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Digestive processes and juices in chickens: how digestion works

Castilian, Minorcas, white Face, Andalusian, J W Ludlow, 1914

Digestive process:

Digestion includes all the physical and chemical processes through which the food ingested by the hen is broken down and made soluble, so that it can be absorbed by her body.

This includes physical processes such as

Swallowing.
Peristalsis: It is called the movement of successive contractions along the stomach and intestines, and the breaking action of the gizzard.
Chemical processes: as the solvent action of the water.
Enzymes.
Bacteria.

Generally, the digestion of the food is not complete.

The undigested portion of the food will be expelled in the stool.

Digestive juices:

The most important part digestion is the action of ferments, or enzymes, that are fluids secreted by the walls of the digestive system, or by the body's annexes, already described, and containing water, enzymes, and other products needed to be able to make water-soluble foods, which are

Saliva: The saliva is a digestive juice important in the chicken, because it is secreted in very small amounts.

It contains amylase, which breaks down a small amount of starch into maltose. Saliva also helps moisten the food we eat.

Gastric juice: The gastric juice is made up of water, hydrochloric acid, and enzymes such as pepsin and renin. It is an acid reaction and acts primarily on the decomposition of proteins.

Juices intestinal: Intestinal juices are composed of water, bile, pancreatic juice, and intestinal juice. Bile emulsifies fats and aids in their digestion.

Pancreatic juice contains several enzymes.

Trypsin: that acts on proteins.
The amilopsina: that acts on the starch.
The esteapsina: that acts on the fat.
Trypsin: an element that breaks down proteins and invertases (produced by yeasts), which act on sugars.

Digestion of nutrients:

Carbohydrates: Carbohydrates must be broken down into simple sugars so that they can be absorbed by the hen's body.

The thialin in saliva and the amylopsin in pancreatic juice act on starch, breaking it down first into dextrin and then into maltose.

The intestinal lining breaks down maltose and similar sugars, converting them into simple sugars such as glucose.

The fiber is only digested in small degree by the birds. It is believed that the decomposition of the fiber is produced by bacterial fermentation, mainly in the cecum.

Proteins: Proteins must be broken down into amino acids so that the hen can absorb them. This process produces a number of byproducts.

Protein-derived products, all of which are insoluble, are mostly metaproteins and coagulated proteins.

Secondary protein derivatives—the enzymes in gastric juice—act on proteins, causing them to break down; these derivatives are soluble and consist mainly of proteoses, peptones, and peptides.

The trypsin of the pancreatic juice acts similarly, but the peptones and peptides are hydrolyzed, in addition to partially into amino acids.

Protein digestion is completed by erepsin in the intestinal juice, which breaks down proteoses, peptones, and peptides into amino acids.

Fats: All fats have to split themselves into fatty acids and glycerin so that they can be absorbed by the body of the chicken.

Bile, which contains alkaline salts, saponifies, emulsifies, and dissolves fats and fatty acids. Steapsin in the pancreatic juice then breaks down fats into fatty acids and glycerin.

Differences in a chicken's digestion compared to other animals:

The viscera of birds they are less complex than those of mammals. For example, in regard to the genitourinary system, in birds is not stored urine in a bladder, but that is poured directly into the sewer, where they mix with the stool.

The end product of protein breakdown—which is uric acid in chickens—appears as whitish crystals in their feces; in mammals, the end product is urea, which is soluble.

A notable characteristic of the chicken is the relatively short length of its large intestine; the ratio of the large intestine to the small intestine is approximately one to thirty. In higher domestic animals, this ratio is approximately one to three or four.

The general structure of the digestive system in the hen indicates rapid digestion. The short length of the digestive tract is a carnivore's nature, while the nature of the ration and the crushing of full food in the gizzard are characteristics of an herbivore.

Birds produce very little saliva, and the concentration of thialin is very low. In ruminants, saliva production is high, but the concentration of thialin is not particularly high. The digestibility of various foods varies among different animal species. The nutrient that hens digest most efficiently is non-nitrogenous extract; following in order of digestibility are fat, protein, and fiber.

