Fermentative products and bacterial community structure of C(4) forage silage in response to epiphytic microbiota from C(3) forages

OBJECTIVE: The observation that temperate C(3) and tropical C(4) forage silages easily produce large amounts of ethanol or acetic acid has puzzled researchers for many years. Hence, this study aimed to assess the effects of epiphytic microbiota from C(3) forages (Italian ryegrass and oat) on fermentative products and bacterial community structure in C(4) forage (sorghum) silage. METHODS: Through microbiota transplantation and γ-ray irradiation sterilization, the irradiated sorghum was treated: i) sterile distilled water (STSG); ii) epiphytic microbiota from sorghum (SGSG); iii) epiphytic microbiota from Italian ryegrass (SGIR); iv) epiphytic microbiota from oat (SGOT). RESULTS: After 60 days, all the treated groups had high lactic acid (>63.0 g/kg dry matter [DM]) contents and low pH values (<3.70), acetic acid (<14.0 g/kg DM) and ammonia nitrogen (<80.0 g/kg total nitrogen) contents. Notably, SGIR (59.8 g/kg DM) and SGOT (77.6 g/kg DM) had significantly (p<0.05) higher ethanol concentrations than SGSG (14.2 g/kg DM) on day 60. After 60 days, Lactobacillus were predominant genus in three treated groups. Higher proportions of Chishuiella (12.9%) and Chryseobacterium (7.33%) were first found in silages. The ethanol contents had a positive correlation (p<0.05) with the abundances of Chishuiella, Acinetobacter, Stenotrophomonas, Chryseobacterium, and Sphingobacterium. CONCLUSION: The epiphytic bacteria on raw materials played important roles in influencing the silage fermentation products between temperate C(3) and tropical C(4) forages. The quantity and activity of hetero-fermentative Lactobacillus, Chishuiella, Acinetobacter, Stenotrophomonas, Chryseobacterium, and Sphingobacterium may be the key factors for the higher ethanol contents and DM loss in silages.