Partial and Total Substitution of Soybean Meal with Black Soldier Fly Larvae Meal in Japanese Quail Diets: Effects on Performance Criteria and Feed Cost Scenarios

The aim of this study was to evaluate the effects of graded replacement of soybean meal (SBM) with black soldier fly larvae meal (BSFLM) on growth performance, growth dynamics, carcass characteristics, and economic efficiency in Japanese quails (Coturnix japonica). A total of 300 one-day-old quail chicks were randomly allocated to five dietary treatments in which SBM was replaced with BSFLM at 0, 25, 50, 75, or 100% using isocaloric and isonitrogenous diets. Body weight was recorded weekly, feed intake was measured per cage, and growth dynamics were assessed using the Gompertz growth model. At 42 d of age, 150 quails were slaughtered to determine carcass yield and major carcass components, and economic evaluation was performed using scenario-based analyses to compare feed cost efficiency under contrasting ingredient price conditions. Dietary inclusion of BSFLM had no significant effects on body weight at any measured age, mortality rate, or carcass yield and composition. Feed intake and feed conversion ratio were significantly improved at the 50% BSFLM inclusion level, indicating improved feed efficiency at moderate replacement. Gompertz growth parameters, including mature weight, growth rate, and inflection point traits, were not affected by dietary treatment, confirming that intrinsic growth patterns were maintained. Economic analyses showed that partial replacement of SBM with BSFLM was associated with improved or stabilized feed cost efficiency depending on relative ingredient prices, whereas higher inclusion levels were more sensitive to unfavorable price conditions. In conclusion, BSFLM can be incorporated into Japanese quail diets without detrimental effects on growth performance or carcass traits, with moderate inclusion levels providing the most consistent balance between biological efficiency and economic robustness, thereby supporting risk-aware and sustainable poultry feeding strategies under variable market conditions.