Why Does My Dog’s Poo Smell So Bad? The Dietary Cause and Fix

Part of our Complete Guide to Dog Digestive Health.

Every dog's poo has a smell. But if you find yourself actively dreading your dog's toilet trips, keeping air freshener permanently stocked or apologising to guests, that is not normal — and it is almost certainly being caused by what your dog is eating.

The good news: smelly dog poo is one of the most fixable digestive problems in dogs. Once you understand the cause, the solution is straightforward.

Why Does Dog Poo Smell So Bad?

The smell of dog faeces is determined by what happens in the large intestine. When a dog's digestive system is working efficiently, protein is fully absorbed in the small intestine and very little reaches the large intestine. When protein is not fully absorbed — due to poor digestibility or a gut that struggles to process it — that undigested protein travels to the large intestine where gut bacteria ferment it.

This fermentation produces a range of compounds including:

• Ammonia — sharp, pungent odour
• Phenols and indoles — the compounds most directly responsible for that deep, faecal smell
• Hydrogen sulphide — the classic rotten egg odour
• Amines — fish-like or rancid smells

The more undigested protein that reaches the large intestine, the more fermentation occurs, and the worse the smell. This is why protein digestibility is the most direct lever for controlling faecal odour in dogs.

What Makes Dog Poo Smell Worse Than It Should?

• Low protein digestibility in the food — the biggest factor. A food with 80% protein digestibility leaves 20% of the protein unabsorbed to ferment.
• Food intolerances — a protein the gut cannot process efficiently causes more fermentation than normal
• High meat content without adequate digestibility — more protein going in means more protein potentially fermenting
• Artificial additives and low-quality ingredients — these can disrupt the gut microbiome and worsen fermentation
• Disrupted gut microbiome — an imbalance of gut bacteria changes what compounds are produced during fermentation

The Science: What the Research Shows

A published study (Lin et al., 2019, Journal of Animal Science) measured the effect of TruPet™ postbiotic supplementation in dogs. One of the key findings: dogs supplemented with TruPet™ showed significantly reduced faecal phenol and total faecal phenol + indole concentrations — the primary odour-causing compounds in dog faeces.

Combined with a protein digestibility of 95% — meaning far less undigested protein reaching the large intestine to ferment in the first place — the effect on faecal odour in dogs fed our Hydrolysed Digestive Care Dog Food is twofold: less fermentation substrate and a gut microbiome better equipped to manage what remains.

How to Fix Smelly Dog Poo Through Diet

Step 1: Switch to a Higher Digestibility Food

The single most impactful change you can make. A food with 95% protein digestibility produces dramatically less fermentation — and dramatically less odour — than one at 80%. This is the most direct solution, and for most dogs it produces noticeable improvement within 2–4 weeks of full transition.

Step 2: Consider Hydrolysed Protein

If your dog's food intolerance or sensitive gut is preventing efficient protein absorption, hydrolysed protein goes further — the protein is pre-broken into small-chain peptides before your dog eats it, maximising absorption and minimising fermentation. Our Hydrolysed Digestive Care Dog Food combines 95% protein digestibility with TruPet™ postbiotic — directly targeting both causes of faecal odour simultaneously.

Step 3: Support the Gut Microbiome

A healthy gut microbiome produces fewer odour-causing fermentation byproducts. Postbiotics, prebiotics and probiotics all help restore a healthy balance of gut bacteria. TruPet™ postbiotic has been shown to increase beneficial Bifidobacterium and reduce faecal phenol and indole concentrations in dogs.

Step 4: Eliminate Dietary Triggers

If your dog has a food intolerance, the trigger ingredient will cause increased fermentation every time it is eaten. A grain free diet removes common irritants. If symptoms persist on grain free food, the issue is likely protein-related — see our guide: My Dog Is on Grain Free but Still Has Digestive Problems.

When Smelly Poo Is a Sign of Something More Serious

In most cases, particularly smelly dog poo is a dietary problem. However, see your vet if the smell is accompanied by:

• Blood in the stool
• Dramatic changes in stool consistency or frequency
• Weight loss despite a good appetite
• Very pale, greasy or very large stools (possible sign of EPI or malabsorption)
• Signs of pain or discomfort

What Our Customers Say

“I can honestly say the difference in smell within a fortnight was remarkable. Our Springer's poo used to clear a room — now it's completely manageable. The whole family noticed it without me even mentioning it.”

“My vet couldn't explain why Rufus's poo was so bad. I switched to the hydrolysed food after reading about protein digestibility and within three weeks the smell had more than halved. Wish I'd found this sooner.”

“German Shepherd poo has a reputation for a reason. I thought it was just the breed. Turned out it was the food. Switched to Ultimate Pet Foods and it's like a different dog. My neighbours have even commented.”

Frequently Asked Questions

Why does my dog's poo smell so bad?

The most common cause is undigested protein fermenting in the large intestine. When dog food has poor protein digestibility, the unabsorbed protein is fermented by gut bacteria, producing phenols, indoles, ammonia and hydrogen sulphide — the compounds responsible for particularly strong faecal odour.

Can changing dog food reduce faecal odour?

Yes — often dramatically. Switching to a food with higher protein digestibility means less undigested protein reaching the large intestine to ferment. Our Hydrolysed Digestive Care Dog Food achieves 95% protein digestibility and includes TruPet™ postbiotic, shown to directly reduce odour-causing compounds in dog faeces.

How long does it take for a food change to reduce smelly poo?

Most owners notice a significant improvement within 2–4 weeks of fully transitioning to a more digestible food. Always transition gradually over two weeks to avoid a temporary digestive upset from the food change itself.

Is very smelly dog poo a sign of illness?

Occasionally — particularly smelly or very abnormal stools can indicate malabsorption, EPI, IBD or infection. If the smell is accompanied by blood, dramatic changes in consistency, weight loss or signs of pain, see your vet. For consistently smelly but otherwise normal stools, diet is almost always the cause.

Does grain free dog food reduce poo smell?

It can help if grain sensitivity is contributing to fermentation. However, if protein digestibility is the main issue, grain free alone may not be enough. A hydrolysed dog food addresses the root cause more directly.

---

Looking for the full picture? Read our Complete Guide to Dog Digestive Health.