Worldwide poultry production has increased significantly over the past fifty years to accommodate rising demand. Broiler chicks grow rapidly and typically receive diets high in protein or amino acids . It is common practice in the poultry industry to provide varying diets during the growing period.

The concept of ideal protein

Amino acids which are essential cannot be synthesized by the animal. They must therefore be provided by feed. When the supply of one of these essential amino acids does not meet the animal’s requirement for this amino acid, it is said to be limiting. This limiting amino acid is limiting the potential growth of the animal. Once the limiting amino acid is covered via the feed, the next amino acid will become limiting (second limiting amino acid, third limiting amino acid, etc). There is no sense in giving more of the non-limiting amino acids (more protein) to the animal. As long as the limiting amino acid is not supplied, the animal cannot use the other amino acids (protein).

Therefore the goal is to know the exact requirement of the animal for every essential amino acid in order to supply this amount to the animal via the diet. This is what is called the ideal protein concept. In practical diets, normally lysine is the first limiting amino acid. Therefore we always express the requirement of all essential amino acids as a ratio to lysine.

Protein is an essential constituent of all tissues of animal body and has major effect on growth performance of the bird . A better understanding of the nutritional requirements of amino acids allows a more precise nutrition, offering the possibility for the formulator to optimize the requirement of at least minimum levels of crude protein by essential amino acids requirements, generating better result and lower costs for the producer . Feeding high amino acid density diets improves feed conversion and increases weight gain and breast meat yield of broiler chickens . Methionine + cystine (total sulfur amino acid = TSSA) perform a number of functions in enzyme reactions and protein synthesis. Methionine is an essential amino acid for poultry and has an important role as a precursor of cystine.

Methionine is usually the first limiting amino acid in most of the practical diets for broiler chicken . Lysine is often one of the limiting amino acids in broiler diets. As such, it used as the reference amino acid to which all other essential amino acids are rationed in the ideal amino acid pattern . Therefore, it is crucial to obtain an accurate Lys and Met + Cys requirement to support optimum growth of fast-growing commercial broilers.

Many poultry nutritionists use the levels recommended by the National Research Council as a guideline in establishing their own amino acid requirements. In practical poultry diets methionine is the first limiting amino acid followed by lysine. Therefore, supplementation of methionine and lysine to practical poultry diets provides a means for increasing the efficiency of protein utilization, and as a result N excretion will be reduced. After these amino acids, threonine and in young chicks also glycine may often become limiting by reducing the dietary level of protein. Lysine is an essential amino acid closely associated with body protein deposition potential. It is considered the second limiting amino acid for broilers fed diets based on corn and soybean meal.

Dietary crude protein (CP) requirements are somewhat of a misnomer as the requirement is based on the amino acids content of the protein. Once digested and absorbed, amino acids are used as the building blocks of structural proteins (muscle, skin, ligaments), metabolic proteins, enzymes, and precursors of several body components. Because body proteins are constantly being synthesized and degraded, an adequate amino acid supply is critical to support growth or egg production.

In poultry, 22 amino acids are needed to form body protein, some of which can be synthesized by the bird (non-essential), whereas others can not be made at all or in sufficient quantities to meet metabolic needs (essential). Essential amino acids must be supplied by the diet, and a sufficient amount of non-essential amino acids must also be supplied to prevent the conversion of essential amino acids into non-essential amino acid. Additionally, if the amino acids supplied are not in the proper, or ideal, ratio in relation to the needs of the animal, then amino acids in excess of the least limiting amino acid will be deaminated and likely used as a source of energy rather than towards body protein synthesis. This breakdown of amino acids will also result in higher nitrogenous excretions.

The best way to reduce N in poultry excreta is to lower the amount of CP that is fed by supplementing diets with amino acids. Reductions in the non-essential amino acid pool, coupled with supplying a more “ideal” amino acid profile in the diet can substantially increase the efficacy of overall N retention by the bird. On a practical basis, however, bird performance can be hindered by these lower CP diets due to a number of factors that tend to be associated with dietary CP and amino acid reductions. Formulation based on bird amino acid requirements rather than CP can minimize N excretion by simply reducing total dietary N intake. For example, Ferguson et al. (1998) demonstrated with broilers that litter N could be reduced more than 16% when dietary CP was reduced by 2%, while maintaining similar levels of dietary amino acids. Reduced Dietary Protein Reducing the amount of CP and excess amino acids being fed is the most obvious method to curb N excretion and the amount of ammonia (NH3) that can be formed and volatilized.

Surplus of protein negative for the animal health

Amino acids can be supplied by the diet via feedstuffs (cereals, soybean meal, etc). The amino acid pattern (ratio of essential amino acids to lysine) in protein feedstuffs is not always (mostly not) in line with the requirement of the animal (the ideal protein). Protein feedstuffs are too low in the first limiting amino acids. If we would supply all essential amino acids via raw materials we would have to supply very high levels of crude protein. Because not all protein will be used, the surplus will be excreted by the animal. This surplus of protein is very negative for the animal health (surplus protein will be used by pathogenic bacteria in the large intestine and can cause intestinal disorders) and has a negative impact on the environment (nitrogen excretion).

Low crude protein, optimal supply of amino acids

On the one hand we want a good supply of protein (amino acids) to cover all the needs of the animal, but on the other hand we want to formulate diets with a crude protein level as low as possible, in order to ensure optimal health for the animal and spare the environment. This is possible with feed-use amino acids. These free amino acids enable the formulator of the diet to supply the exact amount of every single amino acid, in order to cover the need of the animal in every life stage. On the other hand the crude protein can be kept on a very low level, which is ideal for the animal and beneficial for the environment as well.

