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.
Stability of Formaldehyde Calibration Gas by Permeation Tube Using Paraformaldehyde