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

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Livestock housing is one of the main sources of ammonia (NH3) emissions from agriculture. Different management and environmental factors are known to affect NH3 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 NH3 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 NH3 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 NH3 emissions. For this exercise, a total of 19 peer-reviewed papers were considered and 27 different relations between air temperature and NH3 emissions were used for the analysis. A significant effect of air temperature inside the barn and ventilation rate on NH3 emissions was observed. Results showed that NH3 emissions increased linearly with increasing air temperature (oC) inside the barn by 1.47 g [NH3] cow−1 d−1 when temperature increased by one degree. For ventilation rate, an increase of 100 m3 h−1 cow−1 led to an increase in NH3 emissions of 0.007 g [NH3] cow−1 d−1. The equations obtained in this work might help to provide information on NH3 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.