Abstract: The objective of this study was to investigate the effect of β-mannanase added in SBM based diets on production performance and apparent nutrient availability of laying hens. Six hundred healthy Roman hens (laying hens of 33 weeks old) were selected and randomly divided into 3 groups with two hundred hens in each group. The control group and experiment group 2 and 3 were fed with a same diet added 0%, 0.03% and 0.05% β-mannanase respectively. The study lasted 35 days with the results showing that the egg weight (laying hens of 33 to 37 weeks old) of experiment group 2 and 3 increased 5.12% (P<0.05) and 7.08% (P<0.05) respectively than control group 1; the eggshell thick increased 11.60% (P<0.05) and 9.39% (P<0.05). The egg production rate of experiment group 2 and 3 (laying hens of 51 to 55 weeks old) increased 4.20% (P<0.05) and 5.55% (P<0.05) respectively more than control group 1. The nutrient availability of dry matter, organic matter, crude protein and calcium for experiment group 2 and 3 (laying hens of 36 weeks old) raised 6.15% (P<0.05) and 4.10% (P<0.05), 6.36% (P<0.05) and 6.60% (P<0.05), 2.04% (P<0.05) and 3.21% (P<0.05), 3.84% (P<0.05)and 7.08% (P<0.05) respectively more than control group 1; the egg weight raised 1.32% (P<0.05)and 2.46% (P<0.05). Figures above clearly demonstrate that β-mannanase helps to advance the production performance and apparent nutrient availability of laying hens.

Key words: β-mannanase; laying hens; egg weight; egg production rate; apparent nutrient availability