The GreenFeed system for measurement of enteric methane emission from cattle

Methane measurements from cattle would benefit from an improved capability to measure a larger number of animals, with a lower requirement for specialist technical knowledge, and minimal human interference. The GreenFeed (GF) system (C-Lock Inc., Rapid City, SD, USA) estimates daily methane production (DMP, g/day) by measuring gas concentrations and airflow over 3-7 min from cattle when they visit a GF unit. Although few data are collected per animal per day, over many days of GF visitation estimates of DMP can be established. Published GF estimates of DMP are in agreement with DMP measured by respiration chambers, but there are inconsistencies in comparisons based on estimates using the sulfur hexafluoride tracer method. Circadian patterns of methane emission from cattle suggest spot-sampling of emissions by GF should be distributed over 24 h, or weighted to avoid bias associated with clustering of GF visits at specific times. Up to half of cattle grazing temperate pastures choose not to use GF on a daily basis, so consideration must be given to the number of animals and duration of sampling as well as the proportion and representation of animals using GF for estimating DMP, especially for ranking individuals. All systems for determining DMP from animals constrain the data in some way, and the suitability of the GF system will be affected by the experimental objectives and design. For example, compared with the respiration chamber and sulfur hexafluoride tracer techniques, it takes more time and animals to undertake a treatment comparison of DMP using GF due to higher within-day and within-animal variance, especially if some avoid GF or do not visit each day.