Amino Acid Imbalance in Different Livestock species, it’s Causes, Mechanism and Biochemical and Nutritional Aspects

Pashu Sandesh, 05 May 2025

Dr. Aakanksh¹, Dr. Monika Karnani², Dr. Manju³

Department of Animal Nutrition

Post Graduate Institute of Veterinary Education and Research [PGIVER] RAJUVAS

              ¹MVSc Scholar, Department of Animal Nutrition, PGIVER RAJUVAS

              ^2,3Assistant Professor, Department of Animal Nutrition, PGIVER RAJUVAS                                                                                                                       

Abstract

Amino acid imbalance occurs when a second limiting amino acid or mixture of amino acid deficient a particular limiting amino acid supplemented in diets, in one or more essential amino acid. Protein level of diet, amino acid antagonism and the extent of difference in total nitrogen content between basal and imbalance diet also induce amino acid imbalance. There is clear evidence that a reduction in the concentration of limiting amino acid in the anterior prepyriform cortex – a region of the brain involved in nutrient sensing – is linked to behavioural changes in animals, particularly a noticeable decrease in feed intake. This effect may be attributed to competition between the limiting amino acid and other amino acid in the imbalanced mixture for transport across the blood brain barrier, which reduces the availability of the limiting amino acid within the brain. Due to amino acid imbalance decrease the concentration of the limiting amino acid in the blood, depression in the feed intake and weight gain, metabolic stress and neurological symptoms also occurs. This imbalance is corrected by increasing dietary content of limiting amino acid and balanced protein intake.

Key words: Amino acid imbalance, feed intake, growth rate, Limiting amino acid, metabolic balance, protein synthesis.

Introduction:

Amino acid plays a vital role in body, as they serve as the building blocks of proteins and are essential for various physiological functions including tissue repair, enzyme production and immune function. Amino acid imbalance in animal diet occurs when the proportions of essential amino acid deviate from the animals biological requirements. When a second limiting amino acid or mixture of amino acid deficient a particular limiting amino acid is supplemented in diets marginal in one or more essential amino acid, it cause amino acid imbalance. Even the other amino acids are abundant, the lack of just one essential amino acid can limit protein synthesis and cause the other to be wasted. Due to amino acid imbalance decrease the concentration of limiting amino acid in blood, depression in feed intake and weight gain, metabolic stress and neurological symptoms also occurs. This imbalance is correct by increased dietary content of limiting amino acid and balanced protein intake.

What is limiting amino acid and limiting amino acid in different species -

A limiting is the essential amino acid (EAA) present in the smallest amount relative to animals requirement. This amino acid limits the body’s ability to synthesize protein even when all other amino acids are present in sufficient quantities.

Causes of amino acid imbalance in animals: -

1. Limiting amino acid in diet – A limiting amino acid is the essential amino acid present in the lowest proportion relative to the animal needs. Even when all other amino acids are available in adequate amounts, the deficiency of just one can limit protein synthesis.
2. Improper feed formulation – Diet based on plant protein often lack certain essential amino acids. For instance, corn is low in lysine, while soyabean meal may be deficient in methionine for poultry. Without precise formulation and supplementation, such diet can result in imbalance.
3. Amino acid antagonism and competition – Some amino acids complete for the same transport systems in the gut or share similar metabolic pathways. An excess of one can suppress the absorption or function of another, exacerbating the imbalance. For example, high level of leucine can interfere with valine and isoleucine utilisation.
4. Low digestibility and bioavailability – Even when amino acids are present in sufficient quantities, they may be not be absorbed effectively due to poor digestibility or the presence of anti – nutritional factors. This leads to a functional deficiency.

Mechanisms of amino acid imbalance: -

1. Incomplete protein synthesis – Protein synthesis in animals requires all essential amino acids in the right proportion. A deficiency in even one EAA results in incomplete protein chains, leading to poor growth, reduced feed efficiency and impaired body functions.
2. Catabolism of surplus amino acids – Amino acids that cannot be used for protein synthesis are deaminated. The nitrogen is excreted as urea or uric acid. While the carbon skeleton is used for energy or stored as fat. This process not only wastes nutrients but also increase metabolic load on the liver and kidneys.
3. Disruption of metabolic balance – An imbalance affects the rations among amino acids, disrupting enzymatic activities, hormone synthesis and immune responses. It can also lead to oxidative stress and altered nutrient metabolism.

Effect on brain function: -

1. Transport across the Blood Brain Barrier – Amino acids are transported into the brain via specific carriers, particularly the large neutral amino acid transporter. When one amino acid is deficient, others may dominant transport reducing the entry of critical precursors for neurotransmitters. For example – excessive leucine can limit tryptophan uptake lowering serotonin production.
2. Neurotransmitters synthesis impairment – Essential amino acids serve as precursors for neurotransmitters.

- Tryptophan for serotonin

- Tyrosine and phenylalanine for dopamine and norepinephrine

A deficiency in these amino acids reduces neurotransmitters synthesis, affecting mood, behaviour and appetite.

