Post-experiment correction for release rate in permeation tubes improves the accuracy of the sulphur hexafluoride (SF6) tracer technique in deer

The sulphur hexafluoride (SF6) tracer technique is a means to estimate CH4 emissions from individual ruminants, particularly whilst grazing. The success of the SF6 technique is reliant upon accurate determination of the release rate of SF6 gas from the permeation tubes (PT). Our study aimed to determine effects of SF6 PT rumen residence time on the release rate of SF6 gas and calculated CH4 production (as g CH4/d) in grazing red deer. The CH4 emissions of red deer stags grazing permanent perennial ryegrass based pasture were estimated daily for 5 d at 4.5, 6.5, 9.0 and 11.5 months of age, corresponding to a PT release period of 55, 111, 195 and 258 d. Permeation tube charge time refers to the number of days since PT were charged with SF6. The PT were recovered from 3 deer after the second CH4 measurement and from the remaining 10 deer at the end of the experiment. Release rates of SF6 gas from PT were determined pre-insertion to the rumen (i.e., uncorrected SF6 release rates), or by pre-insertion SF6 release rate with adjustment for SF6 release rates from PT recovered at the termination of the experiment (i.e., corrected SF6 release rates), after the PT had resided in the rumen of red deer for 212 d. A difference of 12.8% between corrected and uncorrected SF6 release rates (P=0.07) occurred after 9 d of PT rumen residence. In contrast, after 65, 150 and 212 d of PT residence, corrected release rates were lower (P<0.05) than uncorrected SF6 release rates by 16, 19.5 and 27%, respectively. Calculated CH4 production and yield (as g CH4/kg dry matter intake) of deer was also reduced by up to 15% (P<0.001) when calculated using corrected versus uncorrected SF6 release rates. Results imply that use of uncorrected SF6 release rates may not be representative of actual SF6 release rate from PT whilst they reside in the rumen. Results also suggest that PT should be recovered upon completion of the experiment and SF6 release rates estimated in order to improve accuracy of calculated CH4 emissions. aper is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors: K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson.