the global dairy industry. In tropical areas, an alternative to overcome heat stress is the use of crossbred animals or synthetic breeds, such as the Girolando. In this study, we performed a genome-wide association study (GWAS) and post-GWAS analyses for heat stress in an experimental Gir x Holstein F-2 population. Rectal temperature (RT) was measured in heat-stressed F-2 animals, and the variation between 2 consecutive RT measurements (Delta RT) was used as the dependent variable. Illumina BovineSNP50v1 BeadChip (Illumina Inc., San Diego, CA) and single-SNP approach were used for GWAS. Post-GWAS analyses were performed by gene ontology terms enrichment and gene-transcription factor (TF) networks, generated from enriched TF. The breed origin of marker alleles in the F-2 population was assigned using the breed of origin of alleles (BOA) approach. Heritability and repeatability estimates (+/- standard error) for Delta RT were 0.13 +/- 0.08 and 0.29 +/- 0.06, respectively. Association analysis revealed 6 SNP significantly associated with Delta RT. Genes involved with biological processes in response to heat stress effects (LIF, OSM, TXNRD2, and DGCR8) were identified as putative candidate genes. After performing the BOA approach, the 10% of F-2 animals with the lowest breeding values for Delta RT were classified as low-Delta RT, and the 10% with the highest breeding values for Delta RT were classified as high-Delta RT. On average, 49.4% of low-Delta RT animals had 2 alleles from the Holstein breed (HH), and 39% had both alleles from the Gir breed (GG). In high-Delta RT animals, the average proportion of animals for HH and GG were 1.4 and 50.2%, respectively. This study allowed the identification of candidate genes for Delta RT in Gir x Holstein crossbred animals. According to the BOA approach, Holstein breed alleles could be associated with better response to heat stress effects, which could be explained by the fact that Holstein animals are more affected by heat stress than Gir animals and thus require a genetic architecture to defend the body from the deleterious effects of heat stress. Future studies can provide further knowledge to uncover the genetic architecture underlying heat stress in crossbred cattle.