We’ve known for a long time that the digestive system (horse and human) is home to an abundance of microbes, including bacteria. However it now seems that the complex ‘community’ living in the horses’ gut could provide valuable information about ageing and obesity…

Why are gut microbes so important?

Your horse’s large intestine or ‘hind gut’ is home to a trillions of tiny living cells (microbes) including bacteria, viruses and fungi which are essential for fibre digestion and helping to regulate the immune system. In people, differences in the ‘community’ of gut microbes (the microbiota) and their genetic make-up (the microbiome) have been linked to various aspects of health and disease, raising the question of whether the same might be true for horses.

Horse eating grass

Obesity, age & gut microbes

In terms of gut microbes, ‘diversity’ is a measure of the number of different species, the abundance of species and the distribution or ‘evenness’ of species within the community. In people, a reduction in diversity has been linked to both ageing and obesity. A similar reduction in diversity has also been seen in elderly horses (as opposed to ponies), regardless of diet.

New findings…

In a newly published study, faecal samples from obese ponies, aged ponies and healthy controls (ponies that were neither obese nor aged) fed the same diet were analysed to assess differences in their gut microbes. Surprisingly, diversity significantly increased in obese ponies which is the opposite of what has been seen in obese people, and tended to increase in aged ponies; the opposite of what has been seen in aged horses and people. However, it was not possible to consistently predict whether ponies belonged to the aged, obese or control group by looking at differences in faecel microbes alone.

What does this mean & why does it matter?

It seems that for ponies, obesity has a greater effect on gut microbes than age. The fact that microbial diversity has been seen to decrease in aged horses but not ponies could suggest that physiologically speaking, ponies ‘age later’ than horses as they tend to live longer. It’s not yet clear why it wasn’t possible consistently predict whether ponies were aged or obese by looking at faecal microbes, but it could be because microbes in the droppings only tell us what is happening in part of the digestive system. Another possible explanation is that some species of microbes are capable of performing more than one ‘job’. This could mean that there may be several different profiles of species associated with ageing or obesity in ponies.  When it comes to understanding the link between gut microbes, age and obesity we have only just scratched the surface. However more work in this area could ultimately lead to improvements in the way we feed older and/ or obese horse and ponies.

Did you know?

This new research entitled ‘The equine gastrointestinal microbiome: Impacts of age and obesity.’ was carried out in collaboration with SPILLERS as part of our on-going work to improve our understanding of ageing and obesity.  We hope that by investing and taking part in research, we can help to improve the health & welfare of horses and ponies throughout the world.

For advice on managing overweight horses & ponies contact the SPILLERS Care-Line


Morrison PK , Newbold CJ ,   Jones E ,   Worgan HJ,  Grove-White DH,  H. Dugdale AH ,  Barfoot C, Harris PA  & Argo CM (2018) The equine gastrointestinal microbiome: Impacts of age and obesity. Front. Microbiol., 07 December 2018 https://doi.org/10.3389/fmicb.2018.03017