Fucoidan alleviates spleen damage in heat-stressed broilers by suppressing oxidative stress, ferroptosis and...

Heat stress (HS) causes organ damage and has detrimental impacts on the welfare and production in broilers. As a crucial immune organ, the spleen exerts a key role in immune homeostasis of broilers. Fucoidan (FUC) is a marine functional substance and extracted from seaweeds with multiple biological activities, such as anti-inflammatory and antioxidant effects. This experiment attempted to investigate the protective effect of fucoidan on HS-induced spleen injury in broilers. A total of 240 male Arbor Acres (AA) broilers at 21 d of age were randomly assigned to five groups: control (CON) group, HS group, and HS group supplemented with 200 (HS+FUC₂₀₀), 400 (HS+FUC₄₀₀) and 800 (HS+FUC₈₀₀) mg/kg FUC. The feeding trial lasted 21 d. The results showed that HS reduced the spleen index, impaired antioxidant capacity, and induced pathological damage in the spleens of broilers. Dietary supplementation with 200, 400, and 800 mg/kg FUC alleviated these injuries. Specifically, 800 mg/kg FUC improved the spleen index, antioxidant indicators and the splenic histomorphological pathology in broilers under HS. Therefore, 800 mg/kg of FUC was identified as the effective dosage for mitigating HS-induced splenic injury in broilers. Accordingly, this study further investigated the molecular mechanism of the beneficial effects of 800 mg/kg FUC. FUC₈₀₀ upregulated the expression of antioxidant genes (NQO1, CAT, SOD1, SOD2, GCLC, GCLM, GSTA3, HO-1) and ferroptosis-related genes (GPX4, SLC7A11, Fpn1, FTH1), while downregulating the expression of inflammatory genes (IL-1β, IL-4, TNF-α, NF-κB) in the spleen of heat-stressed broilers. Besides, FUC₈₀₀ reduced the protein expression of total P65 and p-P65, and enhanced the protein expression of total Nrf2 and p-Nrf2 in the spleen of heat-stressed broilers. The findings demonstrated that dietary supplementation of 800 mg/kg FUC alleviates HS-induced spleen damage in broilers by reducing the oxidative stress, ferroptosis and inflammation, and the protective role of FUC is related to the activation of Nrf2 signaling and the suppression of NF-κB signaling. This study offers theoretical support for applying FUC in improving the spleen health of broilers under HS conditions.