A Comprehensive Assessment of Replacing Soybean Meal with Candida Utilis-Fermented Corn Steep Liquor in Broiler Diets: Nutritional Evaluation, Growth Performance, Nutrient Digestibility, Intestinal Health and Serum Biochemical

This study aimed to systematically evaluate the potential of Candida utilis-fermented corn steep liquor (CU-FCSL) to replace soybean meal (SBM) in broiler diets. A total of 72 twenty-one-day-old Arbor Acres Plus broilers (six replicates of six birds) were fed basal or test diets (20% substitution) to determine metabolizable energy. The same design was used to determine standardized ileal amino acid digestibility (SID), with an additional nitrogen-free diet group. In a 42-day growth trial, 288 one-day-old broilers were assigned to control, 2%, 4%, or 6% CU-FCSL diets (six replicates of 12 birds). The results showed that CU-FCSL contained AME 11.36 MJ/kg DM and AMEn 11.31 MJ/kg DM, including SID values of Lys (90.00%), Met (94.01%), Thr (84.63%), and Val (88.86%). Compared with the control, broilers fed 2% or 4% CU-FCSL consistently exhibited greater body weight and weight gain across all phases, whereas 6% inclusion impaired growth performance (p < 0.05). The 4% level improved ether extract digestibility, immune parameters, and intestinal villus height-to-crypt depth ratio, whereas 6% inclusion increased abdominal fat, elevated serum uric acid and ALT, decreased serum IgG, IgM, and IL-10, and inhibited intestinal development and health. In conclusion, 2% and 4% CU-FCSL could be added to replace SBM without adverse effects on broiler health.