Genetic diversity and thermotolerance in Holstein cows: Pathway analysis and marker development using whole‐genome sequencing

Abstract

Heat stress causes extensive losses in the dairy sector, due to negative effects on milk production and reproduction. Cows have evolved a series of protective mechanisms, (physiological, biochemical, behavioural) to cope with the thermostressing environments, which have allowed the preservation of productive and reproductive potential of specific animals during summer; these animals are considered thermotolerant and could be used to design programs of selective breeding. These programs, targeting the generations of a population of heat‐resistant animals, would increase the frequency of the desired phenotypes, tackling the financial losses on one hand and reducing the carbon footprints of the dairy sector on the other. The development of genomics techniques has enabled genome wide variant calling, to detect SNPs associated with the desired phenotypes. In this study, we used a comparative genomics approach to detect genetic variation associated with thermotolerance and to design molecular markers for characterizing the animals as tolerant/sensitive. A total of 40 cows from each group were split in four sequencing pools and a whole‐genome sequencing approach was used. Results and conclusion: Genome‐wide genetic variation between groups was characterized and enrichment analysis revealed specific pathways which participate in the adaptive mechanisms of thermotolerance, implicated into systemic and cellular responses, including the immune system functionality, Heat Stress and Unfolded Protein Response. The markers made a promising set of results, as specific SNPs in five genes encoding for Heat Shock Proteins were significantly associated with thermotolerance.

Heat Stress: A Serious Disruptor of the Reproductive Physiology of Dairy Cows

“…These specific pathways revealed specific parts of the genetic basis of the phenotypical characteristics, and allowed for the annotation of specific SNPs (e.g., rs135169588, rs41255191, rs41964478, and rs136591078) mapped in five genes encoding HSPs (DNAJC27, DNAJA4, DNAJC21, DNAJB1, and HSPA1A). These SNPs could be used for genetic selection for thermotolerance [38].…”

“…The vision of creating a new cattle population with inherent increased thermal resilience, requiring only moderate artificial cooling, is not unrealistic. This population could be developed through intense selection for thermotolerance [38,207] and productivity using the available modern omics technologies (genomics, transcriptomics, proteomics, metabolomics, etc.). Carefully selected individuals could be subsequently bred through planned breeding programs, predominantly using embryo transfer technologies.…”