Methane, nitrous oxide and carbon dioxide emissions from ruminant livestock production systems

System inputs with greenhouse gas (GHG) implications were summarized for typical U.S. beef production systems and for representative U.S. and N.Z. dairy systems. The GHG emissions are expressed in carbon dioxide equivalents (CO(2)eq) and related to livestock system product output. The U.S. beef systems are estimated to produce from 13 to 16 kg of CO(2)eq per kg of live weight sold and the dairy systems 1.3 kg Of CO(2)eq/kg of milk while the pasture based N.Z. dairies produced 1.6 kg/kg milk. Relative source strengths varied. Nitrous oxide was the largest CO(2)eq source of beef system emissions, 52%, with 36 and 12% from methane (CH(4)) and carbon dioxide (CO(2)). The amount of methane per wt sold was quite uniform across location in the U.S., while nitrous oxide was variable ranging from 7 in WI to 9 kg CO(2)eq/kg sold in TX Methane was the largest CO(2)eq source from CA dairies, while nitrous oxide (N(2)O) was the largest in N.Z. dairies. High CH(4) in CA was due to extensive use of anaerobic lagoon disposal of manure while excess N content and flux on N.Z. pastures caused higher relative N(2)O emissions. Utilization of best management practices and manure amendments to sequester carbon in the crop and forage land of ruminant livestock production systems have modest potential to offset their GHG emissions.