Ascites in broiler chickens: exogenous and endogenous structural and functional causal factors

Broiler chickens and laying hens are intensively selected for productive traits. The management of these highly productive animals must be optimal to allow their full genetic potential to be expressed. If this is not done, inefficient production and several metabolic diseases become apparent. The causes of the latter are multifactorial but diet and, particularly, interactions between diet, other environmental and genetic factors play an important role. An imbalance between oxygen supply and the oxygen required to sustain rapid growth rates and high food efficiencies causes ascites in broiler chickens. It is clear that several nutritional factors, the amount of food given, its physical form and the composition of the diet have a major impact on the occurrence of ascites and sudden death syndrome in broiler chickens. Furthermore, the possible involvement of structural endogenous factors such as proportional changes in the respiratory and cardiovascular systems, shifts in the glycolytic:oxidative muscle metabolism ratio, and structural changes within the lung capillary system cannot be excluded. In addition, functional causal factors, such as the hypothyroid state associated with decreased maintenance metabolism as a result of the selection for fast growth rate and improved food efficiency, are likely to be involved. Both structural and functional causal mechanisms may already be initiated during the embryonic stage.