Theodorou et al. (1994) using a manual pressure transducer technique observed a linear response to substrate concentration (cone.) in gas production (GP; ml absolute) whilst lag time and rate of GP values remained constant. This experiment investigated the effect of increasing the cone, of maize starch (S) and milled (1mm) dried grass (DG) on the GP profile using an automated GP technique (Cone 1994).

Either 0.1, 0.25, 0.5, 1.0 or 2.0 g of S or DG were weighed into 250 ml bottles and pre-soaked with anaerobic buffer (85 ml). The bottles were connected to a data logger/pressure tranducer unit and gassed with carbon dioxide. Incubation (39°C) started ∽16 h later when strained rumen fluid was injected into each bottle (15 ml) and a data logger initiated. When GP had ceased the final pH of each bottle was measured and 25 ml of 1M H3PO4 added to stop further enzymic activity. DG bottles were filtered to determine organic matter (OM) residue and hence OM degraded (OMD).