Antimicrobial effects of Black Soldier Fly and Yellow Mealworm fats and their impact on gut microbiota of growing rabbits

Abstract Background The study aimed to evaluate the in vitro antimicrobial activities of two types of insect fats extracted from black soldier fly larvae (HI, Hermetia illucens L.) and yellow mealworm larvae (TM, Tenebrio molitor L.) and their effects as dietary replacement of soybean oil (S) on caecal fermentation pattern, and faecal and caecal microbiota in rabbits. Results A total of 120 weaned rabbits were randomly allotted to 3 dietary treatments (40 rabbits/group): a control diet (C diet) containing 1.5% of S and two experimental diets (HID and TMD) where S was totally substituted by HI or TM fats. Regarding the in vitro antimicrobial activities, HI and TM fats did not show any effects on Salmonella growth. Yersinia enterocolitica showed lower growth when challenged with insect fats than the controls. The insect fat supplementation in rabbit diets increased the contents of the caecal volatile fatty acids when compared to the control group. A metataxonomic approach was adopted to investigate the shift in the microbial composition as a function of the dietary insect fat supplementation. The microbiota did not show a clear separation as a function of the inclusion, even if a specific microbial signature was observed. Indeed, HI and TM fat supplementation enriched the presence of Akkermansia that was found to be correlated with NH3-N concentration. An increase in Ruminococcus, which can improve the immune response of the host, was also observed. Conclusions This study confirms the potential of HI and TM fats as antibacterial feed ingredients with a positive influence on the rabbit caecal microbiota, thus supporting the possibility of including HI and TM fats in rabbit diets.