This study investigates the effects of quercetagetin (QG) supplementation on the antioxidant capacity, liver mitochondrial function, and cecal microbiota of broilers raised under high-density conditions. A 2 × 2 factorial design with 144 one-day-old WOD168 broilers, which were allocated to two stocking densities (LD: 4 birds per cage, equivalent to 11.1 birds per square meter; HD: eight birds per cage, equivalent to 22.2 birds per square meter) and two levels of dietary supplementation of QG (0 and 20 mg/kg). At the conclusion of day 21, broilers of similar body weights were randomly allocated into four groups (22 to 42 d): control (CON), QG treatment (QG), high stocking density (HSD), and high stocking density with QG supplementation (H_QG). The results demonstrated that HD groups significantly reduced broiler growth performance, including body weight (BW), average daily gain (ADG), and average daily feed intake (ADFI) (p < 0.05). Additionally, HD groups increased serum stress hormone levels (CORT and ACTH), pro-inflammatory cytokines (IL-1β and IL-6) (p < 0.05), while decreasing liver antioxidant enzyme activities (GSH-Px, T-SOD), serum CAT and T-SOD activities, and mitochondrial function (GSH, complex I-III, ATP contents) (p < 0.05). However, dietary supplementation with 20 mg/kg QG significantly alleviated the negative effects induced by HSD, restoring growth performance, stress hormone levels, immune parameters, and liver antioxidant and mitochondrial function. Moreover, QG supplementation markedly improved cecal microbiota composition, enhancing gut health. Correlation analysis revealed a strong association between microbial composition and overall broiler health, indicating that gut microbiota plays a critical role in mediating these beneficial effects. In conclusion, QG exhibits protective effects against oxidative stress, mitochondrial dysfunction, and gut microbiota imbalance induced by high-density rearing, suggesting its potential as a functional feed additive to improve broiler health under intensive farming conditions.

Oxidative stress is a major constraint on broiler health and productivity. Mitochondrial dysfunction and gut–liver axis disruption play pivotal roles in this process. The present study investigated whether dietary quercetagetin (QG) alleviated diquat (DQ)-induced oxidative stress in broiler chickens through modulation of PINK1/Parkin-mediated mitophagy and gut–liver axis homeostasis. A total of 144 1-day-old WOD168 broilers were randomly assigned to four treatments with six replicate cages of six birds per cage: control group (non-challenged, basal diet), DQ group (DQ-challenged, basal diet), D_QG group (DQ-challenged, basal diet with 20 mg/kg QG), and QG group (non-challenged, basal diet with 20 mg/kg QG). On day 35, the DQ and D_QG groups were intraperitoneally administered DQ (20 mg/kg body weight). Dietary QG significantly increased body weight and attenuated the loss in average daily gain induced by DQ, while reducing serum aspartate aminotransferase levels. DQ challenge impaired gut barrier function, as indicated by decreased villus height, villus height/crypt depth ratio, and mRNA expression of Claudin-1 and ZO-1 (P < 0.05), exacerbated hepatic lesions, and significantly altered cecal microbial diversity. QG supplementation significantly attenuated the drop in glutathione peroxidase activity and downregulated PINK1 and LC3-II in hepatic mitochondria. It also significantly increased complex I activity, mitochondrial DNA copy number, and adenosine triphosphate content, while decreasing DQ-induced reactive oxygen species. Collectively, these results indicate that dietary QG alleviates DQ-induced oxidative stress by preserving mitochondrial function, potentially modulating PINK1/Parkin-related mitophagy, enhancing intestinal barrier integrity, and modulating cecal microbial composition.