This experiment was conducted to determine the effect of using L-threonine and reducing dietary levels of crude protein (CP) on egg production criteria in layers. Three hundred of Hy-Line W36 laying hens were used in this experiment. This experiment consisted of three experimental treatments with five replications in each. Experimental treatments included 3 diets with different levels of CP which were 15, 16 and 17% with 0.1, 0.05 and 0.02% L-threonine supplementation, respectively. Experimental period lasted for 5 weeks. In this experiment quantitative factors such as egg mass, egg weight, egg production percentage, feed conversion ratio (FCR), body weight and feed intake were measured. Measured data were analyzed by completely randomized design (CRD). Results indicated that reducing dietary levels of CP to 15% and using L-threonine supplementation had no significant effect (P>0.05) on laying criteria. According to economic analysis, the treatment containing 15% CP and 0.1% L-threonine was the most beneficial treatment. پرونده مقاله