Gut health in broiler chickens fed a mixture of Hermetia illucens and Tenebrio molitor meals: does it have a key role in shaping bird performance?

Insect meals are promising sustainable protein sources for poultry, but comprehensive insights into their effects on gut health and growth performance are lacking. This study is the first to elucidate relationships between gut health parameters and performance in broilers fed Hermetia illucens (HI) and Tenebrio molitor (TM) meals at 5% or 10% inclusion levels, singly or in a 1:1 combination. A 37-day trial used 420 male Ross 308 chicks randomly allocated to seven treatments: control (C), HI5 (5% HI), HI10 (10% HI), TM5 (5% TM), TM10 (10% TM), MIX5 (5% MIX), and MIX10 (10% MIX). By integrating intestinal histomorphometry, mucin histochemistry, multi-organ histopathology, and multi-omics cecal microbiome characterization, we identified key structural, microbial, and metabolic biomarkers associated with performance variations (false discovery rate [FDR]<0.05 and P < 0.05 for microbiome and histomorphology, respectively). High-performing groups (MIX5, TM5) showed microbiomes enriched in short-chain fatty acid-producing bacteria (Veillonellaceae, Butyricicoccus, Limosilactobacillus crispatus), positively correlated with ADG and ADFI (FDR<0.05) and negatively correlated with FCR (FDR<0.05). Favorable metabolomic profiles (increased dopamine, tyramine, malic and orotic acids; reduced 3-deoxyglucosone, hexanoylcarnitine [FDR<0.05]) and preserved balance between neutral (positively correlated with BW and ADFI [P < 0.05]) and acidic mucins (positively correlated with BW, ADFI and ADG, and negatively correlated with FCR [P < 0.05]) were also observed. Low-performing groups (MIX10, HI10) displayed microbiomes dominated by Ruminococcaceae, Alistipes, and l-Eubacterium (negatively correlated with FCR and associated with purine metabolism alterations [FDR<0.05]), alongside worsened morphology (tendency for reduced villus height in MIX10 [P = 0.07], positively and negatively correlated with ADG and FCR, respectively [P < 0.05], and thinner mucosal/muscular layers [P < 0.05]) and decreased neutral mucins (P < 0.05). TM10 maintained unaffected growth performance via beneficial taxa (Limosilactobacillus crispatus, Tyzzerella), and reduced Campylobacter jejuni and antimicrobial resistance genes (FDR<0.05). Jejunal inflammation, negatively correlated with ADG (P < 0.05), was not influenced by dietary treatments (P > 0.05). In conclusion, specific taxa (Butyricicoccus, Veillonellaceae, Limosilactobacillus crispatus), metabolites (dopamine, tyramine, malic and orotic acids), and mucosal features (villus height, mucin composition) were identified as biomarkers of optimal performance in insect-fed broilers.