Methane and carbon dioxide ratio in excreted air for quantification of the methane production from ruminants

This technical note presents a simple, fast, reliable and cheap method to estimate the methane (CH4) production from animals by using the CH4 and carbon dioxide (CO2) concentrations in air near the animals combined with an estimation of the total CO2 production from information on intake of metabolizable energy or heat producing units. By using portable equipment to analyse the air in stables or near individual animals it is possible to calculate the proportion of the carbon that is not metabolized to CO2, but excreted as the greenhouse gas CH4. The CH4/CO2 proportion in itself gives useful information and can be seen on the spot when measuring. A more detailed use of the data in combination with feedstuff analysis can be used to estimate the quantitative CH4 production from the animals as the CO2 excretion can be calculated from the intake of metabolizable energy minus the energy in the weight gain or milk produced, as there is close relation between heat production and CO2 excretion. Moreover, data from air analysis in livestock buildings shows a close relation between CO2 production and the amount of heat producing units (HPU) in a stable, which also in this situation makes CO2 a good marker for the quantitative excretion of gases and thereby a marker to be used for the calculation of the quantitative CH4 production from livestock.