Amino acids (aa) are basic units that form proteins. These perform several vital functions in addition to protein synthesis, such as tissue renewal (endogenous losses, losses of the epidermis, exchange of feathers and scales).
Classification of amino acids
There are several amino acids, however we are only interested in 20, they are classified as essential, non-essential, conditionally essential and limiting amino acids.
In swine and poultry we have 10 essential amino acids, with arginine being conditionally essential only in one phase of the pigs and its supplementation from 3 to 21 days of life of the animals is extremely important, where they produce only 60% of the requirement.
Essential amino acids are those in which the animal does not synthesize or produce in sufficient quantity to meet its requirements. Therefore, non-essentials are synthesized by animals and can be synthesized from other amino acids by the process of transamination, as in the case of cysteine that is synthesized from methionine, consequently, if methionine is not ideally supplemented, cysteine will become an essential amino acid. The limiting factors refer to the limitation of a certain amino acid in an ingredient or diet. Diets based on corn and soy are limiting in lysine, methionine, threonine and tryptophan. When this is a limiting factor, its lack in the diet determines the excess or lack of another, which in this case will be oxidized, or else, it will cause amino acid imbalance.
For broilers the first and second limiting amino acids are Met and Lis respectively, in pigs first it is Lis and then Met. Corn, the main energy source, is limiting in Lysine and tryptophan, soy in methionine, so one must pay attention to the correct supplementation of these.
Balanced diets based on CP result in amino acid imbalance, with excess of some and lack of others, in addition to loss of performance with energy expenditure in the excretion of excess nitrogen in the form of uric acid and recurrent environmental pollution.
In this context comes the concept of ideal protein, proposed by Mitchell in 1964, where it is defined as the exact balance of amino acids capable of meeting the requirement for maintenance and production, without excess and without fail, that is, balanced.
The application of the ideal protein brings economic and environmental advantages, such as a reduction in the level of crude protein and less excretion of N, since it is expected that all amino acids will be used. The reduction of crude protein helps the animal in terms of thermal comfort, because the digestion of the protein has a large caloric increase – CI.
However, the reduction of crude protein without taking into account the proper supplementation of amino acids can cause a deficit of non-essential amino acids, requiring attention and care.
Sulfur Amino Acids
Methionine and Cysteine are the only sulfur amino acids. Met is the first limiting amino acid for chickens due to its limitation in feeds based on corn and soybeans as previously mentioned, and also due to its high requirement, since they are of great importance for maintaining feathers.
Met is still the largest donor of methyl radicals (Ch3) in the body for the synthesis of choline, betaine, carnitine, polyamines, epinephrine and melatonin, these molecules with great participation in the growth and development of the animal. It is still linked to lipid metabolism, and its deficiency leads to greater deposition of adipose tissue. Therefore, when properly supplemented in chicken feed, it promotes a positive action on tissue protein concentration, carcass yield, breast yield and reduction of abdominal fat content.
Cysteine, on the other hand, contributes to the formation of collagen and keratin, acting in the maintenance of feathers. Its synthesis takes place from methionine. The requirements for met-cis are higher when the animal is young, and decreases with increasing age.
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