The role of amino acids in the diet of poultry

When formulating diets for poultry, it is important to carefully select the ingredients of the feed to ensure the correct balance of amino acids. The diet of poultry during their growth should be rich in proteins, fats, carbohydrates, vitamins, and minerals. The organism of poultry is not capable of synthesizing vitamins and amino acids in sufficient quantities necessary for high productivity on its own, and an imbalance in the diet negatively affects the growth, development, and efficient productivity of poultry. A team of experts from Vitagro Nutrition has developed three lines of premixes: Vitamix Classic, Vitamix Premium, and Vitamix Profit for effective feeding, health, and rapid growth of poultry.

Vitamix premixes are formulated taking into account the needs for biologically active substances of broilers and contain the complete complex of vitamins, minerals, amino acids, micro- and macro-elements that activate the enzymatic, hormonal, and immune systems of broilers.

BCAA

Additional branched-chain amino acids, such as isoleucine and valine, help reduce crude protein in the diet.

The three BCAAs (leucine, isoleucine, and valine) belong to the category of essential or indispensable amino acids.

Unlike other BCAAs, valine is a limiting amino acid in corn-soybean diets, it is more susceptible to antagonism and enzymatic degradation than isoleucine, in response to the addition of leucine in the diet. Therefore, valine should often be added to diets with low protein content.

The three BCAAs are structurally similar and are initially cleaved by branched-chain amino transferase (BCAT) and then by the branched-chain alpha-keto acid dehydrogenase (BCKD) complex, leading to irreversible catabolism to coenzyme A compounds. Stimulation of this enzymatic activity by one of the BCAAs, usually leucine, leads to the catabolism of other BCAAs, and thus an excess level of certain BCAAs may lead to the degradation and deficit of other BCAAs present in lower concentrations.

Several studies have shown that excessive levels of leucine and, to a lesser extent, isoleucine, impair the growth of chicks and the utilization of other BCAAs, while excess valine does not significantly affect the utilization of leucine or isoleucine.

Feed ingredients included in poultry diets contain disproportionate levels of leucine compared to other BCAAs, which can cause a BCAA imbalance. To avoid this, it is recommended to timely introduce complex amino acid mixtures or Vitamix premixes into the poultry diet.

When diets with low protein content are formulated by reducing protein sources and increasing grains with high leucine content, there is an increased likelihood of antagonistic action of leucine on other BCAAs. A high level of leucine with imbalanced other amino acids can enhance amino acid degradation and disrupt muscle growth in poultry.

Formulations with high protein content may be more effective in the early growth phase of poultry as they provide a higher concentration of limiting amino acids. This can prevent problems associated with the deficit of assimilated amino acids. However, a high level of protein may not ensure the proper utilization of BCAAs, which are supplied in low concentrations, or other amino acids present in excess.

There are claims that BCAA imbalance in the diet negatively affects the productivity of broilers. However, a high level of leucine may not provoke harmful effects of antagonism on other BCAAs if an adequate level of protein is achieved by meeting the minimum requirements for isoleucine and valine.

Valine and Isoleucine

For optimal utilization, the correct ratio of BCAAs is necessary in the diet to achieve the proper balance of BCAAs. Otherwise, BCAAs exceeding the maximum concentration of assimilated amino acids will be used for energy rather than protein synthesis.

Experiments have shown an increase in body weight in poultry and total protein and albumin in blood plasma in response to the addition of only L-valine. Further improvement of these parameters was recorded for the addition of both L-valine and L-isoleucine. It has been established that a valine-deficient diet can lead to deterioration of growth performance and the development of feather and leg problems in chickens.

Before further improving the diet by adding isoleucine, the valine needs of the poultry organism must be satisfied. Thus, valine can be considered as the fourth limiting amino acid in chicks raised on corn-based diets.

Leucine

It is known that leucine stimulates protein synthesis, but additional leucine can also reduce the concentration of isoleucine and valine in blood plasma, so the optimal amount of leucine in the diet should be determined based on the types of ingredients used in feeds.

A study was conducted where adding 0.5% leucine to the diet of broilers led to a 9% increase in carcass weight. Birds were fed experimental diets from 3 to 6 weeks of age.

