Soybean oligosaccharides attenuate odour compounds in excreta by modulating the caecal microbiota in broilers

Abatement of odour emissions in poultry production is important to ensure the quality and safety in the poultry industry as well as for the benefit of the environment. This study was conducted to compare the effects of supplementation with different amounts of dietary soybean oligosaccharides (SBO) and chlortetracycline (CHL) on the major odour-causing compounds in the excreta and on the caecal microbiota in broiler chickens. One-day-old broiler chickens were subjected to a 42-day experiment involving 6 treatments with 6 replicates per treatment (10 birds/cage). The treatments were as follows: negative control (NC; basal diet), positive control (PC; basal diet supplemented with CHL) and basal diet supplemented with 0.5, 2.0, 3.5 and 5.0 g/kg SBO (0.5SBO, 2.0SBO, 3.5SBO and 5.0SBO, respectively). Fresh excreta were sampled for the analysis of odour compounds by HPLC. Caecum content was collected for the caecal microbiota analysis through 16S rRNA sequencing. Results showed that on day 42, the excreta indole concentration in the broilers fed with 2.0SBO, 3.5SBO and 5.0SBO and PC was significantly decreased (P < 0.01) compared with that in the NC-fed broilers. The excreta skatole concentration (P < 0.001) and pH (P < 0.05) were also decreased by SBO and CHL, and they were lowest in birds fed with 3.5SBO. The formate concentrations in birds fed with 3.5SBO and 5.0SBO were higher than those in birds fed with the other diets (P < 0.001). Similarly, acetate concentration (P = 0.003) was increased in birds fed with 3.5SBO. Deep sequencing of 16S rRNA revealed that the composition of the caecal microbial digesta was slightly or significantly changed by the SBO or by the CHL supplementation, respectively. The SBO supplementation decreased the abundance of Bacteroides, Bilophilaand Escherichia, which were associated with the skatole and indole concentrations in the excreta. By contrast, the CHL supplementation demonstrated a strong tendency to enrich Ruminococcus and to reduce the abundance of Rikenella. These results indicated that supplementation with dietary SBO is beneficial in attenuating the concentration of odour-causing compounds and that it modulates the composition of caecal microbiota in broiler chickens.