Precursor of Niacin

Correct Answer: Tryptophan

Tryptophan is the metabolic precursor of Niacin (Vitamin B₃). In poultry and mammals, 60 mg of Tryptophan is required to synthesize 1 mg of Niacin. This conversion is, however, very inefficient.

Why This Matters in Poultry Nutrition

• Poultry do not synthesize Niacin adequately from Tryptophan at practical dietary levels, so Niacin must be supplemented in the feed.
• Interestingly, poultry do not require Niacin supplementation from gut bacteria (unlike ruminants), because poultry gut microbiome is limited.
• Poultry do not require Vitamin C in the feed (can synthesize it), unlike guinea pigs and primates.

Key Vitamin Precursor Relationships

• Tryptophan → Niacin (Vit. B₃) ✔
• β-Carotene → Vitamin A
• 7-Dehydrocholesterol → Vitamin D₃ (by UV light)

Why Other Options Are Wrong

• Tyrosine → precursor of thyroid hormones, melanin, and catecholamines; not Niacin.
• Phenylalanine → precursor of Tyrosine; not directly linked to Niacin.
• Methionine → sulphur-containing amino acid; no direct link to Niacin synthesis.