Dr Shannon Clarke says the epigenetic clock can help identify stock whose genetic composition is actually younger than the animal’s age.
An AgResearch team is using methylomes for aging that may help with identifying animals’ productive rates. The scientists have developed a livestock clock that can accurately predict an animal’s age within the four key livestock species. Richard Rennie reports.
Having a biological age and a chronological age can mean two differing numbers, as many online fitness assessment tests will often disappointingly testify. But AgResearch scientists are using that difference to help identify animals that may prove to be productive well beyond what their chronological age suggests.
The rapidly developing area of methylomics has scientists studying the natural modifications of DNA that happens to living organisms during their development and aging, and changes that happen to the genome when that organism experiences a sustained, stressful event.
It is the science that has them looking two to three generations beyond the occurrence to see if it has been passed on, possibly providing a better strain of forages or livestock capable of greater resilience or productivity in the face of similar stress events in their lifetime, such as drought.
“But our latest work has us working on an epigenetic clock, which uses DNA methylation to make an accurate prediction of chronological age,” AgResearch lead researcher Dr Shannon Clarke said.
The scientists have developed a livestock clock that can accurately predict an animal’s age within the four key livestock species of goat, deer, sheep and cattle, with a very high .97 correlation coefficient.
A similar human clock, the Horvath Clock, can estimate human age with the same accuracy and a median error of 3.6 years.
In itself this has a practical application for farmers in areas where birth date is not known for livestock, such as cattle in the Australian outback, or for conservationists trying to age wildlife.
“But the next step is to look at the deviation between the epigenetic age and the chronological age and if there is, whether it has been caused by stress and external factors, such as drought or disease,” she said.
“From there, we would want to see if we could utilise this methylome profile to make selection decisions based on that accelerated or slowed biological aging.”
So far researchers have established a baseline epigenetic clock across all species, and only with time and increased sampling will they see how much those individual species vary from that “all species” base.
Some work on human studies suggests these methylation affected genetics may be able to be passed on.
Victims of the Dutch famine from 1944-1945, where 20,000 people died, also included pregnant women whose children showed signs of inherited response to the stress their mothers experienced.
This included them ending up several kilograms heavier than average, having higher cholesterol in middle age, high obesity rates and diabetes. Overall, they experienced a 10% higher mortality rate than cohorts born either side of them.
Scientists believe the process of methylomics silenced critical genes in the unborn children when their mothers were stressed and they stayed silent after birth.
“For our work we would need three generations of animals to see if those traits are passed on,” she said.
“It is also very difficult from an ethical point of view to stress animals. We are compelled to use animals stressed by naturally occurring events, particularly facial eczema.
“What we would like to progress to is whether we can find from methylation an indicator we can add into a breeding performance index, one that highlights how they may be better at performing under a particular stressor or condition.”
Conversely, researchers may be able to also highlight how a particular line of stock, while being a certain chronological age are actually likely to underperform because they are epigenetically older and possibly unlikely to reach full potential
They are still to determine whether the methylomic effect is likely to be greater in females than males.
“And we have not determined at what stage a stressful event could bring a genetic change, whether it is before mating after, before birth or at weaning,” she said.
“This would affect when we actually determine that biological age. The first step for us really is just to determine that epigenetic clock as a baseline to measure stress.”
