Effects of Single-Cell Protein Derived from Ralstonia eutropha on Growth Performance, Meat Quality, Antioxidant Capacity, and Intestinal Health in Broilers.

This study aims to evaluate the feasibility of substituting soybean meal with single-cell protein derived from Ralstonia eutropha H16 (SCP-H16) in broiler diets, with a specific emphasis on its impact on growth performance, meat quality, biochemical parameters, antioxidant capacity, and intestinal health. A total of 540 one-day-old Arbor Acres (AA) male broiler chicks were randomly allocated to five treatment groups, each comprising six replicates of 18 chicks. The control group (CON) was provided with a corn-soybean meal basal diet, whereas the experimental groups received the basal diet supplemented with 2%, 4%, 6%, and 8% SCP-H16, respectively, replacing soybean meal on an isonitrogenous basis. Specifically, dietary inclusion of 2%, 4%, 6%, and 8% SCP-H16 replaced approximately 9%, 18%, 27%, and 36% of the soybean meal in the starter diet and 10%, 21%, 31%, and 41% in the grower diet, respectively. The feeding period lasted 42 days. The findings demonstrated that dietary supplementation with SCP-H16 significantly reduced the average daily feed intake and feed conversion ratio of broilers (p < 0.05), without adversely affecting the final body weight and breast meat quality at 42 d. Compared to the CON group, the groups receiving 2% and 4% SCP-H16 exhibited significantly lower serum level of total cholesterol (T-CHO) (p < 0.05). Moreover, the serum activity of total superoxide dismutase (T-SOD) was significantly enhanced in the 2%, 4%, and 6% SCP-H16 groups, and the total antioxidant capacity (T-AOC) was significantly increased in the 2% and 4% SCP-H16 groups (p < 0.05), relative to the CON group. In the liver, glutathione peroxidase (GSH-Px) activity was significantly elevated in the 2% SCP-H16 group compared to the CON group (p < 0.05). Additionally, serum levels of IgG and IgM were significantly elevated in the 2%, 4%, and 6% SCP-H16 groups, while serum IgA level was increased across all SCP-H16-containing groups (p < 0.05). In the liver, both IgG and IgA levels were significantly elevated across all groups receiving SCP-H16 supplementation (p < 0.05). In the duodenum, the 2% SCP-H16 group exhibited a significantly greater villus height compared to the CON group (p < 0.05). Furthermore, in both the duodenum and ileum, the groups receiving 2% and 4% SCP-H16 demonstrated a significant reduction in crypt depth and an increased villus height-to-crypt depth ratio relative to the CON group (p < 0.05). The 2% SCP-H16 group also showed significantly elevated mRNA expression levels of Occludin and zonula occludens-1 (ZO-1) in the duodenum compared to the CON group (p < 0.05). In the ileum, the 2% and 4% SCP-H16 groups exhibited significantly increased Occludin mRNA expression relative to the CON group (p < 0.05), with the 2% SCP-H16 group also showing a significant increase in zonula occludens-1 (ZO-1) mRNA expression (p < 0.05). In conclusion, dietary supplementation with 2% to 4% SCP-H16 is associated with enhanced antioxidant capacity, elevated humoral immunity, and improved intestinal morphology and barrier-related gene expression, suggesting that SCP-H16 can serve as a promising alternative protein source to soybean meal.