In New Zealand methane (CH4) emissions are estimated using the sulphur hexafluoride (SF6) tracer technique. This involves inserting a calibrated source of SF6 gas into the rumen. The technique does not measure CH4 directly but estimates emissions from the ratio of CH4 to SF6 in breath samples collected continuously from above the nose of each animal. Methane estimates obtained using this method tend to be more variable than measurements obtained using respiration calorimetry. The absolute release rate of SF6 from the rumen could contribute to this variation. Data were extracted from a database containing details of 22 separate New Zealand experiments where the SF6 technique was used to estimate CH4. Experiments were divided into four groups according to species and feeding situation, with each group analysed separately. Data were analysed using a linear mixed model with a fixed effect of SF6 release rate, and random effect of experiment. In indoor fed cattle and sheep daily CH4 production was positively related to SF6 release rate (P < 0.05) but there was no relationship between SF6 release rate and daily CH4 production in grazing animals. In grazing sheep and cattle there was no significant effect of SF6 release on CH4 emitted per kg DMI. In cattle kept indoors CH4/kg DMI was positively related to permeation tube flow rate (P < 0.05) but there was no significant effect of SF6 release on CH4 emitted per kg DMI in indoor fed sheep. KEYWORDS: methane; SF6 tracer technique; ruminants.

JB, Vlaming, H Clark, and N Lopez-Villalobos

Proceedings of the New Zealand Society of Animal Production, Volume 65, Christchurch, 3-8, 2005
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