Published online by Cambridge University Press: 20 November 2017
In vitro gas systems characterise substrate degradation by estimating fermentation gas release over time. However, as this offers little information regarding feedstuff utilisation, the extent of organic matter degradation (OMD) must be measured to provide an estimate of the metabolizable end-products (VFA and microbial protein) produced. Systems where capacity is limited use either an incubation end-point derived partitioning factor (PF) to estimate degradation from gas or attempt to model OMD stoichiometrically from VFA analyses or assumed gas / VFA relationships. These estimates contain numerous errors. For instance the PF is not constant and the stoichiometric calculations used assume that all OM degraded is carbohydrate composed of hexose sugars. A further potential error is the estimate of the proportion of released gas that originates from VFA neutralisation, as this varies with buffer composition and both proportion and rate (i.e. concentration) of VFA production.
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