SF6
NOTE: This version of Section 20 has been approved by the working group's Chair. Please be aware that further revisions may occur before final review and approval by the Board and ICAR members per the Approval of Page Process.
The SF6 technique samples breath over 24 hours, whereas other techniques use spot samples of breath over periods of minutes throughout the day, so diurnal variation has to be considered. The majority of CH4 (87-99%) is released by eructation (Blaxter and Joyce, 1963[1]; Murray et al., 1976[2]), which provides a clear signal for sample processing. Please note that the tracheostomy used in Murray et al. (1976)[2] may have resulted in a higher percentage, but in both publications, it is clear that the majority of the CH4 is released via eructation. The SF6 tracer gas technique was developed in an attempt to measure CH4 emissions by animals without confinement in respiration chambers (Johnson et al., 1994[3]). Air is sampled near the animal’s nostrils through a tube attached to a halter and connected to an evacuated canister worn around the animal’s neck or on its back. A capillary tube or orifice plate is used to restrict airflow through the tube so that the canister is between 50 and 70% full in approximately 24 hours. A permeation tube containing SF6 is placed into the rumen of each animal. The pre-determined release rate of SF6 is multiplied by the ratio of CH4 to SF6 concentrations in the canister to calculate CH4 emission rate.
Many research centres have used the SF6 technique with variations in design of sampling and collection equipment, permeation tubes, and gas analysis (Berndt et al., 2014[4]). Reliable results depend on following standard protocols, with greatest variation coming from accuracy of determining SF6 release rate from permeation tubes and control of sampling rate. With capillary tubes, sampling rate decreases as pressure in the canister increases, whereas an orifice plate gives a steadier sampling rate over 24 hours (Deighton et al., 2014[5]). A source of error that has not been evaluated is that animals might interact and share CH4 emissions when the sampling tube of one animal is near the head of another animal. There is good agreement between CH4 emissions measured by the SF6 technique and respiration chambers, although results from the SF6 technique are more variable (Grainger et al., 2007[6]; Muñoz et al., 2012[7]).
- ↑ Blaxter, K.L., and Joyce, J.P. 1963. The accuracy and ease with which measurements of respiratory metabolism can be made with tracheostomized sheep. Br. J. Nutr. 17:523-537
- ↑ 2.0 2.1 Murray, R.M., Bryant, A.M., and Leng, R.A.. 1976. Rates of production of methane in the rumen and large intestine of sheep. Br. J. Nutr. 36:1-14.
- ↑ Johnson, K., Huyler, M., Westberg, H., Lamb, B., and Zimmerman, P. 1994. Measurement of methane emissions from ruminant livestock using a sulfur hexafluoride tracer technique. Environ. Sci. Technol. 28:359-362.
- ↑ Berndt, A., Boland, T.M., Deighton, M.H., Gere, J.I., Grainger, C., Hegarty, R.S., Iwaasa, A.D., Koolaard, J.P., Lassey, K.R., Luo D., Martin, R.J., Martin, C., Moate, P.J., Molano, G., Pinares-Patiño, C., Ribaux, B.E., Swainson, N.M., Waghorn, G.C., and Williams, S.R.O. 2014. Guidelines for use of sulphur hexafluoride (SF6) tracer technique to measure enteric methane emissions from ruminants. Pages 166. M. G. Lambert, ed. New Zealand Agricultural Greenhouse Gas Research Centre, New Zealand.
- ↑ Deighton, M.H., Williams, S.R.O., Hannah, M.C., Eckard, R.J., Boland, T.M., Wales, W.J., and Moate, P.J. 2014. A modified sulphur hexafluoride tracer technique enables accurate determination of enteric methane emissions from ruminants. Anim. Feed Sci. Technol. 197:47-63.
- ↑ Grainger, C., Clarke, T., McGinn, S.M., Auldist, M.J., Beauchemin, K.A., Hannah, M.C., Waghorn, G.C., Clark, H., and Eckard, R J. 2007. Methane emissions from dairy cows measured using the sulfur hexafluoride (SF6) tracer and chamber techniques. J. Dairy Sci. 90:2755-2766.
- ↑ Muñoz, C., Yan, T., Wills, D.A., Murray, S., and Gordon, A.W. 2012. Comparison of the sulfur hexafluoride tracer and respiration chamber techniques for estimating methane emissions and correction for rectum methane output from dairy cows. J. Dairy Sci. 95:3139-3148.
