Effects of Single-Cell Protein Derived from Ralstonia eutropha on Growth Performance, Meat Quality, Antioxidant...

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.