Comparison of rumen in vitro fermentation of temperate pastures using different batch culture systems

In vitro batch culture systems are popular because they are relatively inexpensive and allow the screening and testing of large amounts of samples in a short time. Most of the batch culture systems have been designed for the evaluation of gas produced during fermentation of substrates and different designs have been compared between laboratories, but very little work is published where methane production or volatile fatty acid production is compared. The aim of this study was to determine the degree of agreement between two different in vitro batch culture systems, from different laboratories when measuring in vitro fermentation kinetics and end products using pasture samples as substrates. The two systems were a manual and a fully automated pressure-based system. Duplicates of pasture samples were incubated in three consecutive runs. Concordance correlation coefficients between systems and estimates of variance components (pasture, incubation run and random error) for each system were determined for all measured variables. There were poor correlations between systems for most of the variables except for time to produce half of the asymptotic gas production and acetate molar proportion of volatile fatty acids. However, for both systems most of variance was due to pasture sample and then incubation run. The poor agreement between systems might be explained by the different laboratory protocols. Therefore, comparisons of absolute values from different batch culture systems or experiments must be done carefully. Alternatively, more standardisation in terms of sample preparation and incubation procedure may be needed to compare in vitro fermentation products among systems.