Here’s a publication laying out the state of the science in estimating greenhouse gas emissions from livestock- and poultry-production systems, published by USDA in the summer of 2014.  The report shows how to estimate emission rates and emission fluxes from systems producting the following species:

• Dairy Cattle
• Beef Cattle
• Swine
• Poultry
• Goats
• Americon Bison

Sources and Sinks of Greenhouse Gases from Livestock Systems