Dietary inclusion of flavonoids and tocopherols for finishing pigs: a systematic review and meta-analysis

Abstract The use of antibiotics as growth promoters in pig farming has been largely restricted, driving the search for alternative natural additives, like phenolic compounds. This systematic review coupled to a meta-analysis aimed to investigate the effects of the inclusion of both flavonoids and tocopherols in the diet of finishing pigs regarding zootechnical performance and meat quality. A search was conducted at the PubMed, Scopus, SciELO, and Web of Science databases up to May 2024, following PRISMA guidelines. A total of 15 articles published between 1999 and 2020 were included, totaling 888 animals. Phenolic compounds were grouped as flavonoids and tocopherols, and variables associated to productive performance, carcass characteristics, and meat quality parameters were assessed. The meta-analysis revealed that flavonoid inclusion results in a quadratic effect on feed conversion, with an estimated optimal point of 502.20 mg/kg. Tocopherol inclusion, in turn, leads to a quadratic trend concerning final body weight, with an estimated optimal point of 139.61 mg/kg. Regarding meat quality, flavonoids decreased the values of the colour parameters a* and b*, while tocopherols positively influenced parameters L* and a* and displayed a propensity to reduce lipid peroxidation (TBARS/MDA). The findings reveal that flavonoid supplementation favors productive performance, while tocopherols are noteworthy for their antioxidant action and pork quality benefits. More well-designed studies, however, are required to determine optimal inclusion levels and elucidate the mechanisms of action of these compounds.