Nutritional Evaluation of Fermented Delonix Regia Seed Meal as a Substitute for Soybean Meal in Matured Rabbit Diets: Impact on Growth Performance and Feed Efficiency

Abstract

This study evaluated the impact of substituting soybean meal with Fermented Delonix regia Seed Meal (FDRSM) on the growth performance and nutrient digestibility of  rabbits. Fifty rabbits were randomly assigned to five isonitrogenous and isocaloric dietary treatments: T1 (0% FDRSM), T2 (7.5%), T3 (15.0 %), T4 (22.5 %), and T5 (30.0 % replacement of soybean meal). The FDRSM used in the formulation contained 31.05 % Crude Protein and 2756.3 kcal/kg Metabolizable Energy, alongside potent bioactive phenols and flavonoids unlocked through solid-state fermentation. Results demonstrated a significant (P<0.05) improvement in growth indices as the level of FDRSM increased. Rabbits in T5 recorded the highest final body weight and average daily weight gain, while those in T1 showed the lowest. Feed intake followed a similar upward trend (T5 > T2–T4 > T1), indicating that fermentation enhanced the palatability of the seeds. Conversely, the Feed Conversion Ratio (FCR) was most efficient (lowest) in T5, suggesting superior nutrient utilization. Nutrient digestibility coefficients for Dry Matter (DM), Crude Protein (CP), Ether Extract (EE), and Ash were significantly higher in the FDRSM-supplemented groups (T2–T5) compared to the control. The enhanced digestibility of CP and Ash is attributed to the degradation of anti-nutritional factors like phytates (reduced to 0.12 mg/g) during fermentation, which increased mineral and amino acid bioavailability. Interestingly, Crude Fibre (CF) digestibility was higher in T1, reflecting the lower fiber load and higher nutrient density of the FDRSM-based diets. It is concluded that Fermented Delonix regia seed meal can effectively replace soybean meal by up to 30.0% in rabbit diets, serving as a functional protein source that optimizes both growth kinetics and digestive efficiency.