title: Assessment of the sulfur hexafluoride (SF6) tracer technique for measuring enteric methane emissions from cattle.
abstract: A commonly used method of measuring enteric methane (CH4) emissions from ruminants is the SF6 tracer technique that measures respired and eructated CH4. However, within the animal, a small proportion of CH4 is produced post-ruminally and some of this may escape through the rectum. The comparison of emissions using a chamber technique that measures all enteric CH4 losses, and the SF6 tracer technique, could give some insight into the magnitude of post-ruminal emission. The objective of our study was to assess the precision and accuracy of the SF6 tracer technique against a chamber technique for cattle fed a range of diets. Using a repeated-measures design, eight beef heifers were offered a high grain or high forage diet for ad libitum or restricted (65% of ad libitum) feed intake to vary the site of digestion within the gastrointestinal tract (n = 24). The SF6 tracer technique underestimated CH4 emissions on average by 4% relative to the chamber technique. This difference was not significant (P > 0.05) and suggests low post-ruminal CH4 emissions. There was a trend for greater accuracy and precision of the SF6 tracer technique when used with cattle fed a high forage diet at a restricted level of intake. The high forage diet corresponds to the conditions of cattle grazing pasture, suggesting the SF6 tracer technique is most reliable for the grazing system.
authors.affiliation: Agriculture and Agri-Food Canada, P.O. Box 3000, Lethbridge, AB, Canada T1J 4B1. mcginns@agr.gc.ca
authors.forename: S M
authors.initials: SM
authors.lastname: McGinn
authors.forename: K A
authors.initials: KA
authors.lastname: Beauchemin
authors.forename: A D
authors.initials: AD
authors.lastname: Iwaasa
authors.forename: T A
authors.initials: TA
authors.lastname: McAllister
mesh_terms: D000393:Air Pollutants / Q000032:analysis* / Q000737:chemistry; D000821:Animal Feed; D000822:Animal Husbandry; D000818:Animals; D002417:Cattle / Q000254:growth & development / Q000378:metabolism; D004784:Environmental Monitoring / Q000379:methods; D005069:Evaluation Studies as Topic; D006799:Housing, Animal; D008697:Methane / Q000032:analysis* / Q000096:biosynthesis / Q000737:chemistry; D012680:Sensitivity and Specificity; D013459:Sulfur Hexafluoride / Q000032:analysis* / Q000494:pharmacology
chemical_list: D000393:Air Pollutants; D008697:Methane; D013459:Sulfur Hexafluoride