An evaluation of the face mask system based on short-term measurements compared with the sulfur hexafluoride (SF6 ) tracer, and respiration chamber techniques for measuring CH4 emissions

The objective of the present study was to compare the short term measurement (30 min/day for 3 days) face mask system (FM), with SF6 tracer and respiration chamber (RC) techniques for measuring CH4 emissions from crossbred (Holstein × Gyr) yearling bulls fed at three intake levels. Data were derived from 17 individuals in a completely randomized design experiment in a repeated measures scheme. Bulls were fed a diet consisting of 59.6% corn silage and 40.4% concentrate on a DM basis at three levels of DM intake (DMI) of 1.2% of BW, 1.8% of BW and ad libitum. After an adaptation period, CH4 emissions were measured first using the SF6 tracer technique, followed by the FM and RC techniques, respectively. Daily CH4 emission (g/day) from bulls differed (P < 0.007) with CH4 measurements techniques, with highest emissions measured using RC (107.9 ± 15.36), followed by FM (103.2 ± 11.86) then SF6 tracer technique (87.9 ± 10.16). The CH4 emissions adjusted for differences in DMI and BW did not differ among techniques, averaging 21.5 g/kg DMI and 0.4 g/kg BW, respectively. Total CH4 emissions (g/day) were positively correlated with DMI as measured by all three techniques (SF6r = 0.93; FM r = 0.93; RC r = 0.96). The concordance correlation coefficient (CCC) for CH4 emission (g/d) were 0.82, 0.82 and 0.74 for comparisons of SF6vs RC, FM vs RC and FM vs SF6, respectively. The day-to-day (21.3%) and animal-to-animal (13.4%) variation in CH4 yield (g/kg DMI) was greater from bulls using the FM technique, compared to SF6 (18.8% and 6.8%, respectively) and RC (12.9% and 7.5%, respectively) techniques. We conclude that the short-term FM technique generated CH4 measurements that were comparable to those estimated using SF6 and chamber techniques across a range of DMI levels. However, the FM method may have limitations in terms of assessing enteric CH4 mitigation strategies that are applied over a short duration to low numbers of animals due to higher animal-to-animal and day-to-day coefficients of variation than either the SF6 or RC techniques.