Meta-analysis and systematic review of dietary quercetin effects on broiler performance, carcass traits, and oxidative status

SUMMARYQuercetin is the principal flavonoid compound ubiquitously found in plants and exerts a wide range of pharmacological properties, including antioxidants, antimicrobial, anti-inflammatory, and immunomodulatory effects relevant to livestock health. This systematic review and meta-analysis evaluated the efficacy of quercetin application in broilers’ diets based on production, carcass and meat quality, and antioxidant capacity outcomes. A total of 19 studies were identified, and the data were analysed using a mixed-model meta-analysis to estimate the standardised mean difference (SMD). The results revealed that quercetin exerted significant positive effects on final body weight (BW), feed intake (FI), feed conversion ratio (FCR), and nutrient digestibility under various dietary treatments and stress conditions. Broilers fed low crude protein diets or exposed to ochratoxin showed lower body weight (BW), indicating the negative impact of nutritional deficiency and mycotoxin stress on growth performance. Under these conditions, quercetin supplementation partially alleviated these adverse effects. For instance, quercetin significantly improved BW to the level similar to control diet under oxidative stress challenge. When combined with vitamin E, quercetin yielded the most substantial improvement on final BW, with concurrent effect of improved FCR. Dietary quercetin also improved FI of broilers under oxidative stress. In addition, digestibility of dry matter and crude protein was increased by quercetin administration. Quercetin also exhibited beneficial effects to increase breast muscle percentage and reduce abdominal fat deposition as well as improved meat quality attributes without affecting spleen, gizzard, or bursa size. Quercetin enhanced the oxidative status of broilers by markedly reducing malondialdehyde levels and increasing superoxide dismutase and glutathione peroxidase. These overall results concluded that quercetin administration improves broiler growth, feed efficiency, carcass traits, and antioxidant defence, particularly under stress or nutrient-restricted conditions.