Hermetia illucens fat affects the gastrointestinal tract selected microbial populations, their activity, and the immune status of broiler chickens

The present study investigated the effect of Hermetia illucens larvae (BSFL) fat, derived using supercritical CO₂ extraction and added to broiler chickens’ diets as a partial (50%) or total replacement for commonly used soybean oil, on the gastrointestinal tract (GIT) microbial population, its activity, and selected physiological and immune traits. A total of 576 one-day-old female Ross 308 chicks were randomly assigned to 3 dietary treatments with 16 replicates each. The following treatments were applied: SO – 100% soybean oil, BSFL50 – a mixture of BSFL and soybean oils in a 50:50 ratio, and BSFL100 – 100% BSFL fat. Digesta samples from the crop, jejunum and caeca were collected for further analyses, i.e., pH measurements, fluorescent in situ hybridization, and short-chain fatty acid (SCFA) concentrations. Additionally, the selected plasma biochemical parameters and immunological traits were assessed. In general, the implementation of BSFL fat in broilers’ diets resulted in increased proliferation of potentially pathogenic bacterial populations in the crop, such as Enterobacteriaceae, Bacteroides–Prevotella cluster, and Clostridium perfringens. Furthermore, BSFL100 enhanced microbial activity via total SCFA production and lowered the pH in this segment. However, no detrimental effects were observed in terms of other GIT segments, i.e., the jejunal and cecal microecosystems. The strongest impact on reduction of select components of the microbial population in the cecum was observed with the BSFL50 treatment for potentially pathogenic bacteria such as Enterobacteriaceae, Bacteroides–Prevotella cluster, while commensal populations were also limited, i.e., Bacillus spp., C. leptum subgroup, and C. coccoides–Eubacterium rectale cluster. Additionally, BSFL100 reduced the cholesterol concentration in the blood, while both experimental treatments decreased the ALT level. In conclusion, due to the insufficient release of lauric acid from the BSFL fat in the crop, an adverse shift in the microbiota can be noted. However, a positive suppressive effect on the select components of the cecal microbiota, as well as improvement of liver health suggests implying the BSFL fat in broiler nutrition.