During the past half century, genetic selection, heterosis, changes in husbandry, improved nutrition, and control of diseases and parasites have contributed to the escalating growth rate of meat-type poultry. In the 1940's, broilers required 12 weeks to reach a market weight of 4.4 pounds; today they achieve this weight in 6 weeks, and the reduction by the industry of 1 day per year to achieve this weight continues unabated. Comparable changes have occurred in turkey and waterfowl production. The result is greatly improved efficiency of feed utilization because of reduced maintenance.
Several health and welfare problems seen predominantly in meat-type birds are related to rapid growth rate. A correlated response to the selection of turkeys for increased body weight and a broad breast is the development of deep muscle myopathy (atrophy of the inferior pectoralis muscle) caused by an inadequate blood supply to the tissues. Both turkeys and meat chickens exhibit skeletal disorders, particularly in the bones of the pelvic limb (femur, patella, tibia, metatarsus) and their associated tendons. These disorders are not necessarily associated with body weight or conformation, but instead with the differential growth of body parts, particularly accelerated growth of muscle that is not commensurate with skeletal development. Skeletal abnormalities can be further exacerbated by the resulting motor impediments. The lack of synchronous growth among body components in broilers, including the heart and lungs, can contribute to pulmonary hypertension causing excess fluids in the body (ascites). An additional problem is "sudden death syndrome," the cause of which is unknown.
These health problems are of great concern to the poultry industry, and considerable research is being conducted on the negative aspects associated with rapid growth in today's broilers. Relationships are complex, and in some cases neither genetic nor non-genetic solutions are readily available. Some alleviation, however, may be feasible by moderating growth during certain periods in the bird's life.
