Processing-Dependent Effects of Black Soldier Fly Larvae on Nutrient Digestibility, Palatability, And Fecal Microbiota in Cats

This study evaluated the effects of two drying methods (microwave drying and hot-air drying) for black soldier fly larvae (Hermetia illucens; HI) on nutrient digestibility, palatability, and fecal microbiota composition in cats. Three experimental diets were formulated: CON, basal diet; MW, basal diet with 3% poultry meal (PM) replaced by microwave drying HI; HA, basal diet with 3% PM replaced by hot-air drying HI. In Experiment 1, in vitro digestibility was evaluated with 6 replicates per diet. In vitro organic matter (OM) digestibility was significantly higher (p < 0.05) in HA than CON, and crude protein (CP) digestibility was higher (p < 0.05) in HA compared with MW and CON. In Experiment 2, palatability was assessed using the two-bowl test with 18 cats, and no significant differences were observed in any pairwise comparison for feed intake, intake ratio, time to eat, first sniffing, or first eating. In Experiment 3, in vivo apparent total tract digestibility (ATTD) was determined using 12 cats in a replicated 3 × 3 Latin square design. The HA group showed significantly higher in vivo CP digestibility compared with both CON and MW, while ether extract (EE) digestibility tended to be higher in HA (p = 0.063). Fecal microbiota analysis revealed that the Chao1 index was significantly lower (p < 0.05) in MW at 10 d, and unweighted UniFrac analysis showed significant community separation. At the genus level, Prevotella significantly decreased (p < 0.05) with HI inclusion, while uncultured bacterial taxa were significantly lower (p < 0.05) in both HI groups. These results suggest that hot-air dried HI at 3% inclusion level is a viable alternative protein source for cat diets, offering improved CP digestibility without compromising palatability, while inducing selective shifts in fecal microbiota composition.