Protein deficiency in poultry diets leads to weakness and poor performance, particularly affecting carcass yield due to the reduced availability of essential amino acids required by the body.

To meet the nutritional needs of poultry for optimal performance, varying levels of protein are recommended at different stages of their life. These protein levels are necessary to provide the amino acids and peptides that form the building blocks of proteins, which play crucial roles in the body’s structure, including ligaments, organs, muscles, skin, feathers, bones, and various metabolic functions.

Protein deficiency in poultry diets results in weak and poorly performing birds, primarily due to a reduction in the necessary amino acids.

Amino acids are vital not only for protein production but also for essential metabolic functions like enhancing the immune system and improving digestive functions in poultry.

Poultry experts emphasize that amino acid requirements are the most crucial nutritional factor to consider due to their economic value and metabolic importance.

Dietary protein is metabolically significant as it can provide essential amino acids and convert into glucose, fatty acids, and certain vitamins through metabolic processes.

t is common for poultry farmers and technicians to encounter recommendations to reduce or even eliminate protein (soy) from the diet during illnesses. This recommendation is often made by veterinarians, yet the reason behind it might not be clear to everyone.

Reducing dietary protein, rather than eliminating it, is beneficial because the bird needs various amino acids to produce white blood cells, antibodies, and antigens specific to the disease. However, high protein levels can strain the kidneys and liver, sometimes leading to conditions like gout, which can exacerbate the illness.

There are 22 amino acids found in body proteins, all of which are essential. These amino acids are categorized into three groups:

1- Essential Amino Acids

2- Semi-Essential Amino Acids

3- Non-Essential Amino Acids

Amino acids that cannot be synthesized by the body are classified as essential. Semi-essential amino acids are synthesized at slower rates, and non-essential amino acids can be synthesized by the body. About nine amino acids are considered essential due to the lack of necessary enzymes for their synthesis.

Considering that approximately 65-75% of production costs in poultry farming are feed-related, and protein can be introduced as the most significant part of the feed cost, the best way to reduce feed cost is to reduce protein levels in the diet. However, reducing protein according to the aforementioned discussions will impair poultry health, growth, and production.

On the other hand, environmental scientists and researchers have concluded that the excess protein portion in feed, if excreted by poultry, also disrupts and pollutes the environment. Ultimately, through nitrogen entering drinking and food sources, human health is also compromised.

Therefore, reducing protein levels in poultry diets has benefits, two of which were mentioned above. Now the main question is how to reduce protein levels in the diet without harming the bird.

The only solution to this issue is to add some synthetic amino acids to reduce protein levels in the diet while providing the necessary amino acids for the bird.

In other words, nutritionists and diet formulators who previously balanced the diet based on crude protein must now meet these needs based on total amino acids.

In the next step, nutritionists and diet formulation researchers provide the birds’ needs based on ideal amino acids and ileal digestibility (SID).

Considering that many of these amino acids are available and used in the livestock and poultry feed industry, in Iran, only methionine, lysine, and threonine amino acids are available.

To meet the amino acid needs of chicks in the early days of life due to the high need for valine amino acid, which performs many functions in the bird’s body (including issues related to chicks’ immunity titers), other protein sources such as soybean meal and even wheat and corn gluten must be used.

Since soybean is a rich source of potassium and due to the limitation of soybean consumption in day-old chicks and the incomplete digestive system of chicks, the flock experiences diarrhea, leading to leg problems, increased ammonia and its accumulation in the hall, feed waste, and inadequate growth, which is one of the initial amino acid supply problems. Using synthetic valine can solve this problem, but unfortunately, due to the high cost of feed in Iran, it is not cost-effective.

The difference in broiler chicks’ needs can be seen in Tables 1 and 2.

Ideal Protein

Ideal protein is a combination of essential amino acids that meet maintenance and growth needs with minimal deficiency or excess. In this context, lysine is chosen as the standard amino acid, and other amino acids are determined as a percentage of lysine.

Reasons for selecting this amino acid include:

1- Abundant information about lysine,

2- Lysine only participates in protein synthesis and has no role in metabolic structures,

3- Lysine is the second limiting amino acid in corn-soy diets.

Ideal protein has led to more precise diets with reduced feed costs and less nitrogen excretion in poultry nutrition.

Ileal Digestibility (SID)

Feed materials used by living organisms undergo digestion and absorption, with nutrients being absorbed through the intestinal wall and bloodstream.

Not all nutrients in feed materials are absorbed by the body, and the portion that is absorbed is called digestible. The final absorption station in birds’ intestines is the end of the small intestine (ileum), where absorption is considered complete.

Therefore, the digestible portion of a feed material is referred to as the ileal digestible portion (SID).

Accordingly, all synthetic amino acids have a certain purity and different digestibility levels, referred to as ileal digestible amino acids. All diets are formulated to reduce costs and metabolic burden on the bird’s liver and accurately balance the diet.

In such diets, balancing amino acids is crucial.

Limiting Amino Acid

The amino acid in the feed with the lowest amount relative to the bird’s needs is called the first limiting amino acid.

The next amino acids, with concentrations in the feed lower than the bird’s needs compared to other amino acids, are known as the second limiting amino acid. The same principle applies to other amino acids.

All amino acids above the first limiting amino acid are only considered as energy sources and may even negatively affect production.