3. Appetite regulations and feeding behaviour – The brain detects amino acid deficiency and initiates a feedback mechanism through the hypothalamus to reduce feed intake. This response, observed in poultry and other species, serves as a protective mechanism against further imbalance.

Biochemical and nutritional aspects of amino acids imbalance in different animals: -

Amino acid imbalance arises when essential amino acids are either or present in inadequate proportions in an animal’s diet. This condition distrupts protein synthesis, elevates nitrogen excretion and reduces the overall metabolic efficiency. The impact of such imbalances varies across species, affecting both biochemical functions and nutritional outcomes.

Poultry: -

Biochemical considerations – Methionine deficiency hampers methylation reactions, limiting the synthesis of critical compounds such as creatine and glutathione. This leads to compromised growth performance and weakened immune responses.

Nutritional considerations – Diets with high energy content but imbalanced amino acid profiles result in inefficient feed utilisation and elevated fat deposition. Ensuring appropriate methionine and lysine supplementation is essential to maintain optimal growth and feed efficiency.

Ruminants: -

Biochemical considerations – Methionine and lysine are limiting amino acids for hepatic and mammary protein synthesis. This deficiency may reduce milk yield and elevate blood ammonia concentrations.

Nutritional considerations – Microbial protein synthesis in the rumen may not fully meet the amino acid requirements of high producing animals. Incorporation of rumen protected amino acid into the diet is therefore necessary.

Horse: -

Biochemical considerations – Lysine is vital for collagen formation and muscle protein synthesis. Inadequate lysine level leads  to reduced plasma amino acid concentration and may affect tissue repair.

Nutritional considerations – Forage based diets are generally deficient in lysine. Nutritional strategies should include soyabean meal or synthetic lysine to ensure amino acid adequacy.

Dogs: -

Biochemical considerations – Lysine plays a key role in the production of enzymes and structural protein. A deficiency can elevate blood ammonia due to impaired protein metabolism.

Nutritional considerations – Homemade or grain based commercial dog foods must be evaluated to ensure adequate lysine content to support growth and immune function.

Cats: -

Biochemical considerations – Taurine is essential for bile acid conjugation, retinal health and proper cardiac function. Its deficiency can lead to serious physiological consequences.

Nutritional considerations – As taurine is absent in plant-based proteins, diets for cats must include animal derived protein or be supplemented with synthetic taurine, particularly in commercial formulations.

Swine: -

Biochemical considerations – Lysine deficiency impairs muscle protein synthesis, leading to suboptimal lean tissue growth. Excess amino acid are deaminated, increasing urea production and contributing to energy loss.

Nutritional considerations – Grain heavy pig diets often lack lysine. Supplementing lysine helps enhance growth efficiency and improves nitrogen utilisation in the body

Management of amino acid imbalance: -

Amino acid imbalance can negatively impact animal health and feed efficiency. To minimize these effects and ensure optimal performance it is important to apply proper dietary management strategies that promote a balanced amino acid profile in the feed.

1. Formulating diets based on nutritional requirements – Ration should be designed according to the specific amino acid needs of animal species, age and production state. Using updated nutrient requirement standards helps ensure each essential amino acid is supplied in the correct proportion.
2. Application of the ideal protein concept – The ideal protein concept involves providing amino acids in the same ratio as required by the animal, typically using lysine as the reference point. This method helps reduce excess and deficiencies, promoting efficient utilisation of protein.
3. Use of crystalline amino acids – Supplementing feeds with synthetic amino acids such as lysine, methionine, threonine and tryptophan allow precise adjustment of the amino acid profile. This is especially useful when using plant based protein sources that may lack one or more essential amino acids.
4. Combining Ingredients with complementary profiles - Blending feed ingredients with different amino acid contents can help balance the overall profile. For example, cereals low in lysine can be combined with protein meals rich in lysine to improve overall nutritional quality.
5. Regular feed analysis and monitoring – Routine evaluation of feed composition and animal performance helps identify potential imbalances early. Adjustments can then be made to maintain nutritional adequacy and support optimal productivity.

Conclusion: -

Amino acid imbalance, particularly due to the presence of a limiting amino acid, can significantly affect protein synthesis, feed efficiency, growth and even brain function in animals. The imbalance often results from improper feed formulation, low digestibility or disproportionate amino acid levels, leading to metabolic stress and behavioral changes such as reduced feed intake. Proper nutritional management is essential to prevent and correct these imbalances. Applying the ideal protein concept, Supplementing with digestible crystalline amino acid and carefully selecting and combining feed ingredients are key strategies. In addition regular monitoring and adjustment of ration based on the animals physiological needs can ensure optimal amino acid supply. By focusing on amino acid balance rather than simply total protein content production can improve animal health, enhance productivity and reduce nitrogen waste ultimately supporting more efficient and sustainable livestock production.

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