effect of different levels of crude protein and probiotic (protexin) on performance and blood metabolites of laying hens

this experiment was conducted to evaluate the effects of different levels of crude protein and probiotic in diets on performance, egg quality  and blood biochemical and immunity parameters of laying hens. a completely randomized design with factorial method (2×4) was conducted in which two levels of crude protein (nrc and 10% lower than nrc recommendation) and 4 levels of probiotic (0, .025%, 0.05% and 0.075%) were tested on  288 of hy- line (w36) laying hens for 12 weeks from 42-54 weeks of hens ages. results showed that the different levels of crude protein and probiotic in the diets have significant effects on performance, egg traits and immunity parameters of laying hens (p<0.05). low crude protein diet significantly reduced the egg production percentage, egg mass, feed intake and increased the feed conversion ratio. inclusion of probiotic in the  diets decreased the amount of daily feed intake. using different levels of probiotic with different levels of crude protein could not improve the performance of laying hens. the shell surface weight was decreased when the laying hens received low protein diet. inclusion of probiotic improved the egg specific gravity, but the highest level of probiotic decreased the eggshell percentage. the blood hemoglobin percentage was positively affected by the probiotic content in the diet. different levels of dietary crude protein, probiotic and interaction between them could not significantly changed the blood biochemical parameters