Ruminal fermentation and microbial community differently influenced by four typical subtropical forages in vitro

The present study evaluated the effects of 4 typical subtropical forages on ruminal microbial community composition to formulate a better diet for buffalo. Corn straw silage, elephant grass, cassava residues and sugarcane tail silage were used as substrates for in vitro fermentation. Eight replicates were set up for every substrate, and fermentation was carried out in a 100-mL glass syringe, using buffalo rumen inoculum. Every replicate was anaerobically dispensed with 10 mL of rumen inoculum, 20 mL of McDougall's buffer and 200 mg of dried substrate, and placed in a water bath at 39 °C. Gas production was recorded at 0, 2, 6, 12, 24, 36, 48 and 72 h of incubation. After 24 h, fermentation was ceased for 4 replicates and samples were collected. Volatile fatty acids (VFA) concentrations were measured using gas chromatography. Microbial populations were quantified using quantitative real-time PCR (qRT-PCR), and microbial community was analyzed using high throughput sequencing technology. The results showed, cassava residues as substrate had the highest gas production, acetate, propionate and total VFA concentrations (P < 0.05), and corn straw silage had the lowest acetate:propionate ratio (P < 0.05). The lowest numbers of fungi, Ruminococcus albus and Fibrobacter succinogenes, and the highest number of protozoa were observed with cassava residues (P < 0.05). The least abundances of bacterial phyla Firmicutes, Bacteroidetes and genus Prevotella, and substantially higher abundance of phylum proteobacteria (56%) and genus Succinivibrio (52%) were observed with cassava residues. The most abundances of Methanobrevibacter gottschalkii and Entodinium were observed with cassava residues. Spearman's correlations analysis showed, Succinivibrio had strong positive correlations with propionate, butyrate, Metadinium and M. gottschalkii, indicating fermentation products were related to microbial community. In conclusion, incubation with cassava residues resulted in lower number of fiber degrading microbes but higher protozoal population because of its low fiber contents. The microbial community was highly altered by in vitro incubation with cassava residues, whereas remained similar for the other 3 high fiber containing substrates. Keywords: Buffalo rumen inoculum, In vitro fermentation, Subtropical forages, Microbial population, Microbial community