A meta-analysis of environmental factor effects on ammonia emissions from dairy cattle houses

Livestock housing is one of the main sources of ammonia (NH 3 ) emissions from agriculture. Different management and environmental factors are known to affect NH 3 emissions from housing systems. The aim of this study was to quantitatively define the effect of temperature, wind speed, relative humidity, and ventilation rate on NH 3 release rates from dairy cattle housing by conducting a meta-analysis of published scientific results. A literature survey was performed to review studies published before January 2018 that have identified statistical relationships between NH 3 emissions and environmental factors such as air temperature, wind speed, relative humidity, or ventilation rate in dairy cattle housing. Experimental values were related using a mixed model analysis in order to analyse the effect of environmental factors on NH 3 emissions. For this exercise, a total of 19 peer-reviewed papers were considered and 27 different relations between air temperature and NH 3 emissions were used for the analysis. A significant effect of air temperature inside the barn and ventilation rate on NH 3 emissions was observed. Results showed that NH 3 emissions increased linearly with increasing air temperature (oC) inside the barn by 1.47 g [NH 3] cow −1 d −1 when temperature increased by one degree. For ventilation rate, an increase of 100 m 3  h −1 cow −1 led to an increase in NH 3 emissions of 0.007 g [NH 3 ] cow −1 d −1 . The equations obtained in this work might help to provide information on NH 3 barn-related emissions behaviour under these environmental conditions, bearing in mind that other source of emissions such as diet composition and animal performance might be also affected by climate changes.