How Does a Dog Digest Food?

The easiest way to understand canine digestion is to follow a meal from beginning to end.

Mouth

Digestion begins when the dog eats.

Teeth mechanically reduce food into smaller pieces and mix it with saliva.

Unlike some species, dogs rely relatively little on salivary digestion of starch. The main importance of chewing and saliva is therefore physical processing, lubrication and preparation for swallowing.

Oesophagus

Once swallowed, food travels down the oesophagus.

Muscular contractions called peristalsis move the swallowed material towards the stomach.

The oesophagus is principally a transport organ rather than a major site of digestion or nutrient absorption.

Stomach

The stomach stores a meal and mixes it with gastric secretions.

Hydrochloric acid creates a highly acidic environment.

This helps denature proteins and supports the activity of pepsin, an enzyme involved in protein digestion.

The stomach also mechanically churns food, gradually turning it into a semi-liquid mixture known as chyme.

Material is then released progressively into the small intestine.

Duodenum

The duodenum is the first section of the small intestine and an important transition point.

Here, acidic stomach contents mix with secretions from the pancreas, liver and intestinal wall.

Bicarbonate helps raise the pH from the very acidic conditions of the stomach, while digestive enzymes continue breaking nutrients into forms that can eventually be absorbed.

Pancreas

The pancreas is not part of the hollow digestive tract, but it is central to digestion.

It releases digestive enzymes into the small intestine.

These include enzymes involved in the breakdown of proteins, fats and carbohydrates.

The pancreas also supplies bicarbonate, helping create conditions in which intestinal digestive enzymes can function.

Liver and gallbladder

The liver produces bile.

Bile is stored and concentrated in the gallbladder before being released into the small intestine.

Bile helps disperse dietary fat into much smaller droplets, increasing the surface area available to digestive enzymes.

This supports the digestion and subsequent absorption of fats.

Jejunum

The jejunum forms a substantial part of the small intestine and is a major site of nutrient absorption.

The inner surface of the intestine contains folds, villi and microscopic microvilli that dramatically increase the available surface area.

Digested carbohydrates, amino acids, fatty acids, vitamins, minerals and other nutrients can then cross the intestinal lining and enter circulation.

Ileum

The ileum is the final section of the small intestine.

Absorption continues here, and certain nutrients and bile components that have not already been absorbed can be recovered.

By the time material leaves the small intestine, a large proportion of the nutrients that can be digested and absorbed by the dog should already have been processed.

Large intestine

Material that reaches the large intestine contains water, minerals, undigested dietary components, microbial biomass and compounds produced earlier in the digestive process.

Water and electrolytes are absorbed.

At the same time, the large intestine contains a dense microbial ecosystem.

Microorganisms can ferment some substrates that escaped digestion in the small intestine, producing a range of metabolites.

Rectum and anus

The final part of the digestive tract stores and eliminates faecal material.

Stool therefore represents the end product of digestion, absorption, microbial activity and water recovery throughout the gastrointestinal tract.