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Nutritional and Environmental Effects on Ammonia Emissions from Dairy Cattle Housing: A Meta-Analysis
- Bougouin, Adeline, Leytem, April, Dijkstra, Jan, Dungan, Robert S., Kebreab, Ermias
- Journal of environmental quality 2016 v.45 no.4 pp. 1123-1132
- United States Environmental Protection Agency, ammonia, barns, cattle housing, crude protein, dairy cows, data analysis, dry matter accumulation, dry matter intake, emissions, environmental factors, excretion, humans, inventories, manure handling, meta-analysis, milk consumption, milk yield, models, nitrogen, nitrous oxide, odors, prediction, urine, United States
- 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 mixed-effect 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.