Validation of a short-term methane measurement using portable static chambers to estimate daily methane production in sheep

Abstract

There is increasing demand for technologies to measure CH4 production (DMP) of ruminant livestock in inventory and mitigation research. Studies of genetic variation among animals in DMP require these emissions to be measured on thousands of animals which cannot be managed using traditional chamber studies. However, short-term emission measures have been reported to correlate well with DMP. Our study was conducted to determine the usefulness of 1 and 2 h emission measures using chambers in predicting DMP. In our first experiment, Merino sheep (n = 13) were measured for DMP over 22 h using open circuit chambers. On two subsequent days, after overnight fasts, sheep were offered feed for 1 h before return to the chambers for 2 h and their CH4 production determined. DMP estimated from 22 h measurements correlated moderately well with 2 h emission measures (r² of 0.42-0.48) and 1 h measures (r² of 0.39-0.43). In our second experiment, portable static chambers were designed for 1 and 2 h CH4 emission measurements. The portable static chambers retained 98-99% of an injected tracer gas after 2 h showing that gas leakage from the chamber was very low. With a sheep inside a portable static chamber, CO₂ concentration reached 2.2 x 103 ppmv after 2 h, but sheep showed no discomfort and the partial pressure of O₂ in their blood remained above 97% (i.e., safe for animal health). Our third experiment was to validate use of short-term emission measures from portable static chambers as predictors of DMP. Crossbred Dorset and Border Leicester and Merino ewes (n = 40, LW 54 ± 10.9 kg) were measured for three 22 h sessions in open circuit chambers, after which they were measured for 1 h in portable static chambers. Open circuit chamber measurements had high repeatability (i.e., 0.88) and, excluding one sheep with inconsistent eating patterns, the correlation (r) between 1 h portable static chamber measurements and average emissions in the open circuit chambers was 0.71. We conclude that 1 and 2 h measures of CH4 output in portable static chambers are useful for determining genetic differences in CH4 production in groups of ruminants.