Effect of Insect Live Larvae as Environmental Enrichment on Poultry Gut Health: Gut Mucin Composition, Microbiota and Local Immune Response Evaluation

SIMPLE SUMMARY: Hermetia illucens (HI) and Tenebrio molitor (TM) are considered innovative protein sources in animal nutrition. Recently, it has been discovered that low doses of insect meal can also act as gut prebiotics, providing an alternative to antibiotics. This is extremely relevant to the enhancement of gut health, specifically the absence, avoidance and prevention of gastrointestinal diseases in order to maintain animal welfare, health and performance. Insect meals have been proven to be effective in modulating gut morphometry, mucin composition and microbiota. However, no studies are available on the effects of live insect larvae. For these reasons, this study describes for the first time the effects of low doses of HI and TM live larvae as environmental enrichment on chicken mucin expression, local immune response and microbiota composition. The results herein obtained demonstrated that live insect larvae administered based on 5% of the expected daily feed intake did not impair mucin expression or local cytokine production. Furthermore, it seemed to produce a slight improvement of the caecal microbiota by enhancing a minor fraction of potentially beneficial taxa able to produce short chain fatty acids as an important source of energy for the enterocytes. ABSTRACT: The aim of this study was to evaluate the effect of Hermetia illucens (HI) and Tenebrio molitor (TM) live larvae as environmental enrichment on the mucin composition, local immune response and microbiota of broilers. A total of 180 four-day-old male broiler chickens (Ross 308) were randomly allotted to three dietary treatments (six replicates/treatment; ten animals/replicate): (i) control (C); (ii) C+HI; (iii) C+TM. Live larvae were distributed based on 5% of the expected daily feed intake. At slaughter (39 days of age), samples of duodenum, jejunum and ileum (twelve animals/diet) were submitted to mucin histochemical evaluation. Expression of MUC-2 and cytokines was evaluated by rt-qPCR in jejunum. Mucin staining intensity was not influenced by diet (p > 0.05); however, this varied depending on the intestinal segment (p < 0.001). No significant differences were recorded for IL-4, IL-6 TNF-α, MUC-2 and INF-γ gene expression in jejunum, while IL-2 was lower in the TM group compared to HI and C (p = 0.044). Caecal microbiota showed higher abundance of Clostridium, Saccharibacteria and Victivallaceae in the HI group, while Collinsella was higher in the TM group. The results suggested that live insect larvae did not impair mucin composition or local immune response, and can slightly improve caecal microbiota by enhancing a minor fraction of short chain fatty acid-producing taxa.