The effect of SF_6 release rate, animal species and feeding conditions on estimates of methane emissions from ruminants

摘要

In New Zealand methane (CH_4) emissions are estimated using the sulphur hexafluoride (SF_6) tracer technique. This involves inserting a calibrated source of SF_6 gas into the rumen. The technique does not measure CH_4 directly but estimates emissionsfrom the ratio of CH_4 to SF_6 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 SF_6 from the rumen could contribute to this variation. Data were extracted from a database containing details of 22 separate New Zealand experiments where the SF_6 technique was used to estimate CH_4. Experiments were divided into four groupsaccording to species and feeding situation, with each group analysed separately. Data were analysed using a linear mixed model with a fixed effect of SF_6 release rate, and random effect of experiment. In indoor fed cattle and sheep daily CH_4 production was positively related to SF_6 release rate (P < 0.05) but there was no relationship between SF_6 release rate and daily CH_4 production in grazing animals. In grazing sheep and cattle there was no significant effect of SF_6 release on CH_4 emitted perkg DMI. In cattle kept indoors CH_4/kg DMI was positively related to permeation tube flow rate (P < 0.05) but there was no significant effect of SF_6 release on CH_4 emitted per kg DMI in indoor fed sheep.