Page 742 - The Veterinary Care of the Horse

The stages of digestion

MOUTH
VetBooks.ir Horses use their incisor (front) teeth and lips to take food into the mouth. Here it is

thoroughly chewed and mixed with saliva. The mucus content of saliva lubricates the passage

of food down the oesophagus into the stomach. When food material becomes lodged in the
oesophagus, it causes the condition known as choke. The teeth must be kept in good order so

that food is sufficiently broken down before entering the stomach.

STOMACH

The stomach of the horse is relatively small with a capacity of some 7–8 litres. The horse
should therefore be fed little and often to avoid digestive upsets. Horses are unable to vomit

because there is a powerful muscular sphincter between the stomach and the lower end of the
oesophagus. Food reflux occurs only when very high pressure builds up in the stomach. This

can occur in horses with grass sickness and obstructions of the small intestine.

The lining of the stomach is divided into glandular and non-glandular parts. The
glandular region secretes digestive enzymes and acid. Horses exposed to high levels of stress
and inappropriate feeding may suffer from gastric ulcers.

SMALL INTESTINE (DUODENUM, JEJUNUM, ILEUM)

The food passes out of the stomach into the duodenum, where it is mixed with pancreatic
enzymes and bile secreted by the pancreas and liver. The digestive enzymes break down

protein, carbohydrate and fat. Digestion and absorption occur along the length of the small
intestine, which is more than 20 m (65 ft) in the average Thoroughbred-sized horse.

The food material is moved along by contraction of smooth muscle in the gut wall. The
waves of muscular activity are called peristalsis.

LARGE INTESTINE (CAECUM, COLON)

Undigested food and fibre now enter the large intestine where bacteria continue the digestion
of protein, carbohydrate and fat. They also:

• ferment and digest cellulose

• form essential amino acids
• produce B vitamins and vitamin K.

The bacterial population varies according to the nature of the diet. Horses fed on grass and
hay will have a different microbial population from those fed on high-concentrate diets. If the