|Title||Nutritional and environmental effects on ammonia emissions from dairy cattle housing : A meta-analysis|
|Author(s)||Bougouin, Adeline; Leytem, April; Dijkstra, Jan; Dungan, Robert S.; Kebreab, Ermias|
|Source||Journal of Environmental Quality 45 (2016)4. - ISSN 0047-2425 - p. 1123 - 1132.|
|Publication type||Refereed Article in a scientific journal|
Nitrogen excreted in dairy manure can be potentially transformed and emitted as NH3, which can create livestock and human respiratory problems and be an indirect source of N2O. The objectives of this study were to: (i) investigate environmental factors influencing NH3 emissions from dairy housing; and (ii) identify key explanatory variables in the NH3 emissions prediction from dairy housing using a meta-analytical approach. Data from 25 studies were used for the preliminary analysis, and data from 10 studies reporting 87 treatment means were used for the meta-analysis. Season and flooring type significantly affected NH3 emissions. For nutritional effect analysis, the between-study variability (heterogeneity) of mean NH3 emission was estimated using random-effect models and had a significant effect (P <0.01). Therefore, random-effect models were extended to mixedeffect models to explain heterogeneity regarding the available dietary and animal variables. The final mixed-effect model included milk yield, dietary crude protein, and dry matter intake separately, explaining 45.5% of NH3 emissions heterogeneity. A unit increase in milk yield (kg d-1) resulted in a 4.9 g cow-1 d-1 reduction in NH3 emissions, and a unit increase in dietary crude protein content (%) and dry matter intake (kg d-1) resulted in 10.2 and 16.3 g cow-1 d-1 increases in NH3 emissions, respectively, in the scope of this study. These results can be further used to help identify mitigation strategies to reduce NH3 emissions from dairy housing by developing predictive models that could determine variables with strong association with NH3 emissions.