Background: The study of molecular processes regulating heat stress response in dairy cattle is paramount for devel-oping mitigation strategies to improve heat tolerance and animal welfare. Therefore, we aimed to identify quantitative trait loci (QTL) regions associated with three physiological indicators of heat stress response in Holstein cattle, includ-ing rectal temperature (RT), respiration rate score (RS), and drooling score (DS). We estimated genetic parameters for all three traits. Subsequently, a weighted single-step genome-wide association study (WssGWAS) was performed based on 3200 genotypes, 151,486 phenotypic records, and 38,101 animals in the pedigree file. The candidate genes located within the identified QTL regions were further investigated through RNA sequencing (RNA-seq) analyses of blood samples for four cows collected in April (non-heat stress group) and four cows collected in July (heat stress group). Results: The heritability estimates for RT, RS, and DS were 0.06, 0.04, and 0.03, respectively. Fourteen, 19, and 20 genomic regions explained 2.94％, 3.74％, and 4.01％ of the total additive genetic variance of RT, RS, and DS, respec-tively. Most of these genomic regions are located in the Bos taurus autosome (BTA) BTA3, BTA6, BTA8, BTA12, BTA14, BTA21, and BTA24. No genomic regions overlapped between the three indicators of heat stress, indicating the polygenic nature of heat tolerance and the complementary mechanisms involved in heat stress response. For the RNA-seq analyses, 2627 genes were significantly upregulated and 369 downregulated in the heat stress group in comparison to the control group. When integrating the WssGWAS, RNA-seq results, and existing literature, the key candidate genes associated with physiological indicators of heat stress in Holstein cattle are: PMAIP1, SBK1, TMEM33, GATB, CHORDC1, RTN4IP1, and BTBD7. Conclusions: Physiological indicators of heat stress are heritable and can be improved through direct selection. Fifty-three QTL regions associated with heat stress indicators confirm the polygenic nature and complex genetic determin-ism of heat tolerance in dairy cattle. The identified candidate genes will contribute for optimizing genomic evaluation models by assigning higher weights to genetic markers located in these regions as well as to the design of SNP panels containing polymorphisms located within these candidate genes.

Hanpeng Luo;Lirong Hu;Luiz F.Brito;Jinhuan Dou;Abdul Sammad;Yao Chang;Longgang Ma;Gang Guo;Lin Liu;Liwei Zhai;Qing Xu;Yachun Wang

Laboratory of Animal Genetics,Breeding and Reproduction,Ministry of Agriculture of China,National Engineering Laboratory of Animal Breeding,College of Animal Science and Technology,China Agricultural University,No.2,Yuanmingyuanxi Road,Haidian District,Beijing 100193,China;Department of Animal Sciences,Purdue University,West Lafayette,IN 47907,USA;College of Animal Science and Technology,Beijing University of Agriculture,Beijing 100096,China;College of Animal Science,Xinjiang Agricultural University,Urumqi 830052,China;Beijing Sunlon Livestock Development Company Limited,Beijing 100029,China;Beijing Dairy Cattle Center,Beijing 100192,China;College of Life Sciences and Bioengineering,Beijing Jiaotong University,Beijing 100044,China

畜牧与生物技术杂志（英文版）

[1]Hanpeng Luo;Lirong Hu;Luiz F.Brito;Jinhuan Dou;Abdul Sammad;Yao Chang;Longgang Ma;Gang Guo;Lin Liu;Liwei Zhai;Qing Xu;Yachun Wang-.Weighted single-step GWAS andRNA sequencing reveals key candidate genes associated withphysiological indicators ofheat stress inHolstein cattle)[J].畜牧与生物技术杂志（英文版）,2022(06):1714-1726

andRNA,withphysiological,ofheat,inHolstein,drooling,WssGWAS,autosome,BTA3,BTA6,BTA8,BTA12,BTA14,BTA21,BTA24,PMAIP1,SBK1,TMEM33,GATB,CHORDC1,RTN4IP1,BTBD7

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