He digestive system Of birds Begins at the peak or mouth and includes different important organs and endings such as the sewer.
Although it has similarities with the digestive apparatus of mammals and reptiles, the digestive tract of birds is characterized by special organs such as the crop and gizzard (Stevens & Hume, 1995).
Digestive system of a bird. Recovered image from: alejandrajaimeperez.wordpress.com
The digestive system of any animal is of vital importance for the processing of the food that the animal consumes. Through the digestive tract birds can absorb all the nutrients their bodies need to grow, maintain and reproduce.
As the birds do not have teeth, the foods digested by them are decomposed mechanically and chemically in the digestive system. That is, different digestive enzymes and acids are released to be able to digest the food and the organs involved in the process are crushed and mixed, ensuring maximum absorption of nutrients during the process.
Because of their high metabolic requirements, birds should consume more food than other vertebrates in proportion to their size. The digestive process makes possible the release of nutrients contained in food. Likewise, it makes possible the absorption and uniform distribution of these nutrients in the body of the bird.
The deep understanding of the functioning of the birds digestive system allows industries such as poultry to be sustainable. Similarly, the care of birds in captivity becomes viable thanks to the knowledge of their digestive system (Svihus, 2014).
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Parts that form the digestive system of birds
1- Peak or Mouth
Birds use their beak to feed themselves. All food entering the bird's body first passes through the beak. Birds have no teeth, so they can not chew food.
However, salivary glands can be found inside the beak, which serves to moisten food, allowing them to be swallowed easily.
The saliva that is inside the beak contains digestive enzymes as amylase Which serve to initiate the process of digestion of food. Birds also use their tongue to push the food to the back of the beak to swallow it (Jacob & Pescatore, 2013).
The esophagus is a flexible tube that connects the beak to the rest of the bird's digestive tract. It is responsible for bringing food from the mouth to the crop and from the crop to the proventriculus.
The buche is a protrusion of the esophagus located in the region of the neck of the bird. Swallowed food and water are stored in this bag until they can pass to the rest of the digestive tract.
When the crop is empty or almost empty, it sends signals of hunger to the brain for the bird to eat more food.
Although the digestive enzymes secreted in the beak begin the process of digestion, in the crop this process is quite slow, since this organ serves as a temporary storage place for food.
This storage mechanism was developed in birds that are typically hunted by other animals, but need to move in the open to find food.
In this way, birds can consume a considerable amount of food quickly and then move to a safer place to digest such food.
Occasionally, the crop may be affected by obstruction or impaction. This happens when the bird takes a long period of time without consuming food and suddenly swallows a large amount.
When this occurs, the food can initiate 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.
An inflamed swab may also block the trachea or air outlet, causing birds to die from suffocation.
The esophagus continues after the crop and connects it with the proventriculus. This organ is known as the glandular stomach of birds where the primary digestion begins.
Hydrochloric acid and digestive enzymes such as pepsin are mixed with ingested food and begin to break down more efficiently. At this time, the food has not yet been ground.
5- Ventricle or Gizzard
The ventricle or gizzard is an organ of the digestive system of both birds and reptiles, earthworms and fish.
It is usually referred to as the mechanical stomach, because it is composed of a pair of strong muscles with a protective membrane that act as if they were the teeth of the bird.
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.
Sometimes birds can consume small rocks inside the food. These are usually softened in the proventriculus and ground in the gizzard.
Generally, ground rocks remain in the gizzard until their size is small enough to pass through the rest of the digestive tract.
When a bird ingests a sharp object, such as a tack or a staple hook, the object may be trapped in the gizzard. These objects can pierce the gizzard when your muscles begin to move quickly.
Birds that present damage to the walls of the gizzard, begin to suffer from malnutrition and eventually die (Loon, 2005).
6 - Small Intestine
The next step of digestion occurs in the duodenum and the nutrients released by the food are mainly absorbed in the lower part of the small intestine.
The duodenum receives the digestive enzymes and bicarbonate from the pancreas and bile of the liver to counteract the effect of Hydrochloric acid From the proventriculus.
The digestive juices produced by the pancreas are mainly related to the digestion of proteins. Bile is a major cleansing agent in lipid digestion and absorption of fat-soluble vitamins such as A, D, E, and K.
The lower part of the small intestine is composed of two parts, which jejunum and the ileum . He Meckel's diverticulum Marks the end of the jejunum and the beginning of the ileum. This diverticulum is formed during the embryonic stage of the birds (Bowen, 1997).
The mint consists of two blind pockets where the small and large intestine are attached. Some traces of water contained in the digested food are reabsorbed at this point.
Another important function of the mint is the fermentation of the food remains that have not yet finished being digested. During the fermentation process, the mint produces fatty acids and the eight Vitamins B (Thiamine, riboflavin, niacin, pantothenic acid, pyridoxine, biotin, folic acid and vitamin B12).
The mint is located very close to the end of the digestive tract, however, it still absorbs some nutrients available in the food (Farner & King, 1972).
8- Large Intestine or Colon
Although the name suggests 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 remaining remains of water present in the digested material.
In the sewer, residues of digestion are mixed with waste from the urinary system (urea). Birds usually expel fecal matter from the digestive system along with uric acid crystals resulting from the process of the excretory system.
As birds do not urinate, they expel debris from uric acid in the form of a whitish, creamy paste.
The feces of the birds can indicate in which state of health they are. The color and texture of the fecal material indicates the conditions under which the digestive tract is located.
In the cloaca also converge the reproductive system of the birds. When a female lays an egg, the vagina is folded over the surface of the egg, so that the cloaca can be opened without contact with faeces or urine (PoultryHub, 2017).
Intestinal microflora of birds
In both the small and large intestines it is normal to find populations of microorganisms beneficial to digestion (bacteria and yeasts, among others), these small organisms are called microflora. These populations are, in part, responsible for successful bird digestion.
When a bird breaks the egg at birth, its digestive system is in the sterile state. When a baby bird is raised by its mother, it obtains all the microorganisms coming from the microflora of it.
When a bird is incubated in captivity, it does not have the possibility of obtaining the microflora of its mother and the caregivers must prepare a mixture of microorganisms to mix them with the food of the bird.
Bird intestinal diseases usually occur when the balance of the microflora is altered by external organisms. As a result birds may suffer from enteritis or inflammation of the intestines.
Enteritis can be detected when the bird has diarrhea, consumes more water than normal, loses appetite, is weak, has slow growth or loses weight.
- Bowen, R. (September 7, 1997). Colostate. Retrieved from Digestive Physiology of Birds: vivo.colostate.edu.
- Farner, D. S., & King, J. R. (1972). Digestion and the digestive system of birds. In D. S. Farner, & J. R. King, Avian Biology, Volume 2 (pp. 352-359). New York and London: Academic Press.
- Jacob, J., & Pescatore, T. (2013). Avian Digestive System. Animal Sciences, University of Kentucky.
- Loon, R. (2005). Digesting the Meal. In R. Loon, Birds: The Inside Story (pp. 152-153). Cape Town: Struik Publoshers.
- (February 1, 2017). Poultry Hub. Obtained from Digestive system: poultryhub.org
- Stevens, C. E., & Hume, I. D. (1995). The digestive system of fish, amphibians, reptiles and birds. In C. E. Stevens, & I. D. Hume, Comparative Physiology of the Vertebrate Digestive System (pp. 40-42). Cape Town: Cambridge University Press.
- Svihus, B. (2014). Function of the digestive system. The Journal of Applied Poultry Research, 306-314.