title: Comparison of the sulfur hexafluoride tracer and respiration chamber techniques for estimating methane emissions and correction for rectum methane output from dairy cows.
abstract: The objectives of the present study were to compare the sulfur hexafluoride (SF₆) and respiration chamber techniques for measuring methane (CH₄) emissions from dairy cows and to determine the proportion of CH₄ that is released through the rectum. Data used were derived from 20 early lactation dairy cows in a 2 × 2 factorial design study for 4 periods with 6 wk/period. The 4 treatment diets consisted of grass silage and 2 levels of concentrate (30 and 60% dry matter basis), with or without yeast supplement. At the end of each period, CH₄ emissions were measured simultaneously using the SF₆ and respiration chamber techniques when cows were housed in chambers. The SF₆ technique was also used when cows were housed in digestibility units (barn location) before and after respiratory chamber measurements (chamber location). The simultaneous measurements in chamber location revealed that CH₄ emission estimates by the SF₆ technique were similar to those by the respiration chamber technique in the first 3 periods, although the SF₆ estimates were significantly higher in period 4. The regression of all data from the 4 periods demonstrated a linear relationship between the SF₆ and respiration chamber measurements for total CH₄ emissions (g/d, R² = 0.69) and for CH₄ emissions per unit of milk yield (g/kg, R² = 0.88), and a quadratic relationship for CH₄ emissions per unit of dry matter intake (g/kg, R² = 0.64). The CH₄ emissions from the rectum were calculated as the difference between CH₄ estimates from the SF₆ technique when cows were housed in respiratory chambers and barn locations, which was 3% of the total CH₄ emissions from the mouth, nostrils, and rectum. The SF₆ estimates in the chamber location accounted for all sources of emissions, whereas those in the barn location, like that in grazing conditions, did not include CH₄ emission from the rectum. Therefore, the SF₆ measurements for grazing cattle should be adjusted for CH₄ emissions from the rectum (3% of total). We conclude that the SF₆ technique is reasonably accurate for estimating CH₄ emissions.
authors.affiliation: Agri-Food and Biosciences Institute-AFBI Agriculture Branch, Hillsborough, Co. Down, BT26 6DR, United Kingdom. camila.munoz@inia.cl
authors.forename: C
authors.initials: C
authors.lastname: Muñoz
authors.forename: T
authors.initials: T
authors.lastname: Yan
authors.forename: D A
authors.initials: DA
authors.lastname: Wills
authors.forename: S
authors.initials: S
authors.lastname: Murray
authors.forename: A W
authors.initials: AW
authors.lastname: Gordon
mesh_terms: D000821:Animal Feed; D000818:Animals; D002417:Cattle / Q000378:metabolism* / Q000502:physiology; D004032:Diet / Q000662:veterinary; D005260:Female; D006799:Housing, Animal; D008697:Methane / Q000032:analysis* / Q000096:biosynthesis; D013459:Sulfur Hexafluoride
chemical_list: D008697:Methane; D013459:Sulfur Hexafluoride