Accuracy of SF 6 tracer technology and alternatives for field measurements

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Abstract
The SF6 tracer technique allows methane production from individual grazing ruminants to be measured by placing a calibrated source of SF6 (a permeation tube) in the rumen and determining the ratio of methane to SF6 in the animal's breath. The technique can provide estimates of methane production that are comparable with those determined by respiration calorimetry provided careful attention is paid to the details of permeation tube calibration, gas collection procedures, and gas analysis. The SF6 technique indicates that most of the variation occurring in methane production in the grazing situation is between animals, with small but significant differences between sampling days. Three types of mass balance techniques have also been used, where average methane production is measured outdoors from air flowing across a group of animals. Good agreement can be achieved between these types of techniques and SF6 measurements. The advantage of the SF6 technique for animal scientists is that it can be used under normal grazing conditions and data can be obtained from individual animals thus allowing treatment comparisons to be made. The SF6 technique therefore provides an opportunity for countries whose methane emissions derive predominantly from grazing livestock to obtain accurate estimates of emission and to develop mitigation options.