Quantifying enteric methane from ruminants: a critical review of group-based measurement approaches

Enteric methane (CH₄) from ruminants is a significant contributor to agricultural greenhouse gas emissions and represents a energy loss to the animal. Accurate and scalable quantification is therefore essential for mitigation strategies, national inventory refinement, and evaluation of genetic or nutritional interventions. While individual-animal techniques (e.g. respiration chambers, GreenFeed, SF₆ tracer) provide high precision, their application is often constrained under commercial or grazing conditions.

This review critically evaluates group-based approaches that estimate CH₄ emissions at herd-paddock-, or facility-scale, including mass balance, eddy covariance, flux gradient, inverse dispersion modelling, and tracer ratio methods. For each technique, we outline measurement principles, spatial scale, typical deployment scenarios, and dominant sources of uncertainty related to atmospheric variability, source geometry, instrumentation, and model assumptions. We propose minimum reporting standards to improve transparency and comparability across studies and discuss trade-offs between precision, scalability, cost, and logistical complexity. Integration of complementary techniques and greater methodological standardisation will enhance the robustness and policy relevance of herd- and farm-scale methane estimates.