Other domestic animals cannot digest the fiber in significant proportions: ruminants in the belly, or herbal; horses and pigs in the large intestine.

Chickens digest fiber to only a very limited extent, and in any feed, it rarely exceeds 15%. In thin-hulled oat varieties, a higher proportion of fiber is digested than in thick-hulled varieties.

The digestion of fat also varies in the different foods, like chicken. The fat of corn is much more digestible than those of oat, barley, or wheat.

Apparently, the digestibility of the food is not affected by the crushing of the same. Cooking increases the digestibility of some nutritious principles, especially starch. The digestibility of the protein is lower in the food poor in these principles.

Time required for food to pass through the digestive tract:

The time that is needed for food to pass through the digestive system depends a lot on the type of food and the state of the chicken.

Studies have concluded that this period is 4 hours for laying hens and growing birds. For non-laying hens, this period was extended to 8 hours; for hens broody or lluecas, 12 hours approximately.

Food was first observed in the stool 2 to 3 hours after ingestion; grains appeared 2½ to 3½ hours later.

As we mentioned above, the food accumulates in the crop of the bird. The time required for the food to leave the crop depends on the type and condition of the same. The disappearance of the grains of the crop of chickens occurs in periods of time similar to the different types of grain, while the oatmeal is retained in the crop for more time than the corn and the wheat. In contrast, the same whole corn remains longer in the maw than the corn grits and this more than the ground corn.

Cooked oats pass through the crop faster than dry oats; mash mixtures spend less time in the crop than dry mixtures. In experiments conducted at Cornell, the following percentages of ingested grains were found in the crop:

After 4 hours, 70% to 80%.
After 8 hours, 55 to 65%.
After 12 hours: 35% to 45%.
After 16 hours: 25 to 35%.
After 20 hours: 10 to 20%.
After 24 hours: 0 to 10%.

In experiments conducted in Germany, corn took 50 to 70 hours to pass through a hen’s digestive tract, wheat took 102 hours, and oats took 120 hours.

Assimilation:

The absorption of nutrients in chickens occurs primarily in the small intestine. Some absorption also takes place in the large intestine and the cecum. For nutrients to be absorbed, they must be in liquid form.

The nutritious principles of the food are absorbed by the intestinal epithelium through a process similar to osmosis. The sugars in the type of glucose, amino acids, and mineral matter can penetrate directly into the bloodstream. The fatty acids and the glicerinas penetrate into the lymphatic system, whose vessels empty into the blood system.

Bibliography:

Dyce, K. M., Sack, W. O., and Wensing, C. J. G., 1991. Veterinary Anatomy. Ed. Pan-American.

Ede, D. A., 1965. Anatomy of birds. Ed. Acribia.

Grasse, P. P., 1980. Zoology. Vol. 4: Vertebrates. Reproduction, biology, evolution, and systematics. Ed. Toray-Masson.

Grifols, J. and Molina, R. 1994. Manual of clinical exotic birds. Ed. Grass-Iatros.

Natural History, 1984. Vol. 1. Ed. Ocean-Institute Gallach.

King, G. M. and D. Custance. Colour atlas of vertebrate anatomy: The Pigeon. Pp.: 5.1— 5.17. Ed. Blackwell Scientific Publications.

Krahmer, R., and Schröeder, L. 1979. Anatomy of the domestic animals. Ed. Acribia.

McClelland, J., 1992. Atlas in color of the anatomy of birds. Ed. inter-American.

Nickel, R., 1977: The Anatomy of the Domestic Birds. Ed. Paul Parey.

Sandoval, J., 1976. Veterinary Anatomy. Ed. Modern Printing Press (Córdoba).

Schwarze E. 1980. Compendium of Veterinary Anatomy. Volume V: Anatomy of birds. Ed. Acribia.

Shively, M. J., 1993. Veterinary anatomy, basic, comparative, and clinical. Ed. Manual Moderno.

Sturkie PD, 1967. Physiology of Avian. Ed. Acribia.

Dr. Francisco Gil Cano.

Professor H. Aguinaga.

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