Dietary Phytogenic Extracts Favorably Influence Productivity, Egg Quality, Blood Constituents, Antioxidant and Immunological Parameters of Laying Hens: A Meta-Analysis

SIMPLE SUMMARY: The application of phytogenic extracts in the poultry diet has been widely evaluated along with the prohibition on antibiotics use as growth promoters. Phytogenic extracts have been proven to improve the digestive health and performance of laying hens due to their antimicrobial, antioxidant, and immunomodulatory properties. However, several studies have also discovered negligible or even negative effects on the productive parameters or egg quality when added to diets at a high level. Through this meta-analysis approach, we found optimal levels of dietary phytogenic extracts that could be considered to avoid negative effects on laying hens. Furthermore, our findings support the suitability of phytogenic extracts for use as natural feed additives to increase the laying hens’ productivity with potential economic benefits. ABSTRACT: 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.