Knowing the requirement of the animal

A lot of research is done to determine the exact requirement of every essential amino acid for the animal. The requirement is depending on the animal species (pigs, poultry) and on the life stage. The need for amino acids for piglets is for example different from the one of the growing pig or the lactating sow. Also other factors, like the health status, may affect the requirement.

Biological functions of protein

As stated above, protein is needed for enhancing growth, egg production, immunity, and adaptation to the environment. In addition, there are other biological functions which are attributed to specific amino acids. Lysine, for example, has an important role in improving carcass quality of chickens by supporting formation of type IIb fibre which hold smaller amounts of fat and have low cooking loss (loss of nutrients in the cooking water), as opposed to type IIa fibres which are formed in the carcasses in case of lysine deficiency. Thrionine, on the other hand, has significant metabolic roles and helps regulation of GI secretions and endogenous losses, thereby improving digestibility of nutrients and preventing digestive disorders. Other amino acids, such as methionine, may partly compensate for a deficiency of choline or vitamin B12 by providing needed methyl groups. Also, the amino acid tryptophan may alleviate niacin deficiency through metabolic conversion to niacin. However, these conversion processes are of theoretical interest only, as it would be poor economics to satisfy a vitamin deficiency by addition of relatively more expensive amino acids.


For broiler chickens, diets are often formulated to contain 22% protein for the starter feed and 19% for the finisher feed, with a metabolisable energy value in the order of 3.3 ME/Kg. Chickens may respond differently to the increased protein level in the diet, depending mainly on the protein quality and the amino acid profile thereof. With low quality protein having inadequate and/or imbalanced amino acids, increasing dietary protein in this case will have no effect on performance in terms of growth, feed efficiency and carcass traits, but may rather lead to high mortality and leg problems, particularly in the finishing phase. Addition of the first limiting amino acids in this case will, therefore, be necessary and will result in an increased productive output in the bird. This effect, however, will continue until the maximum genetic potential of the bird is reached or the amino acids are no longer limiting.

On the other hand, when high quality protein is fed, the increased level of dietary protein by 2-3% above the recommended level will in this case improve growth rate, feed efficiency and carcass quality and the supplemental amino acids will not have any sound effect on performance. In one study, supplementation of diets having conventional crude protein levels with essential amino acids did not restore growth to that of the higher protein diet. The chickens fed on diets with conventional protein level also had increased abdominal fat which was not reduced by adding essential amino acids but was reduced when the level of high quality protein was increased (Fancher and Jensen, 1989).

The concept of dietary protein level and quality in relation to performance also holds true with the layers. In one study, white leghorn chickens were fed corn-SBM diets containing 11, 14, 17, 18 or 20% crude protein from hatching to 16 weeks of age and then fed 17% crude protein layer diet. Body weights were reduced by feeding 11 or 14% crude protein and the pullets were slightly slower coming into production compared to those fed 17 or 20% crude protein. Egg weight was also depressed by feeding 11 or 14% crude protein diets, probably due to the smaller body weight at 16 weeks of age. These findings may, again, vary depending on the quality of protein fed, as indicated earlier.

Amino acids

The essential amino acids

  • Arginine.
  • Isoleucine.
  • Histidine.
  • Leucine.
  • Lysine.
  • Methionine plus cystine.
  • Phenylalanine plus tyrosine.
  • Threonine.
  • Tryptophan.
  • Valine.

Dl- Methionine

DL-Methionine is the first limiting amino acid for poultry. If the natural methionine content of poultry feed is low, it must be augmented with supplements. It is vital as a structural material for protein synthesis and methyl group donor in the process of creatine synthesis, ethanolamine, noradrenaline etc. Methionine prevent from fat collecting in liver and its fat regeneration. In the lack of methionine the appetite goes down, growth slows. Feeding methionine is white crystal powder with light smell, liquefiable in the hot water, alcohol and acids. There are methionine 98% in perfect preparation.

L-Lysine Sulphate

L-Lysine Sulfate feed additive used for enrichment and balance the rations of agricultural animals with lysine. 

Along with lysine in a preparation there are other substances that enhance its nutritional value :

carbohydrates, mineral salts, organic acids, more than 10% of other amino acids. L-Lysine Sulfate has greater exchange energy than lysine in hydrochloride form. The use of L-Lysine Sulfate in mixed feed production is economically viable and environmentally sound, and increase economic efficiency of production.

L- Lysine Monohydrochloride

L-Lysine belongs to a group of essential amino acids. It is required for the regulation of nitrogen, carbohydrates, and also for synthesis of nucleotides, chromoproteids, promotes healthy growth of young agricultural animals. It affects the formation of erythrocytes and deposition of calcium in the bones and the absorption of phosphorus. Also it has positive effect on the hematopoietic function of the bone marrow and the state of the nervous system. This amino acid is used in the manufacture of mixed feed for pigs and poultry.

L- Tryptophan

This amino acid is a precursor to many physiologically active compounds of serotonin, tryptamine, nicotinic acid. Tryptophan is required for normal reproduction, for the growth of animal and dairy production. The drug is a white, crystalline substance containing not less than 70% of L-tryptophan.

L- Threonine

Perfect threonine is white crystal powder. It’s the second limitative amino acid in the protein of wheat, barley and sorghum. The most effect can be reached in pig breeding. Lack of threonine is in growing stock and poultry.


L-Valine is one of the 20 proteinogenic amino acids, found on almost all known proteins. One of the main components in the growth and synthesis of body tissues. Together with leucine and isoleucine is the source of energy in the muscle cells and prevents the reduction of the level of serotonin. Its use in manufacture of mixed feeds for pig and poultry production is economically beneficial and safe.

Dr. Rajesh Kumar Singh

Poultry Consultant - 9431309542

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