[In vitro studies on glycerol transformation by rumen microorganisms]

Rumen fluid from sheep (non adapted to glycerol) was incubated up to six hours under anaerobic conditions with buffer and mineral solution. Wheat starch was added as substrate in an amount of 1g DM per vessel. Glycerol was additionally admitted to rumen fluid in amounts of 5 to 50% of starch. Carrier-free 14C-glycerol (1.3-labelled) or 15N-labelled NH4Cl were added to different incubation vessels. The disappearance rate of glycerol depended from the amount of added glycerol and incubation time. More than 90% of glycerol disappeared in 2 hours (5% addition), 4 hours (10% addition) and 6 hours (15 to 25% addition) respectively. The sum of volatile fatty acids elevated significant with a higher glycerol addition and 6 hours incubation time. The concentration of propionic acid increased also in dependence of the added glycerol amount and the longer incubation time. The proportion of acetic acid to propionic acid changed from high values (3.5 to 4.0, without glycerol) to the lowest value from 2.5 after 6 hours incubation time and 25% glycerol addition. The most radioactivity of added 14C-glycerol was found in propionic acid and only up to 11% in CO2. 14C-radioactivity was not detected in methane, lactic acid and acetic acid respectively. The 15N-labelling of TCA-precipitable N-fraction was not influenced by glycerol supplementation but the 15N-incorporation in the bacterial nitrogen fraction was lower in the vessels with glycerol.