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An understanding of the avian digestive system is essential for developing an effective and economical feeding program for your poultry flock and for recognizing when something is wrong and taking necessary actions to correct the problem.

The digestive system of any animal is important in converting the food the animal eats into the nutrients its body needs for growth, maintenance, and production (such as egg production). An animal’s body breaks down food through both mechanical and chemical means. In many animals, the mechanical action involves chewing; however, because birds do not have teeth, their bodies use other mechanical action. The chemical action includes the release of digestive enzymes and fluids from various parts of the digestive system. After being released from food during digestion, nutrients are absorbed and distributed throughout the animal’s body.

The chicken has a typical avian digestive system. In chickens, the digestive tract (also referred to as the gastrointestinal tract or GI tract) begins at the mouth, includes several important organs, and ends at the cloaca.
Beak/Mouth
As with most birds, a chicken obtains feed by using its beak. Food picked up by the beak enters the mouth. Chickens do not have teeth, so they cannot chew their food. However, the mouth contains glands that secrete saliva, which wets the feed to make it easier to swallow. Also, the saliva contains enzymes, such as amylase, that start the digestion process. The chicken uses its tongue to push the feed to the back of the mouth to be swallowed.

Esophagus
The esophagus is a flexible tube that connects the mouth with the rest of the digestive tract. It carries food from the mouth to the crop and from the crop to the proventriculus.

Crop
The crop is an out-pocketing of the esophagus and is located just outside the body cavity in the neck region (see Figure 3). Swallowed feed and water are stored in the crop until they are passed to the rest of the digestive tract. When the crop is empty or nearly empty, it sends hunger signals to the brain so that the chicken will eat more.

Although the digestive enzymes secreted in the mouth began the digestion process, very little digestion takes place in the crop—it is simply a temporary storage pouch. The crop evolved for birds that are typically hunted by other animals but need to move to the open to find feed. These birds can consume relatively large amounts of food quickly and then move to a more secure location to digest that food.

Occasionally, the crop becomes impacted, or backed up. This problem—called crop impaction, crop binding, or pendulous crop—can occur when a chicken goes a long time without feed and then eats too much too quickly when feed is available again. Crop impaction also can occur when a chicken free ranges on a pasture of tough, fibrous vegetation or eats long pieces of string. With crop impaction, even if a chicken continues to eat, the feed cannot pass the impacted crop. The swollen crop also can block the windpipe, causing the chicken to suffocate.