During the genetic selection process of the past few decades, changes have occurred in the way some genotypes have responded to the environment and to other conditions. For example, some genetic lines have responded better to complete confinement but poorly to outdoor conditions. Some sows perform more favorably to early weaning but perform poorly to later weaning. One trait that has changed and also seems to vary between genetic lines is the pig's feed intake response. Some of the leaner genotypes have demonstrated a lower feed consumption and a lower daily gain than other genetic crosses. Because of potential genetic differences for muscle deposition between genotypes, the efficiency of feed utilization is also quite different. Those genotypes with a higher potential for lean tissue growth, but which may also have a lower feed intake, must have their diets formulated differently than pigs of other genetic and appetite characteristics. Consequently, seedstock producers, particularly those producing synthetic lines, should provide the commercial swine producer with expected feed intakes, performance responses, carcass information, sow longevity, and other herd characteristics. Attempts to evaluate nutrient requirements for specific genotypes is difficult without this information.