In studies that used a nonlinear regression model to determine the ideal lysine:leucine:isoleucine:valine ratio in broilers for 10-20 days and 25-35 days, it was concluded that the requirement for leucine and valine is higher during the late growth phase of birds. Therefore, researchers increased the optimal amino acid ratio from 100:94:55:65 at the starting phase to 100:106:56:72 at the finishing phase. Current scientific literature writes that lower concentrations of BCAA are necessary for optimal growth of adult birds. However, the BCAA to lysine ratio increases in the late stages of fattening.

Effect of BCAA on bird immunity

In the liver, among BCAA, valine primarily stimulates lymphogenesis of granular and agranular lymphocytes and also increases the number of natural killer cells (NK). BCAA also serve as a stimulator of secretory immunoglobulin A of the mucous membrane, which reduces pathogenic proliferation.

BCAA play an important role as a “source of fuel” for leukocytes, pro-inflammatory cytokines such as IL-12, and dendritic cells. They function to enhance both innate and adaptive immune responses. Studies show that BCAA have both anabolic and immunomodulatory effects.

The level of cortisol in serum in the studied groups of birds receiving BCAA + arginine + cysteine decreased from 3.5 μg/dl to 1.7 μg/dl on day 10, while haptoglobin decreased from 19.84 mg/dl to 13.59 mg/dl, and insulin-like growth factor-1 increased from 144 μg/l to 231 μg/l on day 35 compared to the control group.

In general, the optimal amount of amino acids is important for the synthesis of cytotoxic molecules, polypeptides, immunoglobulins, cytokines, etc., as well as for the chemical bonding and functioning of both the innate and adaptive immune systems. Therefore, it is important to timely provide a balanced complex in feeding and use Vitamix premixes for broilers.

Impact of BCAA in intestanal development and nutrient transport

It is very important for birds to have sufficiently long villi in the intestines, which creates a larger surface area and allows better absorption of nutrients. Through interaction with food and intestinal microbes, as well as through aging, regular shedding of epithelial cells of the villi occurs, which can be significant during certain diseases. Lost villus cells are replenished from crypts, which actively divide. During villus atrophy, crypt depth increases, so the villus/crypt ratio is a good indicator of intestinal health.

Adding leucine may not always be accompanied by growth and proliferation of intestinal cells if the leucine to isoleucine and valine ratio is unbalanced. BCAA metabolism provides carbon skeleton and nitrogen for other amino acids, especially glutamine, thereby supporting immune activity. Increased intake of BCAA in bird brain limits high glutamate accrual and prevents reaching toxic levels of this neurotransmitter. Additionally, alanine and glutamine formed by BCAA transamination prevent accumulation of ammonia in muscles and transport it to the liver and kidneys for further metabolism and excretion.

Essentially, amino acids are the building blocks of peptides produced endogenously and can have antimicrobial action. The epithelial cell membrane of the intestine produces broad-spectrum antimicrobial peptides, including defensins and cathelicidins, to prevent continuous microbial invasion.

Conclusions

BCAA are one of the main regulators of protein synthesis. Accumulated data underline the important role of BCAA in maintaining immune response in domestic birds.

The link between BCAA ratio and breast muscle myopathies is insufficiently studied and requires further research. The role of BCAA in forming the integrity of the intestine and its microbiome has been studied, but the requirements for BCAA have not been standardized on this basis. When formulating diets for birds, ingredients should be carefully selected to provide the correct ratio of BCAA. Corn and soybean meal have higher leucine content compared to other BCAA, while soybean meal and meat and bone meal have a more balanced BCAA ratio.

Moreover, the level of amino acid digestibility should be taken into account when calculating their ratio, as additional free amino acids may not be utilized in the diet the same way as protein-bound amino acids. Further research is needed to understand the impact of the range of BCAA ratios in bird feeding, which would optimize the levels of addition of main feed ingredients with varying BCAA contents.

BCAA have a physiological impact on bird productivity and health. Observations and interpretations of this review can guide future research to adjust recommended BCAA levels in feeding programs in the absence of subtherapeutic antibiotics in birds.

The Vitamix premix range from Vitagro Nutrition ensures the optimal balance of vitamins and minerals for birds, promoting their health and effective feeding.