Genome-wide DNA methylation in cows subjected to different stress level as assessed by cortisol in milk

To assess how different levels of stress exposure affect epigenetic regulation mechanisms in cattle, we investigated genome-wide DNA methylation in 20 Italian Red Pied dairy cows falling in the high- and low-variant tails of the distribution of milk cortisol concentration (MC), a neuroendocrine biomarker of stress in dairy cows, measured in 126 animals belonging to the same farm in the framework of the Gen2Phen Italian project. The 'low-' and 'high-cortisol' groups of animals had MC<370 pg/ml and>810 pg/ml, respectively. Their methylome was analysed by Reduced Representation Bisulfite Sequencing, which provides single-base resolution methylation profiles across the whole genome. To date, 20 animals (10 low- and 10 high-MC) have been sequenced. The two groups showed similar proportion of methylation at CpG sites, while they differed at non-CpG sites. Significant methylation changes were observed in 897 regions and 248 genes. KEGG and Gene Ontology (GO) pathway analyses indicated that these genes were mainly involved in immune regulatory pathways, glucocorticoids metabolism and nervous system functions. These preliminary results suggest that cortisol secretion in livestock is mediated by epigenetic regulation, provide target biomarkers to assess the effect of stress management procedures and candidate genes for the selection of stress-tolerant animals. Overall design: Cows were ranked on the basis of cortisol in the milk and the 10 cows with the higher and the 10 cows with the lower concentrations were selected for epigenome analysis