The debate about co-existence usually focuses on the situation of neighbouring farms. Organic producers take the position that co-existence affects the whole supply chain. Therefore, this paper compares the maize grain supply chains in Switzerland and Spain in order to identify which factors influence the segregation of genetically modified (GM) maize from non-GM maize, and discusses how organic production copes with the challenge of GM maize. Considerable differences exist between Spain and Switzerland with regard to grain maize as a component of animal feed. In Spain, where GM maize is grown, it is the feed industry that defines standards in the supply chains. Since the trading co-operatives are unable to supply GM-free maize, independent and separate infrastructures have been developed for a GM-free maize supply (e.g. for maize starch). In Switzerland, the retailers define quality standards for suppliers, and these standards exclude the use of GM plants for feed. Therefore, the feed industry has to segregate GM from non-GM feed
