Development of epigenetic clocks for New Zealand livestock
Robust biological biomarkers of chronological age have been developed in humans and model mammalian species such as rats and mice using DNA methylation data. The concept of these so-called "epigenetic clocks" has emerged from a large body of literature describing the correlation between genome-wide methylation levels and age. Epigenetic clocks exploit this phenomenon and use small panels of differentially methylated cytosine (CpG) sites to make robust predictions of chronological age, independent of tissue type. Here we present highly accurate livestock epigenetic clocks whereby we have used the custom mammalian methylation array "HorvathMammalMethyl40"1 to construct the first epigenetic clock for domesticated goat (Capra hircus), cattle (Bos taurus), Red (Cervus elaphus) and Wapiti deer (Cervus canadensis) and composite-breed sheep (Ovis aries). Additionally, we have constructed a New Zealand livestock farm animal clock for all animals included in the study, which will enable robust predictions to be extended to various breeds. The farm animal clock shows similarly high accuracies to the individual species clocks (r>0.97), utilising only 217 CpG sites to estimate age (relative to the maximum lifespan of the species) with a single mathematical model. We envision that the applications of this livestock clock could extend well beyond the scope of chronological age estimates. Many independent studies have demonstrated that a deviation between true age and clock derived molecular age is indicative of past and/or present health (including stress) status. There is, therefore, untapped potential to utilise livestock clocks in breeding programmes as a predictor for age-related, production traits.