Effects of Different Yeast Culture Levels on in vitro Ruminal Fermentation Characteristics and Microbial Community of a High Concentrate Diet in Sheep

This research aimed to investigate the effects of different yeast culture (YC) levels in vitro on fermentation characteristics and bacterial and fungal community under high concentrate diet of sheep. A total of five groups were included in the current experiment: control group without YC (CON), YC1 (0.5% YC proportion of substrate dry matter), YC2 (1%), YC3 (1.5%) and YC4 (2%). After 48 h of fermentation, the incubation fluids and residues were sampled to analyze the ruminal fermentation parameters and bacterial and fungal community. Results showed that the ruminal fluid pH of YC2 and YC4 groups was higher (p < 0.05) than that of CON group. Compared with CON group, the microbial protein, propionate and butyrate concentrations and cumulative gas production at 48 h were significantly increased (p < 0.05), whereas an opposite trend of ammonia nitrogen and lactate was observed between CON and YC2 groups. Microbial analysis showed that the Chao1 and Shannon indexes of YC2 group were higher (p < 0.05) than those of CON group. Additionally, YC supplementation significantly decreased (p < 0.05) Succinivibrionaceae_UCG-001, Streptococcus bovis and Neosetophoma relative abundances. An opposite tendency of Aspergillus abundance was found between CON and YC treatments. Compared with CON group, the relative abundances of Prevotella, Succiniclasticum, Butyrivibrio and Megasphaera elsdenii were significantly increased (p < 0.05) in YC2 group, while the Apiotrichum and unclassified Clostridiales relative abundances were decreased (p < 0.05). In conclusion, high concentrate substrate supplemented with appropriate YC (1%) could improve ruminal fermentation and regulate bacterial and fungal composition.