Ruminants are recognized sources of greenhouse gas (GHG) emissions. The objective of this paper was to estimate the carbon footprint of dairy and beef farms in different production systems in Spain. Component models for predicting all important sources of CH4, N₂O, and CO₂ from primary and secondary sources in dairy and beef production were estimated with the Integrated Farm System Model (IFSM) and reported in CO₂ equivalent (eCO₂/kg of energy-corrected milk (ECM) or kg body weight (BW)). The IFSM and Cornell Net Carbohydrate and Protein System (CNCPS) were used to evaluate dairy and beef farms in Spain for GHG emissions and diet evaluation on methane production, respectively. Three dairy farms from each of 3 regions were selected: Mediterranean (Catalonia, Valencia and Murcia), Cantabric area (Galicia, Asturias and Cantabria) and Central zone (Castilla-La Mancha, Castilla-Leon and Madrid). The average carbon footprint (kg eCO₂/kg of ECM) of all dairy farms was 0.83, with the Mediterranean farms being highest (P < 0.01); 0.98) compared with the Central Zone (0.84) and the Cantabric area (0.67). Two extreme farms were selected for further simulations: the first one had the highest carbon footprint and non-enteric methane, while the second had the lowest carbon footprint and the highest enteric methane. These farms were simulated by the IFSM model using different management change scenarios (higher productivity, manure type collection, bedding type, anaerobic digester and storage type of manure) and dietary changes (modification of the ratio forage:concentrate, improved forages quality, inclusion of fat, use of ionophore). Management changes reduced methane emission up to 30% while dietary change reduced it up to 5%. Two beef farms fed 90:10 concentrate:straw and one fed with corn silage were used to simulate GHG emissions using the same models. The carbon footprint (eCO₂/kg BW) was 6.98 in beef fed corn silage and 6.90 in beef fed without corn silage. Management strategies provided a greater potential to reduce methane emissions compared with dietary scenarios changes.