We know our dogs change as they get older. But new research suggests something else may be ageing alongside them – the trillions of microorganisms living in their gut.
A major study from the Dog Aging Project, published in Nature Communications in 2026, analysed the gut microbiomes of 922 pet dogs, ranging from just 8 months to 18 years old.
The researchers found something fascinating: the canine gut microbiome changes with age, and microbial diversity tends to decline as dogs get older.
So, what could this mean for the way we think about healthy ageing in our dogs?
The gut microbiome changes with age
Researchers analysed faecal samples using shotgun metagenomic sequencing, allowing them to look in detail at the microorganisms and microbial functions present within each dog's gut.
One of the clearest findings was that microbial diversity decreased significantly with age. This relationship remained even when researchers accounted for factors including health status, sex, weight and breed size. Older dogs also had differences in the overall composition of their microbiomes compared with younger dogs.
The researchers identified age-related changes involving:
- 147 bacterial species
- 46 bacterial genera
- 7 bacterial phyla
Some bacteria became more abundant with age, while others decreased.
Rather than one particular bacterium changing as dogs grow older, the research suggests that the whole gut ecosystem gradually shifts throughout a dog's life.
Why does microbial diversity matter?
The gut microbiome is an ecosystem containing many different microorganisms performing different functions. These microbes interact with food, produce metabolites, communicate with the immune system and compete with other microorganisms for nutrients and space.
That's why at Biome4Pets we don't assess bacteria in isolation. We look at the wider microbial community, including its diversity and overall balance.
The finding that diversity tends to decrease with age raises an interesting question:
Could maintaining a diverse and resilient microbiome become increasingly important as our dogs get older?
This study doesn't answer that yet, but it certainly gives researchers a reason to investigate further.
Could scientists tell a dog's age from its microbiome?
One of the most intriguing parts of the study was that researchers found enough of an age-related microbial pattern to build a model that attempted to predict a dog's age from its microbiome.
It wasn't precise enough to replace knowing your dog's birthday - the average error was around 2.6 years. But that's not really the interesting part.
The fact that an identifiable age signature exists within the microbiome at all suggests that the microbial ecosystem reflects some of the biological changes taking place as a dog moves through life.
Age wasn't the only factor - diet mattered too
Researchers also found significant associations between diet and microbiome composition. Dogs eating different types of food, including commercial dry food, raw diets and home-cooked diets, showed differences in their microbial communities.
This is important because it reminds us that ageing doesn't affect the microbiome in isolation. A dog's gut ecosystem is shaped throughout life by diet, health, environment, medication and lifestyle.
Two dogs can therefore be exactly the same age but have very different microbiomes.
What does this mean for an older dog?
The research doesn't show that microbiome changes cause ageing, nor does it suggest that changing the microbiome can make an older dog younger.
What it does show is that the microbiome is dynamic and continues to change throughout life.
That could become particularly relevant when an older dog starts experiencing:
- less consistent stools
- increased digestive sensitivity
- difficulty tolerating foods they previously ate
- changes following medication or antibiotics
- recurrent gastrointestinal problems
Rather than simply assuming every digestive change is an inevitable consequence of getting older, it may be useful to understand what is happening within that individual dog's gut.
Healthy ageing is about more than the number of birthdays
We spend a lot of time thinking about helping our dogs live longer. Perhaps the more important question is how we help them remain healthier for longer. Nutrition, exercise, maintaining a healthy weight and good veterinary care are all important. Increasingly, the microbiome may become another part of that picture.
This Dog Aging Project study provides compelling evidence that the microbial ecosystem inside our dogs changes as they move through life. And understanding those changes could eventually help us better understand healthy canine ageing itself.
Your dog's birthday tells you how many years they've lived. Their microbiome may tell us something about what's been happening inside them along the way.
Concerned about your older dog's gut health?
If your dog has developed digestive changes, food sensitivities or other gut-related problems as they've become older, microbiome testing can provide a detailed picture of the bacterial community currently living in their gut.
Rather than guessing, we can look at microbial diversity, identify imbalances and interpret the findings alongside your dog's age, diet and health history.
Find out what your dog's microbiome can tell you.
