Overview

Gut health relates to the whole of the digestive tract, which officially starts in the mouth and ends with, surprisingly, the rear end, or more biologically accurate, the rectum and anus.

In humans, digestion begins in the mouth. We physically break down food with our teeth, and salivary enzymes get to work.

This is slightly different in the dog; the structure of their teeth means they are equipped for ripping and tearing, and then swallowing larger chunks of foods.

Digestion in dogs actually starts in the stomach!

The stomach is like a washing machine; it physically churns food around, but it also releases enzymes, acid, and hormones to break the food down into a usable form.

The stomach also releases hydrochloric acid, more commonly known as stomach acid from the parietal cells. This highly acidic environment causes proteins to lose their characteristic folded structure which exposes the bonds of the protein. Stomach acid also inhibits the growth of many microorganisms which is helpful to prevent infection.

In the stomach, food is turn into a substance known as ‘chyme’, and this moves to the small intestine, which is full of tiny, carpet like projections. These projections allow for nutrient absorption and in short, they allow whatever is in the small intestine to reach circulation.

The pancreas feeds into the small intestine and is like the factory of the digestive system; producing enzymes and hormones to further digest the chyme.

The liver makes and secretes bile acids which emulsify fats, meaning they can subsequently be digested. Bile acids are stored in the gallbladder for release.

We then get to the large intestine which has four main functions:

• Hydration
• Housing the microbiome
• Helping nutrients get where they need to go (nutrient absorption)
• Housemaid (compacts the waste to be excreted)

If we are looking to support gut health, we need to support it from the mouth down!

Mouth

From the moment a tooth erupts it is exposed to food, saliva, and bacteria. Periodontal disease occurs when there is a buildup of bacteria in the mouth, which forms plaque until eventually, this hardens to form tartar which can sit in the gum line causing inflammation, known as gingivitis.

Left untreated, further harm occurs which results in periodontitis, where teeth fall out and damage can occur to the surrounding bone.

Smaller breeds are statistically more likely to suffer with periodontal disease, as are brachycephalic (squashed face) type breeds. Their teeth are often closer together which means food and bacteria can more easily get stuck. Bacteria found in the mouth of your dog can be released into the circulatory system, which then travels through the body.  It has been found to damage cardiac tissue causing endocarditis (infection and inflammation in the heart).

This leads us nicely into the microbiome found in the mouth.

There is a collection of microbes found in the mouth; they pose a first line of defence against ingested potentially harmful pathogens, but they also play a role in metabolising certain nutrients. These would be deemed the ‘beneficial’ bugs; the issue is when potentially harmful bugs outnumber the beneficial bugs.

So, caring for the mouth cavity is just as important as caring for the gut, and colonisation occurs at and shortly after birth – and certainly within the teething period!  Dental hygiene is therefore crucial; avoiding ultra-processed foods, along with high-sugar foods and treats (those containing high-fructose corn syrup).

Opportunities to chew are a great way to maintain dental hygiene as chewing stimulates saliva which produces anti-bacterial agents, helping to keep the mouth clean. Not only this but the abrasion that occurs during chewing helps to scrape deposits off the teeth.

• Raw bones reduce mouth bacteria by 79%
• Daily brushing reduces it by 70% and
• Marketed dental chews reduces it by 54-60%   [1]

Stomach

The production of stomach acid is crucial for sufficient digestion to occur. Sadly there are a number of medications that can reduce the production, including antihistamines and proton pump inhibitors.

Pancreas

The pancreas is a small organ that sits behind the small intestine and the stomach. It helps to digest food but also secretes hormones that help to regulate blood sugar levels.

The pancreas is the factory of the digestive system. It releases a range of enzymes and hormones that further help to break down food as it makes its way through the system. It produces lipase which helps to break down fat, protease which helps to break down protein and amylase which helps to break down starch. As we know, canine saliva contains low levels of amylase, but we are relying on the pancreas to produce the bulk to do the job.

The pancreas feeds these enzymes into the small intestine.

There is an age-old question around fat causing pancreatitis in dogs, but this is largely data extracted from human information. There are associations between hyperlipidemia (high circulating fat levels in the blood) and pancreatitis in humans, but the exact relationship is not known in dogs (or cats for that matter). Some studies have demonstrated a link, some have not.

For example, one study found that 26% of pancreatitis cases also had hyperlipidemia, yet other studies that have experimentally induced pancreatitis haven’t altered lipid levels at all.

Obesity is the main risk factor for pancreatitis, but there are other noted correlates, and a poorly functioning digestive system is one of them.

Partially or under-digested foods can start to run amok in the digestive system; calling the immune system to action to sort it all out. The inflammatory response is a one of the immune systems most prized tools. The pro-inflammatory response is countered by an anti-inflammatory response and so the body sorts itself out.

