📌 Key Takeaways
- ✅ 70% to 80% of a dog's immune system is located in the gut wall, so gut health affects the whole body
- ✅ Stools that swing between soft and firm, and unusually smelly farts, are signs of an unstable microbiome
- ✅ When choosing a probiotic, look at CFU, multi-strain formulas, and third-party verification
- ✅ Don't feed the same product long-term; rotate brands and strains
- ✅ For diarrhoea, fast for 24 hours first and provide water; if it lasts more than two days with vomiting, see a veterinarian
Has your dog been having loose stools, unusually smelly farts, or even becoming easily startled and anxious for no reason? Many owners blame the dog food first, but the real answer may lie in the 'invisible organ' inside your dog's gut—the gut microbiome. Research shows that 70% to 80% of a dog's immune system is located in the gut wall, and gut bacteria influence mood and behaviour through the 'gut-brain axis'. Below we break down 5 gut warning signs, 3 criteria for choosing a probiotic, and 4 daily habits to support gut health.
The gut is a dog's 'second brain'
The gut does more than digest food. The bacterial community in the gut helps dogs break down food, absorb nutrients, maintain the body's detoxification pathways, and produce vitamin B12, vitamin K, and various neurotransmitters including serotonin, dopamine, and GABA—substances directly linked to emotional stability and sleep quality.
More importantly, there is a two-way 'highway' between the gut and the brain. The vagus nerve runs from the brainstem to the abdomen, connecting the central nervous system with the enteric nervous system. Beneficial bacteria help keep the body in balance by 'turning off the tap' on cortisol and adrenaline; conversely, chronic stress keeps these two hormones persistently high, causing damage to the body.
A 2019 study from Oregon State University in the US: researchers collected gut bacteria samples from 31 dogs rescued from dogfighting organisations and divided them into two groups based on aggressive behaviour. They found that aggressive dogs had significantly higher levels of certain bacteria in their guts. This supports an important idea—anxiety can sometimes be linked to aggressive behaviour, and the root of anxiety can be traced back to the gut and its microbes.
What disrupts a dog's gut microbiome?
Environmental chemicals, fertilisers, contaminated water, artificial sugars, antibiotics, and non-steroidal anti-inflammatory drugs (NSAIDs) can all kill or alter bacterial communities. Emotional stress, trauma (including surgery), gastrointestinal illness, nutritional deficiencies, or long-term feeding of highly processed foods can also cause damage.
5 warning signs of an imbalanced gut microbiome
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Inconsistent stools: sometimes soft, sometimes watery, sometimes firm—this means the microbiome is unstable.
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Unusually smelly farts and bloating: incompletely digested food ferments in the gut.
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Variable appetite: sometimes eating the same food quickly, sometimes sniffing and walking away.
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Easily stressed: easily frightened, barking a lot, overreacting to surroundings, or even showing aggressive behaviour.
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Dull coat and premature greying: the book notes that premature greying and behavioural deterioration are signs of excessive stress.
How to choose a dog probiotic: 3 key criteria
There are many canine probiotic formulas on the market. Look at three things when choosing:
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High enough CFU: CFU (colony-forming units) represents the number of live bacteria; the higher the number, the more live bacteria theoretically reach the gut.
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Multi-strain blend: different strains such as Lactobacillus and Bifidobacterium have different properties. Research shows that specific probiotics can reduce anxiety- and depression-related behaviours.
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Third-party verification: independent verification of a product's viability and efficacy is more credible than the brand's own claims.
An often-overlooked point: rotation
It's not advisable to use the same dog probiotic long-term. The book recommends 'rotating different brands and types'—different strains and spores have different properties, and rotation helps diversify the dog's gut microbiome. In addition, probiotic and digestive enzyme blends can also be very helpful for many dogs.
4 ways to build a healthy gut microbiome (prebiotics + postbiotics)
Probiotic supplements alone aren't enough; you also need to feed the good bacteria.
Tip 1: Diversify the diet and add prebiotics
Dietary fibre and polyphenols are 'fuel' for good bacteria. Note that polyphenols are sensitive to heat, and ultra-processed pet foods destroy polyphenols during manufacturing, so 'eating fresh' is especially important for gut health.
Tip 2: Prebiotics + probiotics = postbiotics
Prebiotic foods combined with probiotics (fermented foods or supplements) produce 'postbiotics'. Fermented vegetables and unsweetened kefir are excellent probiotic food sources, but many dogs won't accept their pungent smell; if your dog will eat them, they can be a probiotic source—if not, use a rotating brand of supplement instead.
Tip 3: Daily exercise + free sniffing
Research shows that just two minutes of exercise every hour can reduce the risk of death from any cause. Exercise reduces restlessness and improves sleep, and letting dogs sniff, dig, and play on grass that hasn't been sprayed with chemicals also has a positive effect on the microbiome. What urban dogs lack most is exactly these opportunities to 'put four paws on the soil'.
Tip 4: Reduce disruptive factors
Antibiotics, artificial sugars, NSAIDs, environmental chemicals, and chronic stress can all 'wipe out' good bacteria. Antibiotics must be prescribed by a veterinarian; during and after treatment, discuss with your veterinarian how to support the gut microbiome.
How to feed a dog during diarrhoea: 3 steps
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Fast for 24 hours first, and keep clean drinking water available at all times. If there is also vomiting, offer only small amounts of water.
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After 24 hours, feed bland food: boiled chicken, boiled fish, rice, etc., 3 to 4 times a day, in small portions, until stools return to normal.
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Gradually reintroduce food: once stools are normal, take several days to slowly return to the normal feeding routine. Never change suddenly, or you may trigger another round of diarrhoea.
⚠️ If diarrhoea lasts more than two days and is accompanied by vomiting, seek veterinary care as soon as possible.
PetChill's Reminder
The gut is a dog's 'second brain', and its health shows in stools, mood, and coat. Rather than waiting for diarrhoea to take action, start today: feed a varied diet, provide daily exercise and sniffing, and rotate probiotic brands when needed. Remember, any dietary change should be gradual—your dog's gut needs time to adapt.
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