title: Short communication: 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.
abstract: The objective of this study was to measure enteric CH4 emissions using a new portable automated open-circuit gas quantification system (GQS) and the sulfur hexafluoride tracer technique (SF6) in midlactation Holstein cows housed in a tiestall barn. Sixteen cows averaging 176 ± 34 d in milk, 40.7 ± 6.1 kg of milk yield, and 685 ± 49 kg of body weight were randomly assigned to 1 out of 2 treatments according to a crossover design. Treatments were (1) ad libitum (adjusted daily to yield 10% orts) and (2) restricted feed intake [set to restrict feed by 10% of baseline dry matter intake (DMI)]. Each experimental period lasted 22d, with 14 d for treatment adaptation and 8d for data and sample collection. A common diet was fed to the cows as a total mixed ration and contained 40.4% corn silage, 11.2% grass-legume haylage, and 48.4% concentrate on a dry matter basis. Spot 5-min measurements using the GQS were taken twice daily with a 12-h interval between sampling and sampling times advanced 2h daily to account for diurnal variation in CH4 emissions. Canisters for the SF6 method were sampled twice daily before milking with 4 local background gas canisters inside the barn analyzed for background gas concentrations. Enteric CH4 emissions were not affected by treatments and averaged 472 and 458 g/d (standard error of the mean = 18 g/d) for ad libitum and restricted intake treatments, respectively (data not shown). The GQS appears to be a reliable method because of the relatively low coefficients of variation (ranging from 14.1 to 22.4%) for CH4 emissions and a moderate relationship (coefficient of determination = 0.42) between CH4 emissions and DMI. The SF6 resulted in large coefficients of variation (ranging from 16.0 to 111%) for CH4 emissions and a poor relationship (coefficient of determination = 0.17) between CH4 emissions and DMI, likely because of limited barn ventilation and high background gas concentration. Research with improved barn ventilation systems or outdoors is warranted to further assess the GQS and SF6 methodologies.
authors: Institute for the Study of Earth, Oceans, and Space and Department of Earth Sciences, University of New Hampshire, Durham 03824.
authors: C D
authors: CD
authors: Dorich
authors: Institute for the Study of Earth, Oceans, and Space and Department of Earth Sciences, University of New Hampshire, Durham 03824.
authors: R K
authors: RK
authors: Varner
authors: Department of Biological Sciences, University of New Hampshire, Durham 03824.
authors: A B D
authors: AB
authors: Pereira
authors: Dairy and Swine Research and Development Centre, Agriculture and Agri-Food Canada, Sherbrooke, Québec, Canada J1M 0C8.
authors: R
authors: R
authors: Martineau
authors: Pasture Systems and Watershed Management Research Unit, USDA-Agricultural Research Service, University Park, PA 16802.
authors: K J
authors: KJ
authors: Soder
authors: Department of Biological Sciences, University of New Hampshire, Durham 03824. Electronic address: andre.brito@unh.edu.
authors: A F
authors: AF
authors: Brito
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D000818:Animals; D002417:Cattle / Q000378:metabolism*; D003612:Dairying; D004784:Environmental Monitoring / Q000379:methods*; D005260:Female; D008697:Methane / Q000032:analysis*; D013459:Sulfur Hexafluoride / Q000032:analysis
chemical_list: D000393:Air Pollutants; D008697:Methane; D013459:Sulfur Hexafluoride
keywords: dairy cow; gas quantification system; methane; sulfur hexafluoride tracer technique