Pancreatitis is an inflammatory process and there are considerations that the damage is a result of an imbalanced inflammatory response.

But there is also the consideration that if food isn’t sufficiently being digested in the stomach, then it is again placing an unusual burden on the pancreas.

The other risk factor that it gaining attention is pharmaceutical induced pancreatitis, more commonly linked to corticosteroids. The interest first arose in dogs being treated for intervertebral disc disease. Higher reports of pancreatitis were seemingly occurring in those dogs treated with corticosteroids. Yet there are those who criticise this could simply be genetic – IVDD has a genetic risk, as does pancreatitis.

That said, there are studies which highlight that increasing doses of steroids may increase the risk of acute pancreatitis. [2]

Liver

The liver processes blood and the substances found within it. In a healthy animal, blood draining from the intestines passes immediately through the liver for nutrients to processed and for toxic compounds to be removed. The blood then re-enters main circulation.

The detoxification of toxic compounds falls into three phases.
Phase I directly neutralises chemicals and changes them into new metabolites. These are then processed by phase II enzymes. This is known as the conjugation phase, which in short, liver enzymes attach small chemicals to the toxin. There are many ways in which this is done, it all depends on the type of chemical the liver is trying to manage.

Phase I results in high levels of reactive oxygen species so antioxidant levels are key in modulating potential damage.

Phase II is nutrient demanding and sufficient levels of key vitamins and minerals like vitamin A, C, E, B1, B2, B3 and iron are essential. There has also been data to suggest that foods like dandelion can support the enzymatic detoxification pathway.    

Phase III is the elimination phase.

For optimal excretion of toxins through the digestive system, gut health is vitally important.  Maintaining the gut barrier is key for gut health along with supporting motility.

Gut Barrier

The physical barrier consists of tight junctions which form a selective permeable seal between adjacent epithelial cells. These tight junctions are regulated by a range of compounds, including cytokines. As we know cytokines are involved in the inflammatory response, and certain cytokines have been seen to cause increase TJ permeability. Modulation of the inflammatory response is therefore crucial in gut barrier integrity.

Furthermore, the gut barrier also consists of a mucosal layer.
The mucus layer is the very first line of physical defence that external molecules encounter when they arrive in the gut lumen, it prevents bacteria from directly contacting the epithelial cells, along with toxic substances and digestive enzymes.

There is a natural turnover of mucous within the GI tract, the issue arises when there is more degradation than synthesis and secretion; it gets a little thin on the ground.  This is where mucosal supplementation can be supportive.

Selective bacteria can degrade mucous as an energy source, but within the same strand, bacterial presence is needed for the mucosal barrier to develop its full functionality. Balance is key.
Stress is also seen affect the integrity of the gut barrier, with early life stress impairing the development of mucosal barrier function.

Allergies & sensitivities

Generally, allergies and sensitivities are associated with poor barrier function. Cells sit tightly together, but when cell integrity fails, under digested food particles and pathogens see their opportunity and sneak out into circulation.

The immune system spots these particles – realises they shouldn’t be there, so mounts a response.  Inflammation is a key part of this response.

When the barrier remains compromised, more particles sneak through and so we end up in a chronic state of inflammation; in our dogs we notice this in chronic skin issues and digestive discomfort.  

Dermatological signs include:

• Pruritus (dry, itchy skin)
• Erythema (rashes)
• Secondary infections (yeast/bacterial)
• Alopecia (hair loss)

• Vomiting
• Diarrhoea
• Frequent defecation
• Colitis/IBD/IBS

• Genes
• Microbiome dysbiosis (imbalance)
• Long-term use of certain medications
• Toxins
• Environmental exposure
• Stress
• Diet choice – high levels of saturated fat, refined and processed foods are linked with compromised barrier function

So if we want to support gut health, we have to start at the top and ensure we are supporting each organ or system as we go down.

In summary - how to support a healthy gut

Promote dental hygiene

Offer opportunities to chew, not only to remove harmful bacterial but chewing activates the parasympathetic nervous system which is the counter to the “typical” stress response.

Support liver function

Appropriate and efficient toxin elimination is crucial.

Support gut integrity

Slippery elm is brilliant at protecting the mucosal barrier function in gastrointestinal illness.

Modulate inflammatory responses

Omega-3 fatty acids are seen to help modulate the inflammatory response and improve outcomes in hyper-inflammatory conditions.

Flaxseed oil provides a rich source of omega-3 ALA.

Offer a nutrient dense diet

Offer a nutrient dense diet, low in refined and processed products

Reduce stress

Reduce stress where possible and feed a stress relieving supplement.