The study, led by researchers from the University of Otago in New Zealand, showed that removal of androgen hormone in sheep delays ageing of DNA, and that it also drives feminine characteristics of DNA and the chemical tags it holds, known as DNA methylation. 

Androgens are a group of hormones that play a role in male traits and reproductive activity. It is usually thought of as male hormone, but the female body also produces a small amount of androgens naturally. 

"Both farmers and scientists have known for some time that removing male hormones by castration improves longevity compared to their intact counterparts; however, this is the first time anyone has looked at DNA to see if it also ages slower," said first-author Victoria Sugrue, doctoral student at the varsity. 

For the study, published in the journal eLife, the team first generated an 'epigenetic clock' from large numbers of sheep to measure DNA ageing. They then looked at the epigenetic clock of castrated and intact males and found their 'ticking rate' is different; meaning that the longer lives of castrated sheep, or 'wethers' as they are referred to by farmers, is reflected in their DNA. 

The findings provide new avenues to understand the mechanism of male-accelerated ageing. The team found that males and females have very different patterns of DNA ageing in sheep. Despite being male, the castrates (wethers) had very feminine characteristics at specific DNA sites. 

"Interestingly, those sites most affected by castration also bind to receptors of male hormones in humans at a much greater rate than we would expect by chance. This provides a clear link between castration, male hormones and sex-specific differences in DNA ageing," said Tim Hore, senior lecturer at Otago's Department of Anatomy.