Here is an interesting and slightly bizarre article discussing research conducted to review the carbon footprint left from the production of dairy. Apparently, the dairy industry makes a large enough impact on rising levels of greenhouse gases, that it has set a goal of reducing emissions by 25 percent by 2020. Of the processes analyzed, the biggest contributors were feed production, methane gas from the animal itself (farts, flatulence, etc.), and manure management.
I had no idea that cows were such large contributors to global warming!