Modulation of gut microbiota, morphology and mucin composition by dietary Hermetia illucens meal inclusion in broiler chickens

Dietary modifications have been reported to influence intestinal microbiota, morphology and mucin dynamics in poultry. The present study evaluated the effects of dietary Hermetia illucens (HI) meal inclusion on gut microbiota, morphology and mucin composition in broiler chickens. A total of 192 male broiler chickens were divided into 4 dietary treatments (control feed and 5% [HI5], 10% [HI10] and 15% [HI15] HI meal inclusion) and slaughtered at 35 days of age (12 birds/diet). The gut microbiota was assessed on cecal content samples by 16S rRNA amplicon-based sequencing. Intestinal morphology was evaluated through morphometric measurements of villus height (Vh), crypt depth (Cd) and villus height/crypt depth ratio (Vh/Cd) on duodenum, jejunum and ileum. Small intestine and caecum were also stained with Periodic Acid Schiff, Alcian Blue pH 2.5 and High Iron Diamine to discriminate among neutral, acidic sialylated and acidic sulfated mucins, respectively. L-Ruminococcus, Faecalibacterium, Blautia and Clostridium genera were found to be characteristic of HI5 cecal microbiota (FDR < 0.05), while broiler chickens fed with HI10 and HI15 diets were characterized (FDR < 0.05) by Lactobacillus and Ruminococcus (HI10) and Bacteroides, Roseburia and Helicobacter genera (HI15). HI15 birds showed lower Vh (P < 0.05), higher Cd (P < 0.05) and reduced Vh/Cd (P < 0.01) than the others, with duodenum showing the highest morphometric indices in all the dietary treatments (P < 0.001). Lower mucin staining intensity (P < 0.001) was also observed in the intestinal villi of broilers fed with HI10 and HI15 diets than the others. Independently of HI meal utilization, crypt mucins were predominantly neutral and acidic sialylated and higher in ileum and base fragment (P < 0.001), while villus mucins were predominantly acidic sialylated (P = 0.10) and higher in ileum (P < 0.001). In conclusion, dietary HI meal utilization at 5% inclusion rate may positively modulate the cecal microbiota of broiler chickens without affecting the gut mucosal morphology and mucin composition. On the contrary, increasing levels of dietary HI meal inclusion (especially the 15%) may negatively affect the gut microbiota, mucosal morphology and mucin composition, thus suggesting that lower levels could be preferable.