In contrast to ammonia few data about the emissions of CH4, N2O and CO2 from animal houses are yet available. To be reliable, such data should derive from investigations meeting the following minimum requirements: (1) continuous measurement of ventilation rates and gas concentrations; (2) long-term experiments, to cover diurnal and seasonal effects; (3) use of extremely exact measuring equipment. A literature review has shown that reliable data about CH4 emissions are basically only available for cattle housing systems. Data about N2O emissions from animal houses are lacking, because of the difficulties in measuring very low N2O concentrations. However, the results of existing investigations are not comparable and most of them do not meet the minimum requirements mentioned above. Our own experiments have been carried out for dairy cows in loose housing with natural ventilation. The amount of CH4 originating from cows' digestion is about 223 g per livestock unit (1 LU = 500 kg live-weight) per day and varies between 200 and 250 g per LU per day. It mainly depends on the feed intake, which is positively related to animal size, growth rate and production. There is practically no influence of outside conditions on the emission rate. N2O was emitted at about 1.6 g per LU per day.
