Digestion & Excretion

Chickens are omnivores meaning that they can eat almost anything including meat (usually worms, grubs, insects, and occasionally small mice), vegetation (grass, weeds, and other plants), and fruit (berries and tree fruit).

In this section, we will follow the journey of food along the chicken digestive tract as it gets ingested, broken down, absorbed, and removed along with other waste products from the body in the form of droppings.

Check out our Poultry Nutrition section for advice on making sure your birds are getting a complete and balanced diet.

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Digestive Tract

The chicken digestive tract can be divided into 10 main anatomical parts that help to break down food using mechanical digestion (physically grinding up the food into smaller particles) and chemical digestion (producing enzymes and acids to dissolve food particles) so that nutrients can be absorbed into the body and any undigestible waste can pass out through the other end.

We’ll discuss each part briefly and included links to the Virtual Chicken YouTube channel, which has some great videos to help you further understand what goes on where.

Chickens pick up their food with their beak and then swallow it whole because do not have teeth or hard palate (bony roof of our mouth) to help them break down the particles. They produce saliva to help make the food easier to swallow.  Although saliva does contain a small amount of digestive enzymes, it doesn’t have that much impact on starting to digest the food at this stage.  Chickens have a tongue at the back of their mouth that helps push food into the oesophagus.  They can swallow very hard objects or very stringy objects like long grasses or twine, which may cause problems if they get stuck further down the digestive tract. 

You may have heard that some poultry keepers trim the beak in chicks to prevent them from causing injuries when they peck other birds. We do not recommend this for your flock because it can your birds pain and prevent them from eating normally.

The oesophagus is a 20 to 35cm flexible tube that connects the mouth with the crop. The lining of the oesophagus produces some mucus to help food slide down easier.

The crop is a small pouch at the end of the oesophagus that sits outside the main body cavity at the base of the neck.  The main purpose of the crop is to temporarily store food.  When chickens were living in the wild, this allowed them to eat large amounts of food quickly out in open areas and then move to safer locations away from predators to digest it.  Some food will start passing out of the crop within the first 30 minutes, but it usually takes about 2 to 4 hours to completely empty at which point the chicken will start to feel hungry again.  Some food can remain for up to 12 hours. 

When the crop is empty, you normally won’t be able to see or feel it easily.  However, if your chicken has just eaten a big meal or if they are having a problem with the crop that’s stopping food from passing through normally, it may feel very large or firm.  The most common causes of crop impaction are either (1) eating fibrous material that gets stuck and stops over food passing through or (2) if chickens eat too much too quickly after going without food for a long time.

The proventriculus is similar to our stomach and is where the digestive process really begins.  The lining of the proventriculus makes hydrochloric acid (HCl) and pepsin, which start to dissolve the food.  Food doesn’t spend much time here passing quickly through into the gizzard.

The gizzard (or ventriculus) is a strong muscular organ that contracts to break down large food particles and helps to mix the digestive enzymes throughout the food mass. When chickens forage in their environment, they will eat small stones or pebbles that become trapped in the gizzard to help grind down food until they have become small enough to pass through the rest of the digestive tract. Backyard chickens usually need to be supplemented with insoluble grit (small stones or pebbles that do not easily dissolve with the enzymes and acids in the digestive tract) since they may not be able to pick up enough in their environment, particularly if they are kept in enclosed runs or on pasture. The thick lining of the gizzard helps protect from the acids made by the proventriculus.  It is important to prevent your chickens from eating sharp objects like metallic wire, nails, and glass shards since these can poke a hole in the gizzard, which can damage it enough to eventually cause your chicken to die.

The small intestine in the longest part of the digestive tract and has three main sections.

  1. Duodenum – This is where most of the chemical digestion occurs from enzymes that are released into the duodenum by the pancreas and from bile that is the released by the liver through the gall bladder. The enzymes mainly target proteins while bile targets fats.
  2. Jejunum – This is where more mechanical digestion and absorption occurs. Contractions in the intestinal wall help churn things around and allow absorption of key nutrients into the blood where they can pass to the liver for further process.
  3. Ileum – This last segment is where water and bile as well as other nutrients are absorbed.

The ceca are two blind pouches sitting where the small intestine and large intestine join.  The ceca contain a lot of bacteria that help break down any remaining undigested food and produce B vitamins. Most of the remaining water absorption also occurs here.  The ceca empty their contents 2 to 3 times per day producing cecal droppings, which are more mustard-brown coloured and worse smelling than the normal greenish-brown droppings you would expect.

The large intestine is a very short segment about 6 cm long where the final water is absorbed before the droppings are released.

The cloaca (coming from the Latin word meaning sewer) is a common channel that is also hooked into the reproductive tract and kidneys allowing droppings, eggs, and uric acid to leave the chicken’s body.

The vent refers to the opening from the cloaca to the outside world and is what you will see if you look at the backside of your chicken.

Overall, it takes about 4 to 8 hours for food to completely pass through the 2 to 2.5m long digestive tract depending on the breed of chicken and what they have been eating.  Once the nutrients have been absorbed into the blood, the liver further processes them into substances that are needed for survival and circulates back into the blood so they can reach the right cells. 

Urinary Tract

The kidneys then filter the blood to remove additional waste products and help the body to maintain a good fluid and electrolyte balance. The kidneys sit at the top of the body cavity on either side of the spine.  Since chickens do not have bladders, the urine the kidneys produce (a thick, pasty white substance containing mostly uric acid from breaking down nitrogen) travels through the ureters into the cloaca.  Interestingly, it gets pushed back into the large intestine where any remaining water can be absorbed and then it is usually passed out as a white cap on top of the faecal droppings. 

Droppings

Normal Droppings

In healthy backyard chickens, the normal faecal component of the droppings should be firm and either brown or green depending on how much plant material they are foraging during the day. It might be much more colourful if they have been fed strongly pigmented fruits like blueberries or vegetables like beetroot.

The urates will appear as the white cap covering about 30% to 50% of the faeces.  Sometimes you may also see a small amount of clear fluid which is liquid urine. Consuming a lot of watery fruit will result in more liquid urine being produced. A healthy chicken will pass droppings about 12 to 15 times per day including at night.

Cecal Droppings

Caecal droppings are produced about 2 to 3 times per day. They are usually light brown to mustard coloured with a particularly bad smell.

Broody hens who are sitting on the nest for a long time period will retain droppings instead of producing  them every hour or so throughout the day.  When she does leave the nest, she will produce a very large amount of droppings that also smell particularly bad.