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

Abstract

Estimates of methane (CH 4 ) production from grazing animals are routinely made using the sulphur hexafluoride (SF 6 ) tracer technique. While this technique is generally regarded as useful, some investigators report a higher variability in measurements when compared with calorimetry. The SF 6 technique is a marker dilution method in which a known release rate of SF 6 from an intra-ruminal permeation tube is used to calculate CH 4 emissions from the ratio of SF 6 :CH 4 in expired breath. The release rate of SF 6 is unique for each tube, and although calculated CH 4 emissions should be independent of SF 6 release rate, an analysis of research conducted in New Zealand has suggested a possible influence of SF 6 release rate upon calculated CH 4 emissions. A modified cross-over design, with two groups of six steers given either one (2.878 mg SF 6 d -1 ) or two (7.336 mg SF 6 d -1 ) permeation tubes and offered either energy maintenance (M) or 2 × M levels of feed intake was undertaken to determine the effect of SF 6 release rate and intake on calculated CH 4 emissions. A high SF 6 release rate elevated the calculated CH 4 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 SF 6 can affect the calculated CH 4 emissions from animals when employing the SF 6 tracer technique. Key words: Methane, SF 6 tracer technique, cattle, variability, feeding level