Hartanto, S.; Wardono, H. P.; Kurnianto, H.; Hantoro, F. R. P.; Prasetyo, A.; Haryanto, B.; Hayati, R. N.; Ludfiani, D. D.; Purwasih, R.; Yano, A. A.; Sujiwo, J.; Jang, A.; Sugiharto, S.

Objective: The study aimed to evaluate impact of quercetin supplementation on performance, egg production, egg quality, blood metabolites, malondialdehyde (MDA) levels and anti-oxidant activity in laying hens. Methods: The meta-analysis study synthesized 27 included studies. We applied mean difference (MD) calculation using restricted maximum likelihood random-effects model to determine the effect size of quercetin treatments. A mixed-effects model was used in subgroup analysis to evaluate the influence of quercetin dose. Results: Quercetin treatments increased (p<0.05) laying rate (LR) (MD = 2.819%), egg weight (EW) (MD = 1.209 g/unit), haugh unit (HU) (MD = 1.838%), shell thickness (ST) (MD = 0.014 mm), and yolk colour (YC) (MD = 0.526). Feed-to-egg ratio (FER) was reduced (MD = -0.146; p<0.05) in quercetin-treated laying hens. Quercetin decreased (p<0.05) serum glutamic pyruvic transaminase (SGPT) (MD = -7.009 U/L), glucose (MD = -17.589 mg/dL), and total cholesterol (MD = -20.834) levels in laying hens. High-density lipoprotein (HDL) concentration was improved (MD = 32.590 mg/dL; p<0.05) by quercetin supplementation. Quercetin dietary reduced (MD = -7.373 nmol/mL; p<0.05) MDA level. Moreover, superoxide dismutase (SOD) concentration (MD = 8.114 U/mL; p<0.05) was enhanced in quercetin-administrated laying hens. Quercetin dose linearly affected (p<0.05) the SGPT, glucose, and total cholesterol levels. However, quercetin dose had quadratic effect (p<0.05) on LR, FER, and SOD content. Conclusion: quercetin treatments effectively improved performance, egg production, egg quality, blood metabolites, and anti-oxidant defence in laying hens. The effective quercetin dose for optimizing LER, FER, and SOD content was 400 to 600 mg/kg.