International debate continues about the potential effects of global warming and agriculture's role in creating and mitigating it. Needed in this discussion are detailed analyses of production systems and the factors within systems that may reduce emissions with global warming potential. I created a life cycle assessment computer model to quantify emissions from three dairy systems in Iowa--grazing, conventional, and conventional/grazing. These were modeled using system expansion methodology and SimaPro 7.1 software. Results suggest that there is a difference in emissions between system types, but more potential for reduction exists within each system than the difference between the systems.

Previously unanalyzed characteristics of dairy systems, such as interval between calving and culling rate differ between systems and have considerable effects on the net emissions. Using the COWPOLL mechanistic enteric fermentation estimation method was key in accurately differentiating emissions from grass-fed and concentrate-fed animals. Sensitivity analysis on each individual characteristic of the dairy systems leads us to conclusions of how emissions may be reduced, which differs between the dairy systems. Life cycle assessments such as this one may help lower emissions from dairy systems by targeting individual characteristics within dairy systems that can effectively reduce greenhouse gas emissions.