Gut microbiota dynamics in broiler chickens fed insect-based diets

Introduction. Several diet-, host-, and environmental-related factors may influence the chicken gut microbiota [1]. Dietary insect meal inclusion has been reported to positively modulate the gut microbiota of free-range chickens [2], but data in broilers are still limited. This study investigated the effects of Tenebrio molitor (TM) and Hermetia illucens (HI) meal utilization on gut microbiota of broiler chickens. Animals, material and methods. A total of 160 male (trial 1), 160 female (trial 2) and 256 male (trial 3) 1-day-old broiler chickens were randomly allotted to four dietary treatments (control feed [C] and 5, 10 and 15% TM [trial 1 and 2] or HI [trial 3] meal inclusion, with 5 [trial 1 and 2] and 8 [trial 3] replicate pens/treatment and 8 birds/pen). The animals were slaughtered at 53 (trial 1), 40 (trial 2) and 35 (trial 3) days of age. The gut microbiota was assessed on cecal content samples by 16S rRNA amplicon based sequencing. Data were analyzed by R software (Wilcoxon rank sum, Adonis and ANOSIM tests, p value < 0.05; Pairwise Kruskal-Wallis test, False Discovery Rate [FDR] < 0.05). Results and discussion. No differences were found between C- and TM-fed broilers of trial 1 and 2 alpha-diversity measures, while birds fed 15% HI in trial 3 showed lower Shannon index than the others. Concerning beta-diversity, a clear separation of the cecal microbiota due to insect meal utilization was observed in all the trials. At phylum level, the trial 1-broilers fed 15% TM showed decreased abundance of Firmicutes (which has an important role in feed digestion [2]) and lower Firmicutes:Bacteroidetes ratio (which is associated with a high capacity of energy harvesting [2]) when compared to C diet. Similarly, trial 2-birds fed 10 and 15% TM displayed decreased abundance of Firmicutes and lower firmicutes:Bacteroidetes ratio than 5%. At genus level, trial 1-broilers fed TM-diets showed a decrease in the abundance of Clostridium, Coprococcus, L-Ruminococcus and Ruminococcus (predominant, short chain fatty acid [SCFA]-producing bacteria [2]) in their cecal community (with their reduction being particularly evident in animals fed 10 and 15% TM). Differently, TM-fed birds of trial 2 showed an increase in the abundance of Clostridium, Sutterella and Alistipes, along with a lower percentage of Ruminococcus. In trial 3, Clostridium, L-Ruminococcus, Faecalibacterium and Blautia (the latter two being SCFA-producing bacteria [3,4]) were found to be characteristic of the cecal microbiota of 5% HI-fed broilers. Differently, birds fed 10 and 15% HI were characterized, respectively, by Lactobacillus and Ruminococcus, and Bacteroides, Roseburia and Helicobacter (the latter one comprising bacteria with mucolytic activity [5]). Conclusion. Dietary TM and HI meal utilization at low inclusion levels (i.e., 5%) positively modulated the cecal microbiota of the broiler chickens (improved phylum profile and selection of potential beneficial bacteria). However, high inclusion levels (especially the 15%) may have a negative influence (reduction of alpha-diversity,worsened phylum profile, reduction of potential beneficial bacteria and selection of mucolytic bacteria). References: [1] Kers et al. (2018) Front. Microbiol. 9:235; [2] Biasato et al. (2018) BMC Vet. Res. 14:383; [3] Louis and Flint (2009) FEMS Microbiol. Lett. 294:1-8; [4] Liu et al. (2008) Int. J. Syst. Evol. Microbiol. 58:1896-1902; [5] Deplancke and Gaskins (2001) Am. J. Clin. Nutr. 73:1131S-1141S.