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

Abstract

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<0.01) weight gain and feed efficiency when lysine intake was higher than the requirements, i.e., their effects were more significant when the experimental diets were deficient in lysine. Other methodological limitations are listed, particularly the absence of essential details about the methodology and treatments in the experimental design, and few studies included health challenges. In summary, further studies in this field are needed; however, future trials should test the synergistic effects of phytogenic additives (experimental designs including individual and combined compounds), as well as their dose-response in pig performance.