Comparison of gas accumulation profiles of several feeds using manual or automated gas production methods

The relationship of metabolizable energy (ME) content of the diet to gas production measured by the Hohenheim gas test (HGT) has been studied intensively. However, the HGT is being replaced by automatic systems like the automated pressure evaluation system (APES) and comparison with the HGT method is required before ME estimation can be automated. This study compared the two different gas production methods (HGT and the APES) with regard to the cumulative gas profile. With the APES method, the release of gas may occur at any time, assuming fixed amounts of gas being released for each venting, after reaching fixed values of pressure. With the HGT method manual readings are performed at defined time points. For comparison purposes, gas production was calculated on the basis of ml/200 mg dry matter (DM), as usual in the HGT method. For I I feeds analyzed (grass silage, meadow hay, fresh red clover, fresh birdsfoot trefoil, whole-crop oat silage, maize stover and car maize, dairy compound feed and soybean meal) the APES method produced on average 5.5 ml (range 1.1-8.3 ml/200 mg DM) less gas on average compared to the HGT method (0-120 h incubation time). Reasons for the differences may be related to the measurement conditions of each method itself. The ratio of sample size to rumen fluid (mg/ml) is 20:1 in the HGT method and 100: 1 in the APES method, which may have influenced the colonization rate and contributed to a larger lag phase in APES. The estimates are based on two runs, which were performed on different days, with the APES method generating a large run effect. In conclusion, the amount of gas produced using the APES method deviated consistently from the amounts of gas produced by the HGT method in a large range of gas production (30-72 ml/200 mg DM). Using the laboratory protocol as proposed by each method, the suggested mathematical correction of the gas measured through APES appears applicable for gas production after 24 h, needing a larger number of samples to prove its efficacy. (C) 2008 Elsevier B.V. All rights reserved.