The use of the Pressure Transducer Technique (PTT) to evaluate feed degradation as described by Theodorou et al (1994) recognises the presence of a lag phase (1-2h) after introducing the microbial innocula to the feed under investigation. Previous work has shown that this can be reduced by incubating the microbes with a basal feed for 24h prior to the addition of a test feed. This work considered the effect of the composition of this basal feed.

Four basal mixtures, Grass silage/conc(G), Hay/cone (H), Maize silage/conc: (M), Whole crop wheat/caustic wheat/cone (W) were prepared plus two mixtures based on purified nutrients to give high Starch (St) and high Cellulose (Ce) contents. 20ml strained, homogenised bovine rumen liquor was added to bottles containing 180ml of media and 1.5g DM of each basal mixture. After 24h of vented incubation at 39°C 1g DM of test feed, (either barley grain or straw both milled to 1 mm) was added and gas production measured at decreasing frequencies over the next 72h. Cumulative gas production at 72h were calculated (Table 1).