L-Leucine Administration Causes Growth Retardation and Modifies Specific Amino Acid Metabolism in Broiler Embryos.

L-Leucine (L-Leu) administration was demonstrated to afford thermotolerance and modified amino acids metabolism in post-hatched broiler chicks under heat stress. This study aimed to investigate the changes in embryonic growth and amino acid metabolism after injection of L-Leu. Fertilized broiler eggs were subjected to injection of sterile water or L-Leu on embryonic day (ED) 7. The weight of embryos and yolk sacs were measured on ED 12, 14, 16, and 18. Plasma and livers were collected on ED 14 and 18 for free amino acid analysis. The weight and relative weight of embryos were significantly lowered by administration of L-Leu, but those of yolk sacs were not altered. Moreover, L-Leu injection significantly reduced the plasma proline concentration during embryogenesis and increased the plasma concentrations of tyrosine (Tyr) and lysine (Lys) in ED 18. Hepatic Lys concentration was also significantly increased by L-Leu injection. Interestingly, Leu concentrations in the plasma and liver were not affected by L-Leu administration. These results indicated that administered L-Leu was metabolized before ED 14 and affected embryonic growth and amino acid metabolism during embryogenesis.