Effects of dietary L-leucine supplementation on performance, egg quality, serum biochemical parameters, antibody titer, and egg cholesterol content of laying hens

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.