Effects of short-term fasting on in vivo rumen microbiota and in vitro rumen fermentation characteristics.

Objective: Fasting may lead to changes in the microbiota and activity in the rumen. The objective of the present study was to evaluate the effects of fasting on rumen microbiota and the impact of fasting on in vitro rumen fermentation using molecular culture-independent methods.

Methods: Three ruminally cannulated Holstein steers were fed rice straw and concentrates. The ruminal fluids were obtained from the same steers 2 h after the morning feeding (control) and 24 h after fasting (fasting). The ruminal fluid was filtrated through four layers of muslin, collected for a culture-independent microbial analysis, and used to determine the in vitro rumen fermentation characteristics. Total DNA was extracted from both control and fasting ruminal fluids. The rumen microbiota was assessed using denaturing gradient gel electrophoresis (DGGE) and quantitavtive PCR. Microbial activity was evaluated in control and fasting steers at various intervals using in vitro batch culture with rice straw and concentrate at a ratio of 60:40.

Results: Fasting for 24 h slightly affected the microbiota structure in the rumen as determined by DGGE. Additionally, several microorganisms, including Anaerovibrio lipolytica, Eubacterium ruminantium, Prevotella albensis, Prevotella ruminicola, and Ruminobacter amylophilus, decreased in number after fasting. In addition, using the ruminal fluid as the inoculum after 24 h of fasting, the fermentation characteristics differed from those obtained using non-fasted ruminal fluid. Compared with the control, the fasting showed lower total gas production, ammonia, and microbial protein production (p < 0.05). No significant differences, however, was observed in pH and dry matter digestibility.

Conclusion: When in vitro techniques are used to evaluate feed, the use of the ruminal fluid from fasted animals should be used with caution.