The effect of diet protein level on productive performance and egg quality of laying hens during the second production period

An experiment was conducted to examine the influence of dietary protein level on productive performance egg quality and some faecal and serum traits of laying hens during the second production period. Accordingly, the aim of this study was to determine optimum protein level for molted hens. A total of 432 Super Nick laying hens, 82 wk of age, were used in the present study. After being molted, laying hens were distributed in a completely randomized experimental design with 3 crude protein levels (18.5, 17.0 and 15.5 %) with 3 treatments and 6 replicates of 24 birds each. The experiment lasted between 86 and 105 wk of age. Diets in mash form were prepared at three different protein levels.Dietary protein level significantly influenced performance indices (P<0.01) and some of the egg quality traits including eggshell weight and thickness, yolk weight and yolk colour (P<0.05) of laying hens. As the dietary protein level was elevated egg production rate, egg weight and egg mass, feed consumption and total egg yield were increased in a similar pattern. Increasing dietary protein level from 15.5 % to 18.5 % elicited an increase in total egg yield and egg mass output by 8.48 % and 4.37 g, respectively; however, when protein was moderately reduced (from 18.5 to 17.0 %) performance traits were slightly diminished. The worst feed conversion ratio was determined in hens fed on a diet with 15.5 % protein with a deterioration of 4.5 % as compared to the treatment with 18.5 %. Hens administered diet with 18.5 % protein produced eggs lower in shell weight and thickness as compared to eggs laid by hens receiving diet either at the level of 17.0 % or 15.5 %. Any of the blood constituents was not affected by dietary protein level except of the IgM concentration (P>0.05). Decreasing dietary protein level significantly reduced faecal excretion of nitrogen and uric acid (P<0.01). In conclusion, provision diet with 18.5 % protein instead 15.5 % improved egg production rate by 6.13 % as well as egg weight by 1.60 % in forced molted hens during the second production period. Data indicated that a diet with 18.5 % protein level instead 15.5 % is recommended for laying hens induced forced molting in order to rapidly restore body mass and maintain the high productive performance during the second production phase.