How Dog Digestion Works
How your dog's digestion works
From bowl to garden in about a day: what happens at each stage, why a dog's stomach is smaller than you think, and how to tell from the stool which part is unhappy.
The mouth
Dogs barely chew. Their teeth tear and crush, saliva adds a little amylase, and food is swallowed in lumps. That is normal, and it is why kibble size matters more for the mouth than for digestion: the real breakdown starts further down.
The stomach
Strongly acidic, which kills bacteria and starts protein digestion. It is also small. A dog's stomach holds around two to three per cent of body weight, roughly 100 to 150 g of wet food per kilo, or 22 to 33 g of dry, per sitting. Fill it beyond that and the meal sits, ferments and comes back up. Two or three smaller meals suit most dogs better than one large one, and small, frequent meals are the first thing vets reach for when a stomach is upset.
The small intestine
Where the work happens. Enzymes from the pancreas break down protein, fat and starch, and the gut wall absorbs the results along with most of the water. When the small intestine is the problem, the signs are large, foul-smelling stools with undigested food, rumbling, sometimes vomiting, and weight loss that comes on quickly.
The large intestine
Absorbs the remaining water and houses the gut bacteria, which ferment fibre into short-chain fatty acids that feed the gut lining and keep harmful bacteria in check. When the large intestine is the problem, the signs are the opposite: small amounts, very often (more than five times a day), with mucus and sometimes fresh red blood, but rarely vomiting or weight loss.
Why the distinction matters. Small-bowel diarrhoea usually responds to a day's rest and a bland, low-fibre diet. Large-bowel diarrhoea needs the cause found, and often responds to more fibre rather than less. Telling your vet which pattern you are seeing shortens the diagnosis.
What a healthy result looks like
Two to three stools a day, firm and formed, medium to dark brown, picked up cleanly. A highly digestible food produces less, because more is absorbed. The seven-point chart shows the full range and what each score means.
What upsets it
Feeding errors are the most common cause of all. A switch made over four days rather than four hours, meals sized to the stomach, and treats counted as food prevent most of the upsets that reach our inbox. The switching schedule.
What helps it
Digestibility first: a food that is absorbed rather than passed through. Then fibre of the right kind: fermentable fibres such as beet pulp, apple pomace and psyllium to feed the bacteria, cellulose to give the stool form. Then consistency: the same food, in the same amounts, at the same times. The gut bacteria are set up for the food they know, and every change is work for them.
When something does go wrong, digestive disorders in dogs covers what to do and when it is a vet visit.
Based on "Gastrointestinal disease in the dog: feeding tips" by Pascale Huber, veterinarian, and "On the trail of the runs" by Cornelia Günther, veterinarian, Happy Dog veterinary team.
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