How your dog’s gut health affects their immune system

Most owners know gut health for dogs matters, but did you know its effects reach far beyond the digestive system? A large part of the immune system sits in the gut, and ongoing research is allowing us to see the impact this has on other areas of the body.
 
So, if you have a pet with recurrent skin flare-ups, low energy, or frequent minor illnesses, perhaps their gut health has something to do with it…
 
In this guide, we will explore how a healthy gut and immune system normally function, signs that your dog’s gut might need a little support, and ways to help your pet with this. Read on to find out more!

What is the gut immune connection?

When most people think about the gut, they think about digestion. While processing food is a key role, the digestive system is a bit more complicated than that. The gut is actually a carefully balanced ecosystem, and it plays an important part in the overall health of us and our pets.
 
Within the gut, you will find millions of helpful bacteria, fungi, and viruses which are not only responsible for helping break down food to access nutrients, but they also support your dog’s immune defences.

These organisms are known collectively as the gut microbiome.

Gut immune cells

When you think about it, the gut is constantly exposed to a high level of stimulation. This includes contamination from the environment, potential allergens found in the diet, and other microbes. So, it’s important that these immune cells are primed and ready to stop any would-be attackers.  At the same time, they also mustn’t overreact to non-harmful elements, like dietary proteins.
 
These highly specialised cells are found in the gut-associated lymphoid tissue (GALT), where their job is to identify potential threats and initiate an appropriate immune response.
 
The microbiome has a big role in shaping the way that GALT operates. Healthy gut bacteria are responsible for ‘training’ immune cells and the way they respond. In animals with alterations to their gut microbiome, we can see problems arising like chronic inflammation or hypersensitivity (allergy) reactions.

Physical barrier

As well as the immune cells, the gut lining itself also acts as a physical barrier to harmful pathogens (namely invading bacteria and pathogens). A healthy gut microbiome has a positive effect on the gut lining, helping it to maintain tight gaps between its cells, produce the right amount of mucus, and allow efficient nutrient absorption.
 
When the gut lining is compromised due to alterations in healthy microorganism levels (dysbiosis), we can see larger gaps between cells, leading to ‘leaky gut syndrome’. This allows pathogens to leave the intestines that would otherwise normally pass through our pet’s digestive system. Here they can get into your dog’s blood circulation, resulting in increased disease and chronic inflammation risks elsewhere in the body.  
 
‘Leaky gut syndrome’ most commonly occurs due to long-term intestinal damage or microbiome imbalance but may also be seen secondary to toxin ingestion or trauma.
 
By having the right level of ‘friendly bacteria’ in the gut, we can help to keep a variety of body systems in balance.

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What happens when the gut breaks down?

When things are not functioning as well as they should be, we can see many possible signs of poor gut health in dogs. Some of these are localised to the gut itself, such as vomiting, diarrhoea, excess gas, and abdominal discomfort. Others may be more wide-ranging, such as chronic skin complaints, including allergy flares and recurrent infections. We may also see alterations in mood and perhaps even an increase in joint pain.
 
That is because of the influence of gut health on other areas of the body, due to alterations to your dog’s immune system and chemical signals.
 
We’ll explore this in a little more detail next.

How gut health affects other areas of the body

There is a lot of research going on into the ways that gut health can affect our dogs. The exact impact can vary from dog to dog, but these are the current areas of interest.

Skin and Coat

There is a pathway of communication that exists between the skin and the gut, known as the gut-skin axis. This connection means that the health of one can affect the health and function of the other.
 
When your dog’s gut microbiome is compromised, this can have an impact on the skin, affecting immunological health and inflammatory conditions, like skin allergies. Also, dogs with an imbalance in their gut microbiome may not be absorbing nutrients from the diet as effectively, which can in turn affect skin and coat condition. Symptoms may include a dull coat, flaky skin, and increased itchiness.
 
A recent study showed that dogs with atopic dermatitis (skin allergies) have lowered gut microbial diversity compared to healthy dogs. It was also shown that probiotic administration can reduce the clinical severity of their skin allergy symptoms. While research is ongoing in this area, it’s certainly an interesting development.

Mood and Behaviour

The gut-brain axis describes the communication channel that exists between the gut and the brain. We know that the brain can influence gut function (think stress-induced colitis!), but the gut can also communicate to the brain, affecting things like behaviour and mood.
 
In people, a variety of studies exist suggesting that bacteria and their byproducts can activate nerve fibres and possibly affect immune, hormonal, and neurochemical systems in the body, which can have an impact on the brain.
 
We also know that the gut is responsible for producing around 90 -95% of your dog’s serotonin, a powerful hormone that regulates mood and cognitive function. Low serotonin levels are linked with issues like anxiety, stress, and depression.
 
A recent 2025 review paper looking at dogs specifically states in their findings, ‘This indicates there are potentially meaningful relationships identified between the gut microbiome composition and aggressive behaviour and fearfulness/ fearful behaviours, which warrant further investigation.’
 
