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

Abstract This technical note presents a simple, fast, reliable and cheap method to estimate the methane (CH 4 ) production from animals by using the CH 4 and carbon dioxide (CO 2 ) concentrations in air near the animals combined with an estimation of the total CO 2 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 CO 2 , but excreted as the greenhouse gas CH 4 . The CH 4 /CO 2 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 CH 4 production from the animals as the CO 2 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 CO 2 excretion. Moreover, data from air analysis in livestock buildings shows a close relation between CO 2 production and the amount of heat producing units (HPU) in a stable, which also in this situation makes CO 2 a good marker for the quantitative excretion of gases and thereby a marker to be used for the calculation of the quantitative CH 4 production from livestock.