“Development and possible applications of long term slow intake breath samplers in identifying methane phenotype of ruminants.”

GERE J. I.; GRATTON R.; JULIARENA P.; WILLIAMS K. E.

Wellington

Workshop; Livestock Breedings from Greehouse Gas Outcomes.; 2009

Livestock Emissions & Abatement Research Network

As the inter-animal and inter-day variance of methane emission by ruminants are high, experiments should involve many heads whose emission should be monitored for a long time, in some cases months, to allow for adaptation to new conditions. Therefore, monitoring techniques should be cheap and logistically simple. Besides, animal stress should be minimized during measurements. The best approach so far available to measure methane emission by ruminants is probably the SF6 tracer technique. Usually, 1.5 L PVC canisters have been used and the sampling time defined as the time to rise to 500 mbar the air pressure in initially void canisters, was 24 hours or less. Air inflow is easily restricted to the needed value thanks to the hydraulic impedance of moderately expensive stretch (length 1 m) of thin capillary tubes. However, even this valuable technique is logistically demanding and expensive when applied to many heads during long times. Therefore, to substantially reduce the number of samples and the corresponding analysis in long experiments, we developed a modified version with raised to 5 days while the canister volume is kept small (0.5 L). Likewise sampling sets may easily be adjusted for 15 days, but we do not use so far these latest ones on animals. Apart from logistical simplification and cost reduction, we expect that averaging effects due to the extension of to many days with canisters of 0.5 L needs of air inflow regulators (IR)with conductances of the order of 10-4 mbar.L/s for a pressure difference of 1 bar. As this would require very long and expensive capillary tubes, it is preferable to replace them by other kind of flow controllers.Therefore, we develop geometric leaks, based on cheap commercially available components. The same components may be adjusted within a wide conductance interval. Basically, we assemble the IR by pressing a steel bearing-ball (diameter 8 mm) against the border of the cylindric central hole of a standard tubery union by means of a threaded plug. Both the union and the plug are brass made and all elements are commercially available at low cost. As the stability of the IR in field experiments was satisfactory we conclude that the extension of sampling times in the SF6 tracer technique is simple and not expensive. This conclusion may be important in the concern of the identification of ruminant methane emission phenotypes characterized by low methane emission.