H. Asadollahi - Department of Animal Science, Faculty of Agriculture, Tarbiat Modares University, Tehran, Islamic Republic of Iran.
R. Vaez Torshizi - Department of Animal Science, Faculty of Agriculture, Tarbiat Modares University, Tehran, Islamic Republic of Iran.
A. Ehsani - Department of Animal Science, Faculty of Agriculture, Tarbiat Modares University, Tehran, Islamic Republic of Iran.
A. Masoudi - Department of Animal Science, Faculty of Agriculture, Tarbiat Modares University, Tehran, Islamic Republic of Iran.

Heat stress, or hyperthermia, can have a serious effect on chicken performance in poultry industry in many parts of the world. Both genetics and environment play key role in the performance of a chicken and, therefore, it is important to consider both factors in addressing heat stress. On genetics level, genome-wide association studies have become a popular method for studying heat stress in recent years. A population of ۲۰۲ F۲ chickens was reared for ۸۴ days to find genes and genomic regions affecting growth traits and immune system. But, due to unexpected acute increase in temperature at day ۸۳, ۱۸۲ birds died (case) and ۲۰ birds remained alive (control). At the age of ۷۰ days, blood sample of all birds was collected to extract their DNA, using modified salting out method. All samples were genotyped by a ۶۰ K Single Nucleotide Polymorphism (SNP) chip. Genome-wide association study was carried out by GCTA to identify gene and genomic regions associated with heat stress tolerance. Results indicated a close relationship between ۲۸ SNPs, located on chromosomes ۲, ۳, ۵, ۶, ۷, ۱۲, ۱۹, ۲۰, and ۲۱ and heat stress tolerance at the level of suggestive significance. Two suggestively significant markers on chromosome ۵, namely, GGaluGA۲۷۳۳۵۶ and Gga_rs۱۶۴۷۹۴۲۹, were located within and ۵۲ Kb downstream of two genes, including MAPKBP۱and SPON۱, respectively. Gene ontology analysis indicated that the resistance of chickens to acute increase of temperature might be linked to the function of MAPKBP۱ and SPON۱ genes and their biological pathways. These results will be useful for understanding the molecular mechanisms of SNPs and candidate genes for heat stress tolerance in chickens and provide a basis for increasing genetic resistance in breeding programs.

Gene ontology analysis, GWAS, Hyperthermia, Single nucleotide polymorphism.