Enteric methane concentrations from Boran steers determined with a laser methane detector under open-pen conditions and in the respiration chamber

The Laser Methane Detector (LMD) has been proposed as a means of measuring methane (CH 4 ) emissions from ruminants in their natural rearing environment and ranking different diets and individual animals based on their CH 4 emission potential. The present study aimed to test the use of the LMD for ranking diets, animals, and periods of the day in a typical sub-Saharan African setting. The study involved 18 Boran steers, fed three different forages (Brachiaria, Napier, and Rhodes grass), with CH 4 emissions measured on the first day with the gold standard respiration chamber and on the subsequent day with the LMD in an open pen during 22 hours per day. Following a series of data correction steps, the mean LMD CH 4 concentrations were found to be lower than the mean chamber CH 4 concentrations, with a low overall correlation between the two (r s =0.29). Neither chamber CH 4 nor LMD CH 4 were influenced by forage type. Both approaches recorded highest mean CH 4 concentrations directly after feeding and lowest at night. Although the results demonstrate the ability of the LMD to capture diurnal CH 4 emission patterns and forage-related differences in CH 4 emissions, the ranking of individual animals’ CH 4 emission deviated from the chamber rankings. This was partly due to different feeding schedules between the chamber and the open pen, but also to abiotic environmental factors that affected the LMD readings and could not be fully removed through systematic data cleaning procedures.