Alternative nutritional evaluation of black soldier fly with various substrates in cat diets and its effects on fecal microbiota

This study aimed to examine the effects of proper substitution ratios and organic substrates of black soldier fly larvae (Hermetia illucens larvae; HIL) on cats. A total of 30 mixed-sex domestic cats (Felis domestica) with an initial body weight of 5.06 ± 0.89 kg were used in this experiment, which used an incomplete 5 × 5 replicated Latin square design. The experimental period was 10 d, with 7 d of diet adaptation followed by 3 d of dietary treatment. The dietary treatments were provided: 1) CON (basal diet), 2) HA3 (replacing 3% of the poultry meal (PM) in the basal diet with HIL fed on animal-based substrate), 3) HA6 (replacing 6% of the PM in the basal diet with HIL fed on animal-based substrate), 4) HP3 (replacing 3% of the PM in the basal diet with HIL fed on plant-based substrate) 5) HP6 (replacing 6% of the PM in the basal diet with HIL fed on plant-based substrate). The HA3 group showed significantly higher (p < 0.05) crude protein digestibility than the CON group. The groups replaced by HIL had significantly higher (p < 0.05) ether extract digestibility than the CON group. The leucine, tryptophan, serine, and aspartic acid digestibility were significantly increased (p < 0.05) in the groups replaced by HIL compared to the CON group. The HP6 group showed distinct (p < 0.05) unweighted UniFrac distances from all other groups and weighted UniFrac distances from the CON and HP3 groups. In addition, the CON group exhibited significant differences (p < 0.05) in weighted UniFrac distances compared to all treatment groups. At the genus level, the HP6 group showed increased (p < 0.05) abundance of Bacteroidota compared with the CON group, while the CON exhibited higher (p < 0.05) levels of Firmicutes than the HP6 group. In conclusion, substituting PM with HIL in cat diets improved nutrient digestibility and had no negative impact on the fecal microbiota. Therefore, it is considered safe and effective to substitute up to 6% of the protein source with HIL in cat diets.