INTRODUCTION
Decreasing the potential of global warming by reducing emissions of greenhouse gases is a social and environmental priority. Methane (CH4) is a potent greenhouse gas that is produced in the rumen by highly specialized bacteria, and a recent review (Hristov et al., 2013) reports wide variability for CH4 yield: 16 to 26 g/kg of DMI. The variability in CH4yield depends on several factors, and the chemical composition of TMR fed to cattle strongly affects emissions.