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Factors responsible for methane emission from cattle manure representing diverse climates, systems and functions of cattle production are presented. These factors were obtained by means of an experimental methodology developed for this project. It was considered that the temperature, moisture, handling of manure and the animals' feed ration affect methane production. Drying conditions and fermentation of manure in cool, temperate and warm climates were simulated in the laboratory. Cattle manure was obtained from animals in intensive, semi-intensive and extensive production systems; for dairy, non-dairy and double purpose cattle production functions. Also handling of manure in dry lot, pasture and solid storage was considered. Results suggest that the dominant factor in methane emissions is the feed ration, followed by fermentation temperature and the excreta moisture content. The emission factors obtained in this work are at least a factor of five smaller than those proposed in the revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories for countries like Mexico.