Proteins in the animal body cannot be formed from other nutrients – carbohydrates and fats, since they lack nitrogen. Therefore, proteins are considered essential nutrients. Animals obtain the proteins necessary for the body in the form of crude feed protein. Each protein molecule is composed of amino acids. It was found that animals do not need protein as such, but amino acids in a certain amount and ratio. Proteins and amides of animal feed consumed by enzymes of the gastric, intestinal juices and pancreatic juice are digested and broken down in the digestive tract to amino acids, which are absorbed into the small intestine and enter the bloodstream. In ruminants, a significant part of the protein and other nitrogen-containing compounds of the feed are cleaved in the rumen to ammonia. Part of it is used by the rumen microflora to synthesize the protein of your body. The rest of the ammonia is absorbed and enters the liver, where it turns into urea; some of it is excreted from the body, and the rest in the composition of saliva again returns to the scar. Microflora, together with the feed protein remaining undigested, is digested in the subsequent sections of the digestive tract, and is broken down to amino acids, which are absorbed in the small intestine and enter the bloodstream.
Part of the amino acids enters the liver and is synthesized into a reserve protein. The main part of the amino acids goes to the tissues and is used for the synthesis of cellular tissue proteins characteristic of animals of the corresponding species. Along with the synthesis of protein in cells, it breaks down. The intensity of protein metabolism is determined by the amount of nitrogen introduced into the body with food and excreted from it with feces and urine.Protein metabolism is regulated by the central nervous system through the endocrine glands.