Substituting ethoxyquin with tea polyphenols and propyl gallate enhanced feed oxidative stability, broiler hepatic antioxidant capacity and gut health

The safety of ethoxyquin has garnered increasing attention. This study evaluated the effects of partially substituting ethoxyquin with tea polyphenols and propyl gallate on feed oxidative stability, hepatic antioxidant properties, intestinal morphology and barrier functions, as well as the antioxidant and anti-inflammatory profiles of the intestinal mucosa in broilers. A total of 351 one-day-old male Arbor Acres Plus broilers were randomly assigned to 3 groups, each comprising 9 replicates with 13 birds per replicate. The treatments included a control group (CON) fed a basal diet, an ethoxyquin group (EQ) that received the basal diet supplemented with 120 g/t of ethoxyquin, and a substitution group (TP) receiving the basal diet supplemented with 6 g/t of tea polyphenols, 6 g/t of propyl gallate, and 30 g/t of ethoxyquin. In vitro experiments showed that both EQ and TP supplementation significantly reduced the acid value (AV), peroxide value (POV), and total oxidation value (TOV) of the feeds, with the TP group exhibiting lower AV and TOV than the EQ group. In vivo assessments revealed no significant differences in growth performance among the groups. Additionally, the TP group exhibited significantly higher glutathione peroxidase activity, increased glutathione content, and elevated protein expression of Keap1, Nrf2, and NQO1 in the liver compared to the control group (P < 0.05). Moreover, dietary TP significantly increased liver catalase activity, glutathione content, and NQO1 protein levels compared to the EQ group (P < 0.05). Both additives effectively reduced malondialdehyde levels in the intestinal mucosa by approximately 50% (P < 0.05) through the activation of the Nrf2/ARE pathway, as indicated by increased mRNA expression of TXN, CAT, GPX1, and GPX4 (P < 0.05). Furthermore, compared to the control group, the TP group exhibited greater villus height and villus height-to-crypt depth ratio (VCR) in the jejunum, as well as elevated VCR in the ileum (P < 0.05). The TP group also achieved the lowest serum levels of diamine oxidase activity, D-lactate and lipopolysaccharide contents among all groups (P < 0.05). The inclusion of both EQ and TP increased the mRNA expression of Occludin, Claudin-1, Mucin-2, and E-cadherin in the jejunum (P < 0.05). Moreover, the combination of tea polyphenols and propyl gallate effectively mitigated the proinflammatory effect of ethoxyquin, as evidenced by reductions in TNF-α, IL-18, and IFN-γ expression, potentially mediated by inhibition of the TLR-4/MyD88/NF-κB signaling pathway. In conclusion, this study demonstrates that partially replacing ethoxyquin with tea polyphenols and propyl gallate enhances feed oxidative stability, liver antioxidant capacity, and gut health in broilers, suggesting an efficient alternative with a lower dosage requirement.