por What is the digestive system of birds?
He digestive system of the birds It is the system by which birds feed and absorb nutrients. It starts at the beak and includes different organs. Although it has similarities with the digestive systems of mammals and reptiles, that of birds is characterized by having special organs, such as the crop and the gizzard.
The digestive system of any animal is of vital importance for the processing of food. Through the digestive system, birds can absorb the nutrients that their bodies need to grow, maintain and reproduce.
Since birds do not have teeth, ingested food is broken down mechanically and chemically in the digestive system. That is, different digestive enzymes and acids are released to be able to digest food, and the organs involved in the process grind and mix them, guaranteeing maximum absorption of nutrients in the process.
Due to their high metabolic demands, birds must consume more food than other vertebrate animals, in proportion to their size.
The deep understanding of the functioning of the digestive system of birds allows industries such as poultry to be sustainable. In the same way, the care of birds in captivity becomes viable thanks to the knowledge of this system.
Parts of the digestive system of birds
Beak
Birds use their beaks to feed. All the food that enters its body goes through the beak first. Birds don’t have teeth, so they can’t chew food.
However, inside the beak can be found glands that secrete saliva that serves to moisten food, allowing it to be swallowed easily.
The saliva inside the beak contains digestive enzymes, such as amylase, which are used to start the process of digesting food. Birds also use their tongues to push food to the back of their beaks so they can swallow it.
Esophagus
The esophagus is a flexible tube that connects the beak to the rest of the digestive tract. It is responsible for carrying food from the mouth to the crop and from the crop to the proventriculus.
Maw
The crop is a projection of the esophagus located in the neck region of the bird. Swallowed food and water are stored in this bag until they can pass into the rest of the digestive tract. When the crop is empty or nearly empty, it sends hunger signals to the brain so the bird eats more food.
Although the digestive enzymes secreted in the beak start the digestion process, in the crop this process is quite slow, since it serves as a temporary storage place for food.
This storage mechanism evolved in birds that are typically hunted by other animals, but need to move in the open to find food.
In this way, they can consume a considerable amount of food quickly and then move to a safer place to digest it.
On some occasions, the crop can be affected by clogging or impact problems. This happens when the bird has not eaten food for a long time and suddenly eats a large amount.
When this happens, the food can start a process of decomposition inside the crop and make the bird sick. The crop can also become clogged when the bird consumes large pieces of plant material that block the passage of food to the rest of the digestive system.
A swollen crop can also block the windpipe, or air outlet, causing birds to suffocate.
proventriculus or glandular stomach
The esophagus continues after the crop and connects it with the proventriculus. This organ is known as the glandular stomach, where primary digestion begins.
Hydrochloric acid and digestive enzymes such as pepsin mix with ingested food and begin to break it down more efficiently. At this time, the food has not yet been ground.
Gizzard
The gizzard is an organ of the digestive system of both birds and reptiles, earthworms and fish. It is usually known as a mechanical stomach, as it is made up of a pair of strong muscles with a protective membrane that act as if they were the bird’s teeth.
The food consumed by the bird and the digestive juices from the salivary glands and the proventriculus pass to the gizzard, where everything will be ground and mixed.
Birds can sometimes swallow small stones with their feed, which will help grind everything up in the gizzard. Generally, these stones, which will break up in the process, remain in the gizzard until they are small enough to pass through the rest of the digestive tract.
When a bird ingests a sharp object, such as a tack or stapler hook, the object can get caught in the gizzard. These objects can pierce you when your muscles start to move quickly.
Birds with damage to the gizzard walls begin to suffer from malnutrition and eventually die.
Small intestine
The next step of digestion occurs in the duodenum and the nutrients released by food are absorbed mainly in the lower part of the small intestine.
The duodenum receives digestive enzymes and bicarbonate from the pancreas and bile from the liver to counteract the effect of hydrochloric acid from the glandular stomach.
Digestive juices produced by the pancreas are primarily concerned with protein digestion. Bile is an important cleansing agent in the digestion of lipids and the absorption of fat-soluble vitamins, such as A, D, E, and K.
The lower section of the small intestine is made up of two parts, the jejunum and the ileum. Meckel’s diverticulum marks the end of the jejunum and the beginning of the ileum. This diverticulum forms during the embryonic stage of birds.
Mint
The ceca is made up of two blind pouches where the small and large intestines join. Some traces of water contained in the digested food are reabsorbed at this point.
Another important function of the mint is the fermentation of food remains that have not yet finished digesting. During the fermentation process, the mint produces fatty acids and the eight B vitamins (thiamin, riboflavin, niacin, pantothenic acid, pyridoxine, biotin, folate, and vitamin B12).
The mint is very close to the end of the digestive tract, however some nutrients available in the food are still absorbed in it.
Large intestine or colon
Although its name indicates that the large intestine is larger than the small intestine, it is actually shorter. The main function of the large intestine is to absorb the last remnants of water present in the digested material.
Sewer
In the cloaca, waste from digestion mixes with waste from the urinary system (urea). Birds generally expel fecal matter from the digestive system along with uric acid crystals resulting from the process of the excretory system.
Since birds do not urinate, they expel uric acid waste in the form of a creamy, whitish paste. Bird feces can indicate the state of health they are in. The color and texture of fecal matter indicates what condition the digestive tract is in.
The reproductive system of birds also converges in the cloaca. When a female lays an egg, the vagina folds over the surface of the egg so that the cloaca can be opened without coming into contact with feces or urine.
Intestinal microflora of birds
In both the small and large intestine it is normal to find populations of beneficial microorganisms for digestion (bacteria and yeast, among others). These microorganisms are called microflora. In birds, these populations are partly responsible for successful digestion.
When a bird hatches from an egg at birth, its digestive system is in a sterile state. When a chick is reared by its mother, it gets all the microorganisms from her microflora.
When a bird is hatched in captivity, it has no chance of obtaining its mother’s microflora and keepers must prepare a mixture of microorganisms to mix with the bird’s food.
Intestinal diseases of birds generally occur when the balance of the microflora is disturbed by foreign organisms. As a result, birds can suffer from enteritis, or inflammation of the intestines.
References
Bowen, R. Colostate. Retrieved from vivo.colostate.edu.
Jacob, J., & Pescatore, T. Avian Digestive System. Animal Sciences, University of Kentucky.
Digestive system. Retrieved from poultryhub.org.
Svihus, B. Function of the digestive system. The Journal of Applied Poultry Research.