The effect of sample processing on gas production profiles obtained using the pressure transducer technique

This research considers the effects of feedstuff processing (drying, fractionation and particle size) on the resultant fermentation characteristics of the feed. The effect of drying was investigated using fresh perennial ryegrass (Lolium perenne) or samples that had been microwave, freeze or oven dried. Methods of drying had no effect on dry matter (DM) loss, gas and volatile fatty acid (VFA) production profiles, although fresh grass produced significantly less gas (P<0.05) but with similar values for DM loss and VFA production. The effect of particle size was investigated using naked oats (Avena nuda) and perennial ryegrass hay. Naked oats were divided into whole, half, quarter, coarsely- and finely-ground particles, whilst the hay sample was dry-ground through a 4 mm mesh and then fractionated by wet-sieving through the following mesh sizes; 2.4, 1.2, 0.6, 0.3 and 0.15 mm. With the exception of whole naked oats, where fermentation was minimal, there was little difference between gas production profiles for the different particle sizes of naked oats. In contrast, gas production from the hay particles showed distinct differences in that the smallest particles produced most gas with lesser amounts produced as particle size increased. Similarly, DM loss and VFA production were reduced after incubation of the larger hay particles compared to the smaller particles. From these results, we have concluded that sample processing (grinding and fractionation) can have a significant affect on DM loss, VFA production and the gas production profiles obtained using the pressure transducer technique (PTT) and this must be taken into account when extrapolating to the situation in vivo.