Influence of rumen fluid and substrate concentration on fermentation kinetics measured with a fully automated time related gas production apparatus

A new fully automated time related gas production apparatus is presented to study fermentation kinetics in rumen fluid. The newly designed apparatus makes use of electronic pressure transducers in combination with electric valves to release overpressure during the incubation. In this very sensitive system, no gas accumulation and pressure build up takes place. Each valve opening represents a certain amount of gas, set at about 0.7 ml. By recording the number of valve openings in time the kinetics of degradation can be studied. The new equipment was used to study the influence of substrate concentration and source of rumen fluid on fermentation kinetics of grass, corn cob mix (CCM) and corn silage (CS). With the equipment, highly accurate cumulative gas production curves were obtained. In some cases differences between different curves could be made more comprehensive by plotting the rate of gas production against time. The gas production curves were fitted with a multi-phasic model. The shape of the gas production curve was influenced by the chemical composition of the substrate, the ration of the donor animal, the adaptation of the donor animal to a ration, the time of obtaining the rumen fluid from the donor animal and the concentration of the substrate.