Studies on pathology and diagnosis of ascites syndrome (AS) in poultry-mini review

Ascites syndrome, a metabolic disorder, has become one of the most noticeable non-infectious causes of losses in the broiler industry worldwide, leading to increased mortalities ranging from 5% to 7% or large-scale condemnation of carcasses at slaughter. Ascites presents a significant challenge and has caused substantial economic losses in the global poultry industry. Ascites syndrome (AS), also known as pulmonary hypertension syndrome (PHS), refers to the gradual buildup of fluid in the abdominal cavity, often triggered by inadequate oxygen levels. Incidence rates have been reported ranging from 4% to 10% in different parts of the world, including China, Bangladesh, Iran, and India. The peak occurrence of ascites is typically observed in the 5th or 6th week of the growing period, with the highest mortality occurring after four weeks. Affected chicks exhibit symptoms such as dilated abdomen, rapid respiration, bradycardia, and a pot-bellied appearance, ultimately succumbing to hypoxia. Post-mortem examination of ascitic birds reveals the presence of a significant amount of clear yellow fluid known as ascitic fluid. The heart is markedly enlarged, and hydropericardium and pericardium with adhesions are observed. The lungs exhibit extreme congestion and edema. Microscopic examination of heart tissue from ascitic birds shows myofibril disorientation and degeneration with extensive mitochondrial hyperplasia. In the lungs, parabronchi are significantly dilated, with areas of sub-epithelial fibrosis and higher-than-normal surfactant material. Ascites can be diagnosed based on clinical and post-mortem findings. In acute cases, clinical diagnosis is rare as the animal often dies. Palpation of the abdominal area below the chest muscles to detect moving fluid is a common finding in acute cases. Upon opening the abdominal cavity, a substantial amount of fluid with or without a fibrin clot is usually observed. Fluid accumulation in the pericardium (hydropericardium) leads to rapid death.