The conversion to OF for three specialized suckler cattle farming systems was simulated by coupling an economic optimization model (“Opt'INRA”) with a model assessing on‐renewable energy (NRE) consumption and greenhouse gas (GHG) emissions (“PLANETE”). Based on average prices over 2004‐2008, and after adaptation of the production system, we analyzed the productive, environmental and economic impacts of the conversion process. The ban on chemical fertilisers entails a drop in farm area productivity. For these specialized farms, meat production decreased by 19 to 37% depending on the initial level of intensification. The reduced use of inputs results in a 23 to 45% drop in non‐renewable energy consumption per hectare and a 5 to 16% drop per ton of live weight produced. Due to its methane production, the cow is the biggest driver of GHG emissions. The shift to OF does significantly not affect gross GHG emissions per ton of live weight produced, but, taking into account carbon sequestration in grasslands, net GHG emissions could be lower for OF systems. The lower productivity per hectare (less animals reared per ha) allows a 26 to 34% reduction in net GHG emissions per hectare of farm area. Economically, the drop in productivity is not compensated by the gain in the meat selling price (+5 to +10%), gross farm product drops by 9 to 16%, and the lower use of inputs entails a strong drop in operational costs: ‐9 to ‐52%. Farm income falls more than 20% (‐7 to ‐46%).