Endogenous and environmental factors interactions that contribute to the development of ascites in broiler chickens: a review

The increasing susceptibility of broiler chickens to ascites syndrome has coincided with a continuing genetic and nutritional improvement in their feed efficiency and growth rate. Ascites is multifactorial and interactions between environmental and endogenous factors play a particularly important role. The selection of fast growing broilers for high feed efficiency, which is characterized by hypothyroidism, can consequently lead to a mismatch between oxygen (O2) delivery and O2 demands. This results in anoxia, hypoxemia and hypoxia. Such selection processes have also resulted in the development of birds with changed anatomical, physiological, metabolic and hematological parameters, including thyroid hormone activity, partial pressure of O2 and carbon dioxide in venous blood, cardiac ?-adrenergic receptors, and hematocrit levels that coincide with susceptibility to ascites in broiler chickens. Observations to date indicate that the structural or endocrine changes that are often linked with ascites susceptibility may be influenced during the early stages of development, embryogenesis and incubation. In this review, particular attention will be paid to the interactions between endogenous and exogenous factors as predisposing factors for the development of ascites syndrome. Additionally, preventive management procedures will be highlighted, such as different lighting schedules, feed restriction protocols and the supplementation of feed with antioxidants, which reduce the incidence of ascites by altering the metabolic load of broiler chickens amongst other factors.