Whole-farm management is necessary to decrease nitrogen lossesin animal production. If steps are taken to reduce loss in onecomponent of the farm, the nitrogen saved will likely be lostelsewhere if all components are not equally well managed. Managementmust focus on improving the nitrogen use efficiency of the animalsto reduce nitrogen excretion, retaining that nitrogen in themanure until it is incorporated into the soil, and applyingthe appropriate amount of manure in a timely manner to enhancecrop uptake. Management of all the factors involved in the nitrogencycle of the farm is complex. Whole-farm research on nitrogenmanagement is needed, but such research is difficult and expensive.Computer simulation and other farm models provide research toolsthat integrate farm components to assess and compare long-termeffects of production systems. These models can provide helpwith strategic farm planning and tactical operations to reduceadverse environmental effects, while maintaining or improvingfarm profit.