Protein composition and digestibility of black soldier fly larvae in broiler chickens revisited according to the recent nitrogen-protein conversion ratio

Specific nitrogen-to-protein (N:P) conversion factors have recently been defined for processed insect meal, because the presence of non-protein nitrogen in insects leads to an overestimation of the insect protein content. The aim of this paper was, on the basis of our previous study, to recalculate the digestibility of partially or totally defatted black soldier fly (BSF; Hermetia illucens) larva meals in broiler chickens. Sixty 26-days-old Ross 308 male chickens were randomly divided into fifteen cages (5 replicates/treatment). The chickens were fed a basal diet, and two BSF larva meal diets that differed according to their fat content. The digestibility trial lasted 10 days, and it included a 6-days adaptation period and 4-days of excreta collection. Four methods were used to recalculate the crude protein (CP) content of the diet and excreta, using either the conventional 6.25 N:P conversion ratio, the mean 5.60 N:P conversion ratio proposed in literature, or the weighted average of the specific N:P conversion ratio (5.62 for BSF meal, 5.68 for corn and 5.64 for soybean meal). The data were analysed using the t-test and differences were considered significant for P<0.05. Diet CP digestibility calculated using the conventional 6.25 N:P conversion factor was slightly lower than that calculated using the weighted average 5.66 and 5.65 N:P conversion factors (P<0.005). A significantly lower diet CP digestibility was found when using the conventional 6.25 N:P conversion factors for the basal diet and excreta and the weighted average 6.09 N:P conversion factors for the insect meal diets (P<0.005). As far as the latest developments pertaining the N:P conversion ratio in processed insect meal are concerned, the mean 5.60 N:P conversion ratio seems more accurate than the conventional 6.25 one to determine the CP content in poultry diets containing insect processed meal.