Flavonoids as Dietary Additives in Laying Hens: A Meta-analysis of Production Performance, Egg Quality, Liver, and Antioxidant Enzyme Profile

In this study, a meta-analysis was employed to evaluate the effects of dietary flavonoids on laying hens. A database of flavonoids was developed from published journal papers in which flavonoids were supplemented to laying hens at various doses and then monitored for production performance, egg quality, liver condition, and antioxidant enzyme profile. A total of 22 journal papers were included in the database, and statistically analyzed using a mixed-model methodology in which random effects consisted of the different studies and fixed effects were the dosages of flavonoids. The model statistics were p-value and Akaike information criterion. The significance of an effect was assumed at P < 0.05. The results showed that dietary addition of flavonoids linearly decreased (P < 0.001) feed intake. The laying rate was not affected by the addition of flavonoids, while the FCR tended to linearly decrease (P < 0.1). The addition of flavonoids linearly reduced egg and yolk cholesterol (both at P < 0.001), and linearly increased egg mass (P < 0.001), egg strength (P < 0.05) and yolk color (P < 0.001). Further, a linear decreasing response was observed in the liver triglyceride, and cholesterol concentrations (both at P < 0.001) after flavonoid supplementation. Superoxide dismutase showed a quadratic response (P < 0.01) following the addition of flavonoids. In conclusion, dietary supplementation of flavonoids is able to favourably modulate production performance and egg quality of laying hens.