Chicken | Vet In Training

Chicken intestines

Chicken intestines (Photo credit, Caroline Barrett)

This week I’ll inform you on a bird’s intestines, namely, the chicken’s. A chicken’s intestines occupy the posterior (or caudal) part of the body. The small intestine is long and relatively uniform in shape and size. Interestingly, there is also no dividing line between the middle (jejunum) and final section of intestine (ileum). The jejunum has loose coils around the mesentery. Also, it has thin walls so its content appears green. The short colon lies ventral to the synsacrum (fused lumbar vertebrae) and opens into the cloaca (passage for fecal material) runs ventral to (below) the vertebrae and terminates in the coprodeum (deepest part of the cloaca). Amino acids and glucose can be absorbed here. Two caeca (pouches at the begining of the large intestine) from the ileocaecal junction run with the ileum caudally. And they extend towards the liver then fold back on themselves. The mesentery runs between the caeca then on towards the ileum. It often contains dark colored material. There are three parts of each caecum. It is where the bacterial breakdown of cellulose occurs. If the intestines are healthy, chyme from the caeca are emptied a few times per day. A bird’s digestive system is a lot different than a mammal’s. Which would be expected, as they are foul.

To see more chicken anatomy, click here.

Chicken stomach (photo credit nutrenaworld.com)

Chicken Stomachs

This week we’ll look at the chicken stomach. Bird stomachs are different from mammal stomachs in many ways. Today we will be looking at the Crop, the Proventriculus, and the Gizzard. The crop is an out-pocketing of the esophagus and is located just outside the body cavity in the neck region. Any swallowed food and water is stored in the crop until it is time to pass it on 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 salivary glands of the mouth secrete the digestive enzyme amylase, very little digestion actually takes place in the crop, it is simply a temporary storage pouch. The proventriculus (also known as the ‘true stomach’) is the glandular stomach where digestion begins. As with human stomachs, hydrochloric acid and digestive enzymes (like pepsin) are added to the food here. At this point however, the food has not yet been ground up. The term ‘proventriculus’ is used since it comes before the ‘ventriculus’ or gizzard, with ‘pro’ being the Latin term meaning before. And finally, the gizzard. The gizzard, or ventriculus, is a part of the digestive tract unique to birds. It is often referred to as the ‘mechanical stomach’. It is made up of two sets of strong muscles which act as the bird’s teeth. Consumed food and the digestive juices from the salivary glands and the proventriculus pass into the gizzard for grinding, mixing, and mashing, which is aided by the small stones or grit the bird consumes. These stones remain in the gizzard until they become ground into pieces small enough to pass through to the rest of the digestive tract. The stones/grit are weakened by the acidic environment created in the proventriculus and then are ground into tiny pieces by the strong muscles of the gizzard. This is how chickens can eat a lot of hard seeds and not get digestive issues like humans. Ultimately, Chicken stomachs are designed to ingest the bugs and seeds which chickens need to survive. If any part of the stomach did not work correctly, the chicken might die. Which just goes to show how intricate the whole system is.