Relationship between gas production and starch degradation in feed samples

An investigation was completed of the possibilities to estimate starch fermentation in rumen fluid using the gas production technique by incubating the total sample. Gas production from six starchy feed ingredients and eight maize silage samples were recorded and related to starch degradation measured after 0, 2, 4, 6, 8, 12, 16, 24 or 32 h incubation in buffered rumen fluid. Maize silage samples and starchy feed ingredients were selected on the basis of their starch content, ranging from 120 to 478 g/kg OM for maize silage and 483–905 g/kg OM for the feed ingredients. The majority of starch degradation occurred after 6 h incubation and was completed within 24 h. A modest relationship was observed between gas production and measured starch degradation (R2=0.80, R.S.D. = 82) for all samples. For the individual starchy feed ingredients and maize silages, the relationship between gas production and starch degradation was much higher (R2=0.96–1.00, R.S.D.=8.9–43.0). Among all samples, accounting for starch content, the relationship between starch degradation and gas production was described by: starch degradation (mg/g OM) = −191.6 (±14.6) + 0.303 (±0.025) × starch content + 1.648 (±0.053) × gas production at incubation time t (R2=0.92, R.S.D. = 51.3). It was concluded that the fermentation of starch and other non-soluble components occurred simultaneously. For individual samples, starch degradation could be reasonably accurately estimated by gas production and starch content, offering a fast and inexpensive alternative of investigating rumen fermentation kinetics in these starchy feedstuffs. Although among feedstuffs starch degradation was less accurately estimated from gas production and starch content, the method is a useful method for fast screening purposes.