possible influence of intra-ruminal sulphur hexafluoride release rates on calculated methane emissions from cattle

Estimates of methane (CH4) production from grazing animals are routinely made using the sulphur hexafluoride (SF6) tracer technique. While this technique is generally regarded as useful, some investigators report a higher variability in measurements when compared with calorimetry. The SF6 technique is a marker dilution method in which a known release rate of SF6 from an intra-ruminal permeation tube is used to calculate CH4 emissions from the ratio of SF6:CH4 in expired breath. The release rate of SF6 is unique for each tube, and although calculated CH4 emissions should be independent of SF6 release rate, an analysis of research conducted in New Zealand has suggested a possible influence of SF6 release rate upon calculated CH4 emissions. A modified cross-over design, with two groups of six steers given either one (2.878 mg SF6 d(-1)) or two (7.336 mg SF6 d(-1)) permeation tubes and offered either energy maintenance (M) or 2 x M levels of feed intake was undertaken to determine the effect of SF6 release rate and intake on calculated CH4 emissions. A high SF6 release rate elevated the calculated CH4 emission per day (P < 0.001) and per kg dry matter intake (kg DMI) by 19% (P < 0.001) irrespective of the level of intake. Release rate of SF6 can affect the calculated CH4 emissions from animals when employing the SF6 tracer technique.