The digestive system of the chicken - general structure

The fowl's digestive system breaks down ingested food to basic components by mechanical and chemical means. These basic components are then absorbed and used throughout the body. A knowledge of the digestive process greatly assists in understanding the nutritive requirements of the fowl.

The digestive system begins at the mouth and ends at the cloaca. Intervening organs/parts include the oesophagus, crop, proventriculus, gizzard, duodenum, small intestine, paired caeca and large intestine. Other organs vital to digestion are the liver and pancreas.

Mouth

Armed with a beak for gathering and pecking, food is moistened with saliva containing a starch-reducing enzyme and then swallowed without chewing.

Oesophagus - crop - proventriculus - gizzard

The oesophagus is a flexible tube which carries food from the mouth to the crop. The crop is a temporary storage pouch at the base of the neck that sends the hunger signal to the brain. The oesophagus then traverses the chest cavity to carry food to the proventriculus where food is mixed with acids and other digestive enzymes. Retention time here depends on the activity of the crop and gizzard. Grit in the gizzard, combined with strong muscular action, grinds the food into a mash.

Small intestine

The small intestine starts at the exit of the gizzard with the duodenal loop and ends at the ileo-caecal-colon junction.

Food in the duodenum is neutralised by the addition of more enzymes excreted by the pancreas. These enzymes break down protein. Also added here is bile produced by the liver and stored in the gall bladder. Bile aids in fat digestion.

The products of digestion are absorbed from the small intestine and carried to the liver primarily for remanufacture into body tissue or to provide energy.

Caeca

The caeca are two blind-ended tubes which provide space for fermentation. Here undigested food particles are subjected to microbial breakdown. The caeca normally contain a mustard to dark-brown froth which is excreted about once every day.

Large intestine

This part of the gut is very small in the fowl and serves as a further absorption site especially for water.

Cloaca

The cloaca or vent is a chamber common to the digestive and urogenital systems. It is responsible for the elimination of faeces, urine and the passage of eggs or seminal fluid.

Pancreas

A yellow organ lying in the duodenal loop. Also produces insulin for the control of blood-sugar level.

Liver

The largest organ in the body, divided into two lobes, produces bile and is a major detoxification organ.