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Title: Use of a portable, automated, open-circuit gas quantification system and the sulfur hexafluoride tracer technique for measuring enteric methane emissions in Holstein cows fed ad libitum or restricted

Author
item DORICH, CHRISTOPHER - University Of New Hampshire
item VARNER, RUTH - University Of New Hampshire
item PEREIRA, ANDRE - University Of New Hampshire
item MARTINEAU, ROGER - Agri Food - Canada
item Soder, Kathy
item BRITO, ANDRE - University Of New Hampshire

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/2014
Publication Date: 2/4/2015
Citation: Dorich, C.C., Varner, R.K., Pereira, A.B., Martineau, R., Soder, K.J., Brito, A.F. 2015. Use of a portable, automated, open-circuit gas quantification system and the sulfur hexafluoride tracer technique for measuring enteric methane emissions in Holstein cows fed ad libitum or restricted. Journal of Dairy Science. 98(4):2676–2681.

Interpretive Summary: While there are many techniques used to measure methane emissions from ruminants, each has its own set of limitations. In this study a new method, a portable automated head chamber system, was compared against the standard sulfur hexafluoride tracer technique to evaluate methane emissions in lactating dairy cows. Overall, the head chamber method was less variable, with methane emissions more strongly correlated to changes in feed intake, indicating that it may be a more accurate and reliable method. Methane gas data collection may be impacted by barn ventilation; therefore, future research with an improved ventilation system is warranted to further assess these two methodologies.

Technical Abstract: The sulfur hexafluoride tracer technique (SF**6) is a commonly used method for measuring CH**4 enteric emissions in ruminants. Studies using SF**6 have shown large variation in CH**4 emissions data, inconsistencies in CH**4 emissions across studies, and potential methodological errors. Therefore, the purpose of this study was to compare the SF**6 method to a new portable automated open-circuit head chamber system (HC) using mid lactation Holstein cows housed in a tie stall barn. Sixteen cows averaging 176 days in milk, 42.9 kg of milk yield, and 681 kg of body weight were randomly assigned to: 1) restricted intake (90% of dry matter intake), or 2) ad libitum intake according to a crossover design. Each experimental period lasted 22 d with 14 d for treatment adaptation and 8 d for data and samples collection. A common diet was fed to the cows as a total mixed ration and contained 40% corn silage, 12% grass-legume haylage, and 48% concentrate. Spot 5-min measurements using the HC system were taken twice daily with a 12 h interval between samplings with sampling time advanced 2 h daily to account for diurnal variation in CH**4 emissions. Canisters for the SF**6 method were sampled twice daily before milking with 4 local background gas canisters inside the barn analyzed for background gas concentrations. Paired enteric CH**4 emissions from each method were compared by using the concordance correlation coefficient (CCC) on pooled data because regressions of SF**6 against HC were not affected by treatment and period. The CCC between methods was low (less than 5%) either on all individual positive (n = 303) or data filtered (n = 240; 150 to 800 g/d) CH**4 measurements. Accordingly, a lack of concordance (less than 19%) was also observed on paired averages per cow/period calculated from all individual positive (n = 30) or data filtered (n = 29) CH**4 measurements. The coefficient of variation was up to 5 times greater for CH**4 measurements using the SF**6 method compared with the HC system. The lack of concordance and the greater variability associated with SF**6 measurements likely resulted from the poor ventilation in the barn causing high concentrations of background gases.