The effects of probiotics on the performance, egg quality and blood parameters of laying hens: A meta-analysis

A meta-analysis was conducted to determine the effects of probiotics on the performance, egg quality and blood parameters in laying hens. A database was designed based on published papers reporting the use of probiotics in laying hens. Articles were rigorously selected according to the Systematic Review Centre for Laboratory Animal Experimentation (SYRCLE) protocols. The final database consisted of 47 in vivo studies with 190 treatment units. The statistical meta-analysis was performed according to the linear mixed models by using R software version 3.6.3. It was shown that dietary addition of probiotics linearly increased (P < 0.001) egg production and concomitantly decreased (P < 0.01) feed egg ratio (FER) with a linear pattern. Egg mass and feed intake were not associated with the probiotic treatment. Concerning egg quality parameters, probiotics did not affect egg weight but increased eggshell thickness (P < 0.001), eggshell weight (P < 0.01) and yolk colour (P < 0.01). Probiotics reduced (P < 0.05) cholesterol and low-density lipoprotein cholesterol while elevated (P < 0.05) high-density lipoprotein cholesterol blood concentrations. In conclusion, poultry products with health-promoting properties can be obtained with the use of probiotics which positively affect production performance, egg quality and blood metabolites parameters in lying hens.