In Brittany, animal concentration is responsible for water pollution. French water policy does not stick to Water Framework Directive, though in northern countries polluter-pay principle stimulated manure markets. We tried to calculate the cost of the Nitrate Directive and simulate the manure markets in Brittany. A linear model minimizes the cost of manure management constrained by the Nitrate Directive. Farms process or export their manure in the short-run and reduce their livestock in the long-run, by 20 to 40 % according to types. Market leads to significant savings compared to no trade or to a regional plan aiming at maintaining livestock production.
