As the result of phosphorus being identified as the most harmful pollutant, government regulations introduced in the Netherlands in the 1990s to reduce environmental damage from livestock wastes used phosphorus content as the marker criterion. This subsequently led to reductions in the amounts of phosphorus included in animal feed compounds. Particularly in the case of broiler breeder and broiler grower diets, it was concluded that increased mortality, increased morbidity and other adverse effects on performance were largely the result of insufficient dietary phosphorus. Measures taken have included on-farm addition of supplementary phosphorus and calcium and adjustments by the feed industry. In general, levels of performance have now been restored. However, it is concluded that more research on optimum phosphorus levels is desirable, particularly as producers have to bear the cost of the residual phosphorus in the poultry manure produced.