Effect of dietary fiber on microbial activity and microbial gas production in various regions of the gastrointestinal tract of pigs

The microbial activity, composition of the gas phase, and gas production rates in the gastrointestinal tract of pigs fed either a low- or a high-fiber diet were investigated. Dense populations of culturable anaerobic bacteria, high ATP concentrations, and high adenylate energy charges were found for the last third of the small intestine, indicating that substantial microbial activity takes place in that portion of the gut. The highest microbial activity (highest bacterium counts, highest ATP concentration, high adenylate energy charge, and low pH) was found in the cecum and proximal colon. Greater microbial activity was found in the stomach and all segments of the hindgut in the pigs fed the high-fiber diet than in the pigs fed the low-fiber diet. Considerable amounts of O2 were found in the stomach (around 5%), while the content of O2 in gas samples taken from all other parts of the gastrointestinal tract was < 1%. The highest concentrations and highest production rates for H2 were found in the last third of the small intestine. No methane could be detected in the stomach or the small intestine. The rate of production and concentration of methane in the cecum and the proximal colon were low, followed by a steady increase in the successive segments of the hindgut. A very good correlation between in vivo and in vitro measurements of methane production was found. The amount of CH4 produced by pigs fed the low-fiber diet was 1.4 liters/day per animal. Substantially larger amounts of CH4 were produced by pigs fed the high-fiber diet (12.5 liters/day). Also, the daily rate of CO2 production in the gut was higher for the pigs fed the high-fiber diet than for the pigs fed the low-fiber diet (212 versus 46 liters/day). Although the highest microbial activity was found in the cecum and proximal colon and although hydrogen production is an obligate part of anaerobic fermentation in the hindgut, only small net amounts of hydrogen were produced in these segments. Furthermore, only small amounts of methane were produced in the cecum and proximal colon. This strongly indicates that hydrogen sinks other than methane production are involved in hydrogen removal in the cecum and proximal colon of pigs.