Changes in DNA Methylation in Cow Blood Associated With Age and Disease

DNA methylation is among the most promising biomarkers for age prediction, enabling the development of epigenetic clocks that correlate methylation profiles with chronological age. In this study, we investigated the relationship between ageing and disease susceptibility, focusing on both nuclear and mitochondrial DNA methylation in dairy cows. Genome-wide DNA methylation profiling was performed using enzymatic methyl-seq, covering 53 million CpG sites. The dataset included 96 cows with different phenotypes, sampled cross-sectionally and ranging from 2 to 9 years of age. We applied elastic net regression to identify the most predictive CpG sites for age estimation, achieving a mean absolute error of 111 days with a strong correlation to chronological age r = 0.97. Beyond chronological age prediction, we assessed the impact of disease status on epigenetic ageing. Our results revealed accelerated epigenetic ageing in cows susceptible to diseases, suggesting a link between health-related stress and disrupted DNA methylation dynamics. We further identified age-associated promoter methylation changes, particularly in MAB21L1, which may play a role in molecular ageing mechanisms. Additionally, we observed a decline in mitochondrial DNA methylation with age, notably in genes encoding Cytochrome c oxidase (COX), indicating a possible connection between mitochondrial dysfunction and epigenetic regulation. An inverse correlation between D-loop methylation and mtDNA copy number was also observed. This study demonstrates the potential of epigenetic models for biological age prediction in livestock, while recognizing that their accuracy may vary among species with different lifespans. Overall design: Blood samples were collected from cows at a Vancouver farm between November 2020 and February 2021. Two years later, we selected 48 cows that had been culled due to complications related to infertility (BFR, n=6), mastitis (BMS, n=6), lameness (BFL, n=12), metabolic disorders (BMT, n=6), or low production (n=18), which were not identified at the time of sampling. This culling reason was recorded in farm management logs and represented the primary cause for culling. These cows formed the “diseased group.” For comparison, we selected a second group of 48 cows that remained in the herd without any health issues. This second group represented the “control group.” The ages of the cows in both groups ranged from 1.8 to 9.2 years. *************************************************************** The table below lists GEO accessions reused/reanalyzed for this study. ***************************************************************