So, while studies are ongoing, there is a clear emerging link between alterations in gut microbiome and your dog’s mood.

Joints and Mobility

This is another area that is currently undergoing investigation. It’s thought that chronic, low-grade gut inflammation can have an impact on joint pain and mobility, especially in senior and arthritic dogs.
 
When exploring the variation in gut microbes between healthy and arthritic dogs, one study in 2020 stated the following: ‘the results obtained suggested that it might influence the degeneration of joints and bones through the propagation of systemic inflammation’.
 
This is an interesting area of research. Pet owners should remember to speak to their vet about suspected joint pain in dogs, as there are various underlying causes for this and many pets will benefit from proper management and pain relief.  

Digestion

When your dog’s gut health is reduced, we often see symptoms such as diarrhoea, vomiting, increased gas, or an increased volume of mucus in your pet’s stools. As we discussed earlier, the microbiome is essential for your pet’s digestion, and an alteration in the levels of helpful microorganisms can have many detrimental effects. Dysbiosis disrupts GALT activation, which can cause chronic inflammation or hypersensitivity (allergy) reactions. Common reasons why the normal gut microbiome may be disrupted include –

• Medication e.g. antibiotics
• Sudden changes in diet
• Stress
• Ageing    
  

Don’t forget it’s important to rule out other underlying health issues with your vet first, as many conditions can cause similar digestive symptoms.

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Signs your dog's gut and immune system may need support

Signs of poor gut health in dogs may include -
 
Digestive signs -

• Loose stools (which may range from softer than normal, through to liquid diarrhoea)
• Vomiting
• Increased mucus in faeces
• Bloody stools
• Increased gas
• Abdominal discomfort
  

Other signs –

• Itchy or dull coat
• Reduced energy levels
• Bad breath
• Recurrent minor illnesses or infections
• Low mood

How to Support Your Dog’s Gut Health and Immune System

Nutritionally complete diet

A good-quality, nutritionally complete diet is essential for a well functioning immune system and good gut health in dogs. Choose a diet that is appropriate for your dog’s age, size, and life stage to ensure they are getting everything they need. Your vet will chat you through hypoallergenic diets if dietary allergies are suspected. Don’t forget that commercial brands will give you instructions on the correct amounts to feed your pet, which you should follow. Homecooked diets must be formulated with the help of a veterinary nutritionist, as it can be easy to accidentally cause nutritional imbalances.
 
If you decide to make a change to your pet’s diet, be sure to do this gradually. Any new foods should be introduced slowly over 7 – 10 days to help their gut microbiome adapt. Too fast, and you may accidentally trigger more tummy troubles! Plus don’t forget to skip table scraps and leftovers, for some pet’s these can set off stomach upsets too.

Manage routine and stress

Maintain a consistent routine so that your pet knows what to expect each day. This will help reduce problems like anxiety and long-term stress, which we know can have an impact on gut health in dogs. Regular feeding times will also help with your pet’s digestion. Keeping their environment calm and safe will also help to reduce behavioural issues.

Regular exercise

Regular exercise will keep your pet fit and their digestion regular. Exercise is also a great mood booster and helps reduce the likelihood of behavioural issues developing. Why not try mixing up your walks a bit or playing a few new games with your pet to give them some variety?

Use probiotics (and prebiotics)

For some dogs, prebiotics and probiotics can help to get things back on track. Probiotics are live bacteria that help to balance your pet’s microbiome; prebiotics are fibres that help to feed these beneficial microorganisms, helping them to multiply.
 
Supplements can be used as a long-term measure, especially for those pets with chronic or recurrent health issues, or they can be used short-term if your dog has a one-off stomach upset. While probiotics are beneficial to many pets, it’s always a good idea to speak to your vet for advice before starting.

Speak to your vet

Regular vet checks are an essential part of keeping your dog’s immune system healthy, through preventative treatments like vaccinations and parasite control. These check-ups also help to identify emerging problems sooner, such as weight loss, coat changes, or dental disease.  
 
We always recommend speaking to your vet before your next routine appointment if something’s not right with your dog. It’s important to rule out other health issues, just in case there is an underlying metabolic or parasitic cause for their symptoms. Your vet will chat through signs of poor gut health in dogs and examine your pet before deciding on an appropriate plan.
 
Prompt intervention often leads to better outcomes, so don’t put off seeking help for your pet.

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Conclusion

Our understanding of the impact of good gut health for dogs is constantly evolving. But one thing’s for sure, the microbiome for maintaining healthy digestion and immune function.
 
If you think your dog is struggling with their gut health, or you’re wondering whether another body system is becoming affected, speak to your vet for advice. They will help to rule out other potential issues and be able to recommend a plan for your pet. If nothing seems amiss, then the right diet, probiotics, and a change in lifestyle may all help get your pet back on track again.