Which amino acid is typically the first limiting in poultry diets?

• A. Methionine.
• B. Leucine.
• C. Lysine.
• D. Tryptophan.

Answer: (C)

In poultry, the first limiting amino acid is the essential one that is shortest relative to the bird’s requirement in the diet, so it ultimately limits protein synthesis and growth. In typical broiler diets based on corn and soybean meal, lysine is the most limiting because corn is relatively deficient in lysine while other essential amino acids are better supplied by the soybean meal. When lysine is lacking, no amount of other amino acids can fully support growth, making lysine the key bottleneck to performance. That’s why lysine is used as the reference point for balancing diets; once its level is set to meet growth needs, other amino acids are adjusted relative to it. Methionine is often the next limiting one in these diets, while leucine and tryptophan can become limiting if lysine is already adequate but others aren’t, but they don’t typically limit first.