The ascites syndrome is a cardiopulmonary condition which affects young just-growing broiler chickens. It is identified by the accumulation of serous fluid in the abdominal cavity and birds die from chronic passive congestion and right ventricular heart failure. Many reports refer to its incidence among broilers maintained at altitudes greater than 3000 m. It is thought that hypoxia caused by decreased partial pressure of atmospheric oxygen (p02 results in a syndrome of cor pulmonale analogous to high mountain disease in cattle and is a major cause of ascites. From the mid 1980's, however, there have been more frequent reports that refer to the occurrence of spontaneous outbreaks of ascites in flocks maintained at moderate altitudes or even at sea level. At sea level, the increased frequency of this syndrome has still to be determined.

Because the pathology of this syndrome is characterised by marked ascites, cardiomyopathy, pulmonary congestion and oedema and hepatopathy, much of this talk will concentrate on morphological changes, both spontaneous and induced, that have been identified in altitude - and sea level-reared broiler chicks. Histo/ultracytochemical techniques have been used to investigate the possible role of tissue oxygen underutilisation in the broiler ascites syndrome at low altitude.