It is well known that women live longer than men on average and new research from New Zealand has now highlighted the reasons - and what men might have to lose to reset their biological clocks.

In a study published today in the scientific journal eLife, researchers from the University of Otago have teamed up with scientists in the US to probe the effects that male hormones have on DNA and have singled out a famous New Zealand animal as an example.

Studying sheep, the researchers found that removing male hormones delays the ageing of DNA.

If that sounds painful, it should.

"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," says University of Otago Anatomy PhD student Victoria Sugrue, first-author of the study,

Researchers also found that castration "drives feminine characteristics of DNA".

To obtain their results the researchers needed to generate an "epigenetic clock", a biochemical test based on DNA methylation, to measure ageing in a large group of sheep.

DNA methylation is an epigenetic mechanism that modifies the function of genes.

When researchers examined the epigenetic clocks of castrated and intact male sheep, they found differing "ticking rates"; meaning they could see that the longer lifespans of castrated males (or wethers) were written in their DNA.

Dr Tim Hore, research team co-leader and senior lecturer at Otago's Department of Anatomy, says the findings provide new ways to understand how male-accelerated ageing works.

"We found that males and females have very different patterns of DNA ageing in sheep; and that 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," Hore says.

Researchers also hope that their work could help farmers determine which sheep will live longest or be most productive and could also assist with identifying mutton that has been dressed (and marketed) as tender New Zealand lamb.

Shrek, our nutless wonder

2004 was a simpler time. We stood united as a nation in awe of a humble sheep.

Shrek was a Merino that escaped muster for years, developing a fearsome fleece.

He roamed the wilds of Central Otago before he was eventually shorn on television, giving up a whopping 27kg of wool.

Shrek the Sheep was a New Zealand legend - and he did it all without his testicles. (Photo / Supplied)

Stardom followed, as Shrek made numerous appearances, met then Prime Minister Helen Clark and was later shorn again on an iceberg.

And the legend did it all without the family jewels.

He eventually made it to the grand old age of 16.

"By the time Shrek was caught he was already 10 years old - roughly the maximum age of the most long-lived sheep on a commercial farm. I think at least part of Shrek's fame was simply that he lived so long - which almost certainly wouldn't have happened if he was not castrated," Hore says.