The present study aimed to assess the impact of dietary phytogenic extracts on laying hen productivity, egg quality, blood constituents, antioxidant, and immunological parameters through a meta-analytical approach. A total of 28 articles (119 data points) reporting the influence of dietary phytogenic extracts on the productive performance, egg quality, blood constituents, immunological, and antioxidant parameters of laying hens were embedded into a database. Statistical analysis was performed using a mixed model, with different studies treated as random effects and phytogenic extract levels treated as fixed effects. This meta-analysis revealed that dietary phytogenic extracts quadratically (p < 0.05) improved egg production and egg mass as well as decreased (p < 0.05) the feed conversion ratio (FCR) with no adverse effect on egg weight and egg quality. Feed intake and egg yolk percentage tended to increase linearly (p < 0.1). Total serum cholesterol and low-density lipoprotein (LDL) declined quadratically (p < 0.001 and p < 0.05, respectively), high-density lipoprotein (HDL) increased linearly (p < 0.001), and malondialdehyde (MDA) decreased linearly (p < 0.01), with increasing levels of dietary phytogenic extract. In addition, immunoglobulin G (IgG), immunoglobulin A (IgA), glutathione peroxidase (GSH-Px), and total superoxide dismutase (TSOD) increased linearly (p < 0.05) in line with the increase in dietary phytogenic extract level. It was concluded that the inclusion of phytogenic extracts in the diet of laying hens had a positive effect on productive performance, feed efficiency, egg mass, immunity, and antioxidant activity without interfering with egg quality. The optimum level of feed photogenic extract for egg production and feed efficiency was determined to be around 300 mg/kg feed.
Keywords: bioactive compounds; egg; laying hens; meta-analysis; polyphenol.