Rapid growth problems: ascites and skeletal deformities in broilers.

Over the last 40 yr, genetic selection for rapid growth and improved feed efficiency has been very effective in meat-type poultry. Combined with changes in the feed that have increased both the nutritional and physical density to encourage a high nutrient intake, growth rate has more than doubled. The effect of genetic selection for high muscle to bone ratio and high calorie intake of a ration that supplies all nutritional requirements causes significant mortality from cardiovascular disease. In the chicken, sudden death syndrome (flip-over) and pulmonary hypertension syndrome resulting in ascites are the most important. Ruptured aorta, spontaneous turkey cardiomyopathy (round heart), and cardiomyopathy causing sudden death produce high mortality in turkeys. Rapid growth induced by high nutrient intake alone can cause severe lameness, bone defects, and deformity, as these problems are seen in animals that have not been selected for rapid growth: dogs, horses, pigs, ratites and wild birds kept in zoologic gardens. In meat-type poultry, growth-related disease can be reduced or eliminated by reducing feed intake without affecting final body weight. Rapid growth alone may not be the pathogenic mechanism that results in cardiovascular or musculoskeletal defects. Metabolic imbalance induced by high nutrient intake may cause some of the conditions. These metabolic problems might be corrected without reducing growth rate.