Technical Note: The use of total gas collection for measuring methane production in vented in vitro systems

In previous studies using Ankom GP vented in vitro systems (Ankom Technology, Macedon, NY), methane production was estimated from gas production (GP) and a single gas sample from the incubation vessel's headspace at the end of the incubation. An accurate method requires measurement of methane in the incubation vessel's headspace and in the gases vented over the incubation period. This research aimed to determine whether the act of collecting the gas vented from the Ankom GP system influenced the estimation by the Ankom GP system of the volume of gas produced or the composition of the gas produced. A method involving collecting gas through a long (304 cm), narrow (1 mm i.d.) gas line estimated greater GP than a control method not involving collection of gas. A method involving collecting gas through a short (22 cm), wide (4 mm i.d.) gas line did not affect headspace methane percentage or estimates of GP. It is concluded that in vitro methane production can be accurately estimated by using the Ankom GP system together with collection of vented gases into gas collection bags, but only if the Ankom GP system is connected to the gas collection bag via a short, wide gas line.