Chicken Digestive System 101

You know the old adage “As scarce as hen’s teeth” meaning something is rare because, of course, chickens don’t have any teeth. Have you ever wondered how they process all kinds of food that ultimately gets excreted as soft poop? If you’re like me then your curiosity has been piqued.

I won’t bore you with all the scientific names and long drawn out explanations for what happens at each stage along the way. Instead here’s the quick-and-dirty version, which will give you a little insight into what your chicken can eat and how it gets processed.

Port of entry is the beak: the perfect tool for pecking feed, grains, grass and insects. Chickens are omnivores – they eat meat (grubs, worms, and even mice and snakes if they catch them) and vegetation (grass, weeds, fruits and veggies). Saliva and digestive enzymes are added as the food moves from the mouth into the esophagus.

Next stop: the crop. First time chicken owners sometimes panic when they see a large lump at the base of their neck. It’s an expandable pouch where food can remain for up to 12 hours. The crop can become infected with candida, a yeast infection (sour crop), or food can get stuck there (impacted crop). A bird that survives an impacted crop may lose its muscle tone and develop a pendulous crop.

The food trickles from there into the bird’s stomach (proventriculus and gizzard) where digestive enzymes are added to the mix and food is ground up. This is why chickens don’t need teeth: the muscular part of the stomach uses grit (tiny, hard pebbles, sand or crushed oyster shells) to grind everything into more digestible particles. If your birds are free-ranging you don’t need to offer them grit, but if they are confined provide them free access to a bowl of oyster shells. I’ve got a 1200 square feet pen with plenty of small pebbles, but I still give them oyster shells.

Food then passes into the small intestine, where nutrients are absorbed. The residue moves through the caeca, a sack along the lower intestinal tract, where bacteria help break down undigested food. Then on to the large intestine, which absorbs water and dries out indigestible foods.

Chickens don’t urinate. They lose most excess moisture through breathing. Uric acid forms a white cap on poop, both of which pass through the cloaca and exit the chicken through the vent, the external opening of the body.

Chicken poop is high in nitrogen; let it age and use it to amend your garden beds.

A quick synopsis of the digestive system:

• Mouth: In this case, beak.
• Esophagus (Gullet): Transports food from the mouth to the stomach.
• Crop: A pouch in the esophagus used to store food temporarily before moving it on to the stomach.
• Stomach (Proventriculus/Gizzard): The main place where food is broken down. There are two parts: the proventriculus for storage and the gizzard, which uses grit for grinding food into smaller pieces.
• Small Intestine: Aids in digestion and nutrient absorption. Composed of the duodenum, jejunum and ileum.
• Liver: The largest organ in the body. Metabolizes carbohydrates, fats and proteins.
• Caeca: Bacteria help break down undigested food passing through the intestine. The caeca turn into the large intestine, which connects with the cloaca.
• Large Intestine: Functions primarily to absorb water, dry out indigestible foods and eliminate waste products.
• Cloaca: Where the digestive, urinary and reproductive systems meet.
• Urinary System: Consists of two kidneys that filter waste from blood, which pass through two ureters to outside the body via the cloaca/vent.
• Vent: The end of the line: the external opening of the cloaca that passes waste (and eggs) outside the body.

Read more about sour, impacted and pendulous crop issues here.