Abstract
This experiment was performed to investigate the effects of leucine (Leu) supplementation on performance, egg quality, egg cholesterol content, antibody titer, and serum biochemistry in laying hens. A total of three hundred commercial laying hens (33 to 41 wk, LSL strain) were used in a completely randomized design with six treatments and five replicates of 10 birds each. The six dietary treatments consisted of graded levels of L-Leu supplementation (0, 0.1, 0.2, 0.3, 0.4, and 0.5 %) added to a basal diet containing 1.08% digestible leucine. The performance of laying hens (egg production, egg weight, egg mass, feed intake, and feed conversion ratio) was not significantly affected by dietary L-Leu supplementation. Egg quality traits (shape index, relative weights of shell, albumen, yolk, and shell thickness) were significantly (P < 0.05) affected by the Leu levels, with the highest quality observed at 0.1% L-Leu supplementation. Egg cholesterol content was significantly (P < 0.05) lower in the L-Leu supplemented groups compared to the control group. Serum antibody titers against Newcastle disease (ND) and avian influenza (AI) viruses were significantly increased (P < 0.05) by dietary L-Leu supplementation. At higher levels of L-Leu supplementation (0.3 to 0.5%), serum albumin, calcium, and total protein decreased (P < 0.05), while uric acid and triglyceride concentrations increased (P < 0.05). In conclusion, dietary supplementation of L-Leu at the level of 0.1% improves egg quality traits and immunity in laying hens without compromising their performance.