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.

Coccidiosis is a major parasitic disease that suppresses poultry productivity and causes significant global economic losses. Currently, controlling Eimeria parasites relies primarily on the use of anticoccidial drugs or live vaccines. However, these conventional control strategies face the dual constraints of escalating drug resistance and unsustainable economic expenditures. In this study, the efficacy of a chimeric subunit vaccine comprising Eimeria maxima Elongation Factor-1α (EmEF1α) and chicken chemokine Ligand-1 (ChXCL1) was assessed for protection against experimental Eimeria maxima infection. The synthetic gene fragment ChXCL1-EmEF1α was ligated to the pET28a vector and expressed in vitro. Western blot analysis confirmed the successful expression of the recombinant ChXCL1-EmEF1α protein. Chickens immunized with the ChXCL1-EmEF1α exhibited a significantly stronger IgY response and higher secretion of IL-2 and IL-17 compared to those vaccinated with recombinant ChXCL1 alone or challenged solely with E. maxima. Furthermore, the ChXCL1-EmEF1α group demonstrated enhanced anticoccidial effects, including reduced intestinal lesions, higher body weight gain, and lower oocyst shedding compared to control groups. Following E. maxima challenge, the EmEF1α and ChXCL1-EmEF1α groups demonstrated robust protective efficacy, achieving high ACI values of 182 and 178, respectively. In contrast, the ChXCL1 and UC groups exhibited significantly lower ACI values (150 and 149, respectively), indicating minimal protection. This improvement was also reflected in the immune response, with significantly elevated levels of CD4⁺ and CD8⁺ T cells in the ChXCL1-EmEF1α-treated chickens. Moreover, ChXCL1 acts as an effective adjuvant when fused with EmEF1α, enhancing the vaccine’s anticoccidial efficacy. These results suggest that the ChXCL1-EmEF1α chimeric immunogen is a promising candidate for developing subunit vaccines against E. maxima infections.