Universidade Estadual de Maringa 1 article published in JoVE Environment The Use of an Automated System (GreenFeed) to Monitor Enteric Methane and Carbon Dioxide Emissions from Ruminant Animals Alexander N. Hristov1, Joonpyo Oh1, Fabio Giallongo1, Tyler Frederick1, Holley Weeks1, Patrick R. Zimmerman2, Michael T. Harper1, Rada A. Hristova3, R. Scott Zimmerman2, Antonio F. Branco4 1Department of Animal Science, Pennsylvania State University, 2C-Lock, Inc. Rapid City, SD, 3Color Productions, State College, PA, 4Departamento de Zootecnia, Universidade Estadual de Maringá Accuracy and precision of the techniques used to measure methane emissions from ruminant animals are critically important for the success of greenhouse gas mitigation efforts. This manuscript describes the principles and operation of an automated system to monitor methane and carbon dioxide mass fluxes from the breath of ruminant animals.