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DNA methylation has proven to be the most promising age-predictive biomarker in mammals resulting in the emergence of ‘epigenetic clocks’ that describe the relationship between methylation levels and age. Using Targeted bisulfite Sequencing, we evaluated blood DNA-methylation data from 96 domesticated cows (Bos Taurus) of which 88 were adults and 8 were calves. This allowed us to measure DNA methylation across three thousand regions in the genome that were conserved across mammals. The significant association of age with the changes in DNA methylation enabled us to construct an epigenetic clock that predicts the age of cows to within nine months. We also investigated whether factors exist that moderate the association between epigenetic age and actual age and found that milk production levels significantly increase the rate of epigenetic ageing, suggesting that the stress of excessive milk production might be accelerating epigenetic ageing in cows.

Unlike genomes, which are static throughout the lifespan of an organism, DNA methylomes are dynamic. To study these dynamics, we developed quantitative models that measure the effect of multiple factors on DNA methylomes including, age, sex, weight, and genetics. We conducted our study in canids, which prove to be an ideal species to assess epigenetic moderators due to their extreme variability in size and well-characterized genetic structure. We collected buccal swabs from 217 canids (207 domestic dogs and 10 grey wolves) and used targeted bisulphite sequencing to measure methylomes. We also measured genotypes at over one thousand single nucleotide polymorphisms (SNPs). As expected, we found that DNA methylomes are strongly associated with age, enabling the construction of epigenetic clocks. However, we also identify novel associations between methylomes and sex, weight, and sterilization status, leading to accurate models that predict these factors. Methylomes are also affected by genetics, and we observe multiple associations between SNP loci and methylated CpGs. Finally, we show that several factors moderate the relationship between epigenetic ages and real ages, such as body weight, which increases epigenetic ageing. In conclusion, we demonstrate that the plasticity of DNA methylomes is impacted by myriad genetics and physiological factors, and that DNA methylation biomarkers are accurate predictors of age, sex and sterilization status.