The GreenFeed system for measurement of enteric methane emissions from cattle

Methane measurements from cattle would benefit from lower costs, larger sample sizes, a lower requirement for specialist equipment, and minimal human interference. The GreenFeed (GF) system (C-Lock Inc., Rapid City, South Dakota, USA) estimates methane emission by measuring gas concentrations and airflow from cattle when they visit a GF unit. Evaluation of GF systems suggest similar overall estimates of daily methane production (DMP) made with GF and respiration chambers (RC), but differences to estimates based on the sulphur hexafluoride (SF6) tracer method. GreenFeed estimates are based on spot-sampling, so that measurements are needed over a longer period to obtain an estimate of DMP compared to continuous sampling with RC (or SF6). Circadian patterns of methane emissions from cattle suggest spot-sampling should be distributed over 24 h or weighted to avoid bias associated with uneven distribution of visits to ensure accurate estimates of DMP. A proportion of grazing cattle do not use GF, so consideration must be given to the number of animals and duration of sampling as well as the number, proportion and representation of animals using GF, especially for ranking purposes. All systems for determining DMP from animals involve compromise, and the suitability of the GF system will be affected by the experimental objectives and design. When used in the correct experimental setting GF is a useful tool for estimating DMP from cattle.