A further method for measuring methane production is the sulphur hexafluoride (SF₆) tracer technique, which requires inserting a known quantity of the inert tracer into the rumen. The use of the SF₆ tracer technique to quantify enteric CH4 emissions from grazing ruminants was pioneered by Zimmerman and Johnson. The SF₆ tracer technique is an indirect method to quantify CH4 emissions from ruminants because only a representative quantity of gas produced by the animal is collected; the emissions are not quantitatively captured as occurs with the respiration chamber (RC) technique, which is the ‘gold standard’ method. Sulphur hexafluoride is considered an ideal tracer gas because it has similar dispersion characteristics in the rumen as CH₄; it is not toxic for the rumen microbes nor the animal and can be measured at very low (trace) amounts. Historically, the SF₆ tracer method generated data with high variability; however, recent modifications to the technique have reduced some of the sources of systemic error and thus the tracer technique can be used with a high degree of accuracy and precision comparable to (RC).

Chapter of the Living Handbook Methods in cattle physiology and behaviour – Recommendations from the SmartCow consortium