Quantifying daily methane production of beef cattle from multiple short-term measures using the GreenFeed system

Abstract

On-farm CH₄ emissions have been identified as the largest contributors to the carbon footprint of livestock production systems. A requirement to quantify on-farm mitigation under commercial production conditions and a desire to establish the phenotype of thousands of ruminants for breeding programs, has fueled the development of techniques to estimate daily methane production (DMP) from short-term measures of methane concentration or methane flux.The accuracy, precision and applicability of these methods has been largely untested and forms the susbtance of this thesis. In assessing the accuracy of short-term emissions measures to estimate DMP, a high level of concordance was observed between DMP measured over 24h in a respiration chamber (RC) and estimated from multiple short-term measurement estimates using the GreenFeed Emission Monitoring system (GEM). Three independent experiments comparing DMP confirmed that estimates between methods differ by 5% to 8% (P>0.05). This implies that multiple short-term measures of emission rates are complementary to and consistent with respiration chamber-derived measures, providing capability to measure a greater number of animals, potentially in their production environment over extended periods of time. Methane yields (MY; g CH₄/kg DMI) were also derived based on multiple short-term emission measures, with results consistently within 10% of those calculated based on 24h RC data. The overall MY of animals consuming roughages was 21.8g CH₄/kg DMI using GEM data, in keeping with the 22.3g CH₄/kg DMI average in the literature. That implies that GEM units can not only accurately estimate DMP of cattle but also support accurate MY estimates that can be used in quantifying livestock emissions for national greenhouse inventory calculations.