Nutritional and environmental effects on ammonia emissions from dairy cattle housing: A meta-analysis

Authors: BOUGOUIN, ADELINE - University Of California; Leytem, April; DIJKSTRA, JAN - Wageningen University; Dungan, Robert - Rob; KEBREAB, ERMIAS - University Of California

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2016
Publication Date: 6/29/2016
Publication URL: http://handle.nal.usda.gov/10113/62935
Citation: Bougouin, A., Leytem, A.B., Dijkstra, J., Dungan, R.S., Kebreab, E. 2016. Nutritional and environmental effects on ammonia emissions from dairy cattle housing: A meta-analysis. Journal of Environmental Quality. 45:1123-1132.

Interpretive Summary: Ammonia emissions from livestock production represent 54% of total ammonia emissions in the US. This release of reactive nitrogen contributes to regional air, water, and environmental quality concerns. In addition, ammonia is now being regulated under the Clean Air Act as a precursor to fine particulate matter formation. Nitrogen utilization in dairy cattle is relatively inefficient with 50 to 80% of nitrogen consumed being excreted into the environment, a portion of which is lost as ammonia to the atmosphere. In this study we used a meta-analytical approach to investigate the environmental factors and measurement methods that influence ammonia emissions from dairy housing and identify key explanatory variables in the prediction of ammonia emissions. 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. For nutritional effect analysis, the between-study variability (heterogeneity) of the mean 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. Available dietary and animal variables were included as fixed effects in the mixed-effect models. Results of the analysis indicated that open-lot housing systems had much greater ammonia emissions (145 g/cow/day) compared to naturally or mechanically ventilated barns (6 to 48 g/cow/day). Dairy barns with solid floors had greater emissions (52 g/cow/da) than barns with slatted floors (32 g/cow/day) that allow urine and feces separation. Measurement method also had an impact on measured emission rates with the inverse dispersion method having greater emission rates than either a carbon dioxide balance or tracer method. Ammonia emissions varied by season with the greatest emissions occurring in the summer when temperatures were warmer (83 g/cow/day), with peak winter and fall emissions accounting for 55 to 60% of peak summer emissions. When compared to the US Environmental Protection Agency emission factors, it was found that the USEPA emission factors were lower than those in this study for the ‘scrape dairy barn’ and ‘open-lot’ housing systems, similar for ‘flush dairy barn’, and were higher for ‘deep pit dairy barn’. This suggests that USEPA may need to revise ammonia emission factors based on current published studies of emissions from production facilities. A unit increase in milk yield (kg/d) resulted in 4.9 g cow/d reduction in ammonia emissions, and a unit increase in diet crude protein content (%) and dry matter intake (kg/d) resulted in 10.2 and 16.3 g cow/d increase in ammonia emissions, respectively. Examining results from several studies showed that the NH3 emission is driven by several factors including housing system, season, and diet. Mechanically ventilated barns had the lowest NH3 emissions compared to other housing systems, and pack and pit manure handling had lower NH3 emissions compared with flush and stacked manure handling. Milk yield, DMI and CP content significantly affected NH3 emissions, explaining 45.5% of the heterogeneity. Dietary CP content and DMI positively affected the NH3 emission, whereas milk yield had a negative relationship with NH3 emission. Data from this study can be further used to develop prediction equations for NH3 emission from dairy cattle housing. It could also help to create mitigation strategies to reduce NH3 emissions from dairy cows.

Technical Abstract: Nitrogen (N) excreted in urine by dairy cows can be potentially transformed to ammonia (NH3) and emitted to the atmosphere. Dairy production contributes to NH3 emission, which can create human respiratory problems and odor issues, reduces manure quality, and is an indirect source of nitrous oxide (N2O). The objective of this study was to (i) investigate environmental factors and measurement method that influence NH3 from dairy housing, and (ii) identify key explanatory variables in the prediction of NH3 emissions from dairy barns 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, flooring type, manure handling and housing type and system significantly affected NH3 emission rates as well as the measurement method used to quantify the NH3 emission. Ammonia emissions rates from open-lot and scrape systems were considerably greater and those from deep pit systems lower compared to U.S. Environmental Protection Agency (USEPA) estimates used in national inventory calculations. For nutritional effect analysis, the between-study variability (heterogeneity) of the mean 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. Available dietary and animal variables were included as fixed effects in the mixed-effect models. The final mixed-effect model included dietary crude protein, milk yield and dry matter intake, explaining 45.5% of the heterogeneity in NH3 emissions. A unit increase in milk yield (kg/d) resulted in 4.9 g cow/d reduction in NH3 emissions, and a unit increase in diet crude protein content (%) and dry matter intake (kg/d) resulted in 10.2 and 16.3 g cow/d increase in NH3 emissions, respectively. Ammonia emissions from dairy barns are driven by several factors including housing system, season and diet. Crude protein content of the diet, dry matter intake and milk production are important animal related factors that significantly affect ammonia emission from dairy facilities.