The poultry meat industry, in continual pursuit of improved efficiency, has demanded rapid growth rate. Primary breeding companies have responded to industry pressure and growth rate has increased in an almost linear fashion. Despite the obvious advantages to industry profitability, it can be argued that increased growth has placed more emphasis on the demand tissues of growth than those systems or organs that supply the substrates for rapid growth and/or are essential to support the increase in body mass. One of the consequences is that modern broilers are not as adaptable to their environments as their predecessors were. Rapid growth has also produced problems not seen in slower growing birds. Skeletal and cardiovascular disease (sudden death syndrome (SDS), ascites) are examples of growth related problems. Although it can not be said that rapid growth automatically will result in these problems, there is no doubt that the!re is a relationship.