Extending the Collection Duration of Breath Samples for Enteric Methane Emission Estimation Using the SF(6) Tracer Technique

SIMPLE SUMMARY: Extended sample collection for the SF(6) tracer technique is desirable for extensive grazing systems. Breath samples from eight cows were collected while lucerne silage was fed to achieve fixed intakes among the cows. Samples were collected over a 10-day period, using either apparatuses used in New Zealand (NZL) or Argentina (ARG), and either daily, over two consecutive 5-day periods or over a 10-day period (in duplicate). The NZL system had a greater sampling success and more consistent CH(4) emission estimates than the ARG system, with no differences in mean emissions among sample collection periods. This study showed that extended sample collection is feasible, but definitive evaluation under grazing situation is required before a decision on recommendation can be made. ABSTRACT: The daily sample collection protocol of the sulphur hexafluoride (SF(6)) tracer technique for the estimation of methane (CH(4)) emissions from ruminants may not be practical under extensive grazing systems. Here, under controlled conditions, we evaluated extended periods of sampling as an alternative to daily sample collections. Eight rumen-fistulated cows were housed and fed lucerne silage to achieve common daily feed intakes of 6.4 kg dry matter per cow. Following SF(6) permeation tube dosing, eight sampling lines were fitted to the breath collection harness, so that a common gas mix was available to each line. Half of the lines collected samples into PVC yokes using a modified capillary system as commonly used in New Zealand (NZL), and half collected samples into stainless steel cylinders using a ball-bearing flow restrictor as used in Argentina (ARG), all within a 10-day time frame, either daily, across two consecutive 5-day periods or across one 10-day period (in duplicate). The NZL system had greater sampling success (97.3 vs. 79.5%) and yielded more consistent CH(4) emission estimates than the ARG system. Emission estimates from NZL daily, NZL 5-day and NZL 10-day samplings were 114, 110 and 111 g d(−1), respectively. Extended sample collection protocol may be feasible, but definitive evaluation of this alternative as well as sample collection systems is required under grazing situations before a decision on recommendation can be made.