Methane emissions from ruminants in integrated crop-livestock systems

is a powerful greenhouse gas, with a global warming poten-tial of 25 (Eckard et al. 2010) and represents a significant loss of dietary energy (2–12% of gross ener-gy of feeds; Patra 2012) in the ruminant production system. Despite greenhouse gas (GHG) emissions hav-ing become an increasingly important topic worldwide, there is still high variability in the estimated values of these emissions, mainly those attributable to livestock (range 8–51%; Herrero et al. 2011). This variability creates confusion among researchers, policy makers and the public, particularly in tropical/subtropical regions. Therefore, using rigorous and internationally accepted protocols, a Brazilian national project was established to contribute to improving estimates of GHG emissions attributable to livestock in Brazilian ruminant production systems. Moreover, enteric CH