This experiment investigated the effects of seaweed polysaccharide (SP) and seaweed enzymatic hydrolysate (SEH) on the growth performance, serum biochemical indices, antioxidant capacity, and intestinal function of Muscovy ducks. A total of 240 healthy 1 day female Muscovy ducks (48.85 ± 0.45 g) were randomly divided into 3 treatment groups, with 4 replicates per group and 20 ducks per replicate. The control (CON) group received a basic diet supplemented with 20 mL/kg of water, the SP group received a basic diet supplemented with 20 mL/kg of SP, and the SEH group received a basic diet supplemented with 20 mL/kg of SEH. The experimental period lasted for 28 d. The results indicate that, compared to the CON group, the average daily feed intake (ADFI) and feed to gain (F/G) of the SP and SEH groups of ducks significantly decreased at 28 d (p < 0.05). In the SP group, serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST), as well as the concentrations of glucose (GLU), triglycerides (TG), total cholesterol (TCHO), low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C), were significantly reduced (p < 0.05). In the SEH group, the activities of ALT and AST were also significantly lower (p < 0.05). Additionally, serum total antioxidant capacity (T-AOC) levels and superoxide dismutase (SOD) activity in the SEH group were significantly higher than those in the CON group (p < 0.05), while the malondialdehyde (MDA) content was significantly reduced (p < 0.05). Compared to the CON group, serum levels of immunoglobulin A (IgA), immunoglobulin G (IgG), interleukin-4 (IL-4), and interleukin-10 (IL-10) in the SP group were significantly increased (p < 0.05), whereas the levels of tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), and interleukin-6 (IL-6) were significantly decreased (p < 0.05). In the SP and SEH groups, the villus height (VH) and the villus height to crypt depth (V/C) of the Muscovy ducks significantly increased (p < 0.05), while the crypt depth (CD) significantly decreased (p < 0.05). A significant increase in the abundance of Barnesiella was observed in the SP and SEH groups (p < 0.05), whereas the abundances of UCG-005 and Romboutsia significantly decreased (p < 0.05). LEfSe analysis indicated that g__Bacillus and g__Veillonella were significantly abundant in the SP group (p < 0.05), while g__Coriobacteriaceae_UCG_002 was significantly abundant in the SEH group (p < 0.05). In summary, the addition of SP and SEH to the feed can promote the healthy growth of ducks by improving intestinal morphology, regulating the structure of intestinal microbiota, enhancing antioxidant capacity and immune function, and optimizing metabolic indicators. This occurs while reducing feed intake and feed-to-weight ratio, and there is a certain specificity in their mechanisms of action.

Heat stress (HS) causes reproductive damage in female mammals, including pigs, cattle, and sheep. As the primary site of estrogen (E₂) biosynthesis, follicular granulosa cells (GCs) act as the critical target of HS injury. Previous studies have shown that cinnamaldehyde (CA) effectively participates in reproductive regulation in mice. Therefore, female mice and their follicular GCs were taken as the research subjects in this study. First, we adopted ELISA and H&E staining to investigate the effects of CA on ovarian follicular histology and E₂ secretion in mice. Second, CCK-8 assay, flow cytometry, and ELISA were applied to clarify how CA regulates proliferation, apoptosis, and E₂ secretion of mouse follicular GCs under HS. Finally, RT-qPCR and Western blotting (WB) were used to elucidate the protective effects of CA together with its underlying molecular mechanisms. Animal experiment results revealed that HS elevated the proportion of primordial and primary follicles and suppressed E₂ secretion. Oral gavage of mice with CA at 25 mg/kg exhibited no obvious hepatotoxicity. This dosage effectively increased the percentage of secondary and antral follicles, alleviated HS-induced histological damage in ovaries, and raised serum E₂ levels both under normal conditions and HS. Further in vitro cell experiments confirmed that HS reduced cell viability and accelerated apoptosis in mouse follicular GCs. HS decreased estrogen secretion by downregulating the relative protein expression of StAR and CYP19A1. Treatment with CA at a concentration of 2.5 × 10⁻⁵ M significantly increased cell viability and inhibited excessive apoptosis in mouse follicular GCs under HS. Under HS conditions, CA treatment elevated E₂ secretion in mouse follicular GCs by upregulating the relative protein expression of StAR and CYP19A1. In conclusion, the findings of this study indicate that CA holds promise as a natural anti-HS additive.