A systematic review and meta-analysis of the effect of phytogenic feed additives on pig performance

•A meta-analysis is a valuable tool for decision-making in pig production.•The effects of phytogenics are highly heterogeneous due to their variable composition.•Oregano and garlic did not improve pig performance.•There is limited information on the evaluated phytogenics in most publications. The present study aimed to evaluate the use of dietary phytogenic additives (DPA) for pigs (nursery, growing, and finishing phases) through a systematic review combined with a meta-analysis. Studies were searched using keywords in English in the PubMed, Scopus, and Web of Science reference search engines. A database containing all relevant information available in the studies was then developed. The selected studies compared the performance parameters of pigs fed control diets with or without antibiotic growth promoters (AGP) with those fed diets containing phytogenic additives. The meta-analysis was carried out following three sequential analyses: graphic, correlation, and variance-covariance. The database included 104 studies. A wide variety of compounds was evaluated in the selected studies, as most of them tested product blends. The most frequently phytogenic additives tested individually were oregano and garlic. However, neither influenced the analyzed performance parameters compared with the control treatments (with or without AGP). Phytogenic additives linearly reduced (P