Abstract
Heat stress (HS) is a significant challenge in broilers, which has a negative impact on liver health and metabolic function, endangering broiler production. This study aimed to evaluate the protective effects of dietary fucoidan (FUC) in mitigating HS-induced liver injury and to elucidate the underlying mechanisms. A total of 240 male Arbor Acres (AA) broilers at 21 days of age were randomly divided into five groups: thermoneutral (TN) group, HS group, and HS group supplemented with 200, 400, or 800 mg/kg FUC, respectively. Based on comprehensive assessments of liver histopathology, liver index, and serum biochemical markers-related to liver function (TP, ALB, AST, ALT), 800 mg/kg FUC was identified as the effective dose for alleviating HS-induced hepatic injury, resulting in improvements in liver architecture and function. Further investigations revealed that 800 mg/kg FUC enhanced hepatic antioxidant capacity by increasing T-AOC, T-SOD, and GSH-Px activities in broilers under HS. The non-targeted metabolomics analysis suggested that FUC improves six metabolites in the liver of broilers subjected to HS, including Glu-Asp-Gln, Asn-Pro-Tyr, Glu-Thr-Ile, N-Acetylleucylalanylserine, Octadecyl Fumarate, and Oleoyl-l-Carnitine. The differential metabolites were significantly enriched in several metabolic pathways, such as glycerophospholipid metabolism, fatty acid degradation, and ferroptosis. Furthermore, dietary FUC enhanced the expression of antioxidant genes (GCLC, GCLM, HO-1, SOD2, GPX1, GPX3, CAT1, and GSTA3), suppressed lipogenic genes (SREBP-1, FAS, and ACC), and upregulated the lipolytic gene ATGL as well as the adipogenic regulator PPARγ in the liver of broilers under HS. Additionally, FUC downregulated pro-ferroptotic genes (ACSL4, LPCAT3, and PTGS2) while upregulated anti-ferroptotic genes (Fpn1, FTH1 and SLC7A11) in the liver of heat-stressed broilers. Western blot analysis confirmed that FUC activated the Nrf2 signaling pathway by increasing the protein expression of Nrf2, phosphorylated Nrf2 (p-Nrf2), and nuclear p-Nrf2, while upregulated the AMPK pathway by increasing AMPK and phosphorylated AMPK (p-AMPK) protein levels of the liver in broilers subjected to HS. These findings indicate that dietary supplementation with 800 mg/kg FUC ameliorates HS-induced liver injury through the activation of Nrf2-mediated antioxidant and anti-ferroptosis signaling, and the regulation of AMPK-mediated lipid metabolism balance. This study provides a dietary strategy to improve liver health in heat-stressed broilers, which is beneficial for broiler production during the hot season.