Published online by Cambridge University Press: 27 February 2018
At the DLO Institute for Animal Science and Health (ID-DLO) in Lelystad a fully automated time related gas production apparatus has been developed, using sensitive electronic pressure transducers in combination with electric micro-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 known amount of gas, set at about 0-5 ml. By recording each valve opening the kinetics of degradation can be studied. Routine analyses are performed with rumen fluid from wether sheep, diluted with buffer (1 volume rumen fluid/2 volumes buffer). The gas production profiles are fitted with a multi-phasic model, which exists for most foods of three subcurves. It is shown that the first subcurve of gas production is caused by fermentation of the soluble fraction of a food, whereas the second subcurve is caused by fermentation of the non-soluble fraction. The third subcurve, starting after about 15-20 h of incubation, is not related to fermentation of the substrate, but is caused by gas production in the rumen fluid itself, as it is also observed in rumen fluid without substrate. It is discussed whether gas production profiles should be corrected for a blank or not. Gas production profiles of substrates with a high content of protein should be corrected for ammonia synthesis, as the ammonia inhibits the release of gas from the saturated carbonate buffer. The used gas production technique and the used three-phasic curve fit model show a high relationship with existing food evaluation techniques, like the Tilley and Terry technique and the nylon bag technique. Comparing the gas production technique with in vivo data has only been done with a very limited number of samples. At ID-DLO the gas production technique is used at present as a research instrument to study the fermentation characteristics of ruminant foods, the technique is used in breeding programmes of grass and maize, to search for optimal degradable genotypes, and in silage research. Moreover, the technique is used to study rumen physiology, with special emphasis on carbohydrate and protein fermentation and the balance between both. The gas production technique proved to be a cheap and accurate technique to determine differences in fermentation kinetics. The gas production equipment cannot only be used to study the fermentation in the rumen but can be used to study all kinds of fermentation, such as colon fermentation in all kind of animals and humans.
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