Surreal illustration of broiler chicks surrounded by glowing amino acids and enzyme structures.

Boost Broiler Health: How Threonine, Lysine, and Glycine Impact Poultry Enzymes

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Samir D’Costa in Health & Wellness August 2025 • 4 min read.

"Unlock the secrets of optimal broiler nutrition with insights into digestible amino acid ratios and their effects on enzymatic activity."


In animal diets, an imbalance of amino acids can trigger a rapid decrease in the limiting amino acid's concentration in the blood. This biochemical response is a critical consideration for poultry farmers aiming to optimize feed efficiency and support healthy growth in broilers.

For poultry, particularly those fed corn and soybean meal-based diets, threonine often emerges as the third limiting amino acid. Beyond its role in protein synthesis, threonine contributes to the formation of other essential metabolites, including glycine. Understanding how to manage threonine levels is vital for supporting overall metabolic health.

This article delves into recent research examining the impact of varying digestible threonine to lysine ratios, with and without glycine supplementation, on the activity of key enzymes involved in threonine metabolism in broiler chicks. We'll explore how these nutritional adjustments can influence enzyme activity and overall broiler health.

Decoding Threonine's Role: Enzyme Activity and Broiler Health

Surreal illustration of broiler chicks surrounded by glowing amino acids and enzyme structures.

The metabolism of threonine involves three key enzymes: threonine dehydratase, threonine dehydrogenase, and threonine aldolase. Each enzyme plays a distinct role in processing threonine, influencing energy production, glucose synthesis, and the availability of glycine for other metabolic processes.

A recent study investigated how different digestible threonine to lysine ratios, with or without glycine supplementation, affect the activity of these enzymes in broiler chicks. Researchers at the Universidade Federal de Viçosa in Brazil, used 560 male Cobb broiler chicks over a 13-day period. The chicks were divided into groups receiving different diets, and enzyme activity was measured in liver samples.

  • Threonine Aldolase: Activity was highest with a 75% threonine to lysine ratio. Glycine supplementation generally reduced activity, suggesting that adding glycine spares threonine from being converted into glycine.
  • Threonine Dehydrogenase: Peak activity occurred at a 65% threonine to lysine ratio. Again, glycine supplementation decreased activity, indicating less need for threonine breakdown when glycine is readily available.
  • Threonine Dehydratase: The 55% threonine to lysine ratio resulted in the highest activity. Glycine supplementation also reduced the activity of this enzyme.
These findings highlight the delicate balance in broiler nutrition. Manipulating threonine to lysine ratios and supplementing with glycine can directly influence how these enzymes function. Ultimately, this impacts the metabolic pathways involved in growth, energy production, and overall health.

Optimizing Broiler Diets: Practical Takeaways

The study underscores the importance of carefully balancing threonine and lysine levels in broiler diets. These findings suggest that a 75% threonine to lysine ratio supports higher threonine aldolase activity. In contrast, lower ratios may increase threonine dehydratase activity. Moreover, glycine supplementation consistently reduces the need for threonine catabolism, potentially freeing up threonine for protein synthesis.

While the research focused on enzyme activity within the liver, remember that these metabolic processes impact the whole bird. Optimizing amino acid ratios and considering glycine supplementation may lead to improved growth rates, feed efficiency, and reduced metabolic stress.

Poultry nutrition is a complex science. As always, consult with a qualified poultry nutritionist to tailor feeding strategies to your specific broiler breed, production goals, and environmental conditions.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

Everything You Need To Know

1

Why is it important to balance amino acids like Threonine and Lysine in a broiler's diet?

An imbalance of amino acids, like Threonine and Lysine, can drastically reduce the concentration of the limiting amino acid in the blood. For broilers, this is significant because it impacts feed efficiency and healthy growth. The implications include potential growth retardation and compromised metabolic function if these amino acid ratios are not properly managed.

2

What is the role of Threonine in broiler nutrition and why is it important?

Threonine is the third limiting amino acid in corn and soybean meal-based diets for poultry. Beyond its role in protein synthesis, it's crucial for creating essential metabolites, including Glycine. Managing Threonine levels is vital for supporting overall metabolic health because it directly impacts the availability of Glycine and influences several metabolic pathways within the bird.

3

What are the key enzymes involved in Threonine metabolism, and what do they do?

Threonine Aldolase, Threonine Dehydrogenase, and Threonine Dehydratase are key enzymes involved in Threonine metabolism. They each perform distinct functions: Threonine Aldolase impacts the formation of Glycine, Threonine Dehydrogenase influences energy production, and Threonine Dehydratase is involved in glucose synthesis. Their activity is directly influenced by the ratios of Threonine to Lysine and Glycine supplementation, affecting various metabolic processes.

4

How do varying Threonine to Lysine ratios and Glycine supplementation affect enzyme activity in broilers?

The study found that a 75% Threonine to Lysine ratio resulted in the highest Threonine Aldolase activity, while lower ratios might increase Threonine Dehydratase activity. Glycine supplementation generally reduced the activity of all three enzymes, suggesting the body utilizes Threonine more efficiently when Glycine is available, potentially supporting protein synthesis and reducing Threonine breakdown.

5

What are the practical implications of these findings for optimizing broiler diets?

Carefully balancing Threonine and Lysine levels and considering Glycine supplementation in broiler diets is important. By understanding the impact on enzyme activity and metabolic pathways, poultry farmers can optimize feed efficiency, promote healthy growth, and potentially improve overall bird health. The correct ratios and supplementation strategies can help to support protein synthesis and other important metabolic functions.

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