Overview

Ascites syndrome (AS), also known pulmonary hypertension syndrome or water belly, is caused by right ventricular failure (RVF). It is a significant economic burden to the global poultry industry due to reduced growth performance, increased mortality and condemnations at slaughter.

This non-infectious condition is most common in male broiler chickens, but also occurs in chickens, turkeys, guinea fowl and ducks.

This syndrome became a major issue in the 1990s and has coincided with continuing genetic and nutritional improvement in feed efficiency and rate of growth in the broiler industry.

To reduce the impact of AS on birds’ health and performance, poultry producers need to understand the underlying causes and implement appropriate measures.

Causes and predisposing factors of ascites

AS in broiler chickens is a condition with many causes influenced by genetic, nutritional and environmental factors.

Rapid growth

The high metabolic rate of modern broiler chickens creates high oxygen demand, which puts strain on the heart muscle.

Genetics

Certain breeds exhibit greater susceptibility to AS due to genetic predisposition. Research suggests only a few major genes are involved with moderate to high heritability (Wideman et al., 2012).

Environmental factors

Environmental factors include:

  • cold stress - increases oxygen demand for thermoregulation
  • poor ventilation - impairs oxygen exchange due to high levels of ammonia, carbon dioxide and carbon monoxide accumulation
  • high stocking density - contributes to heat stress and reduced air quality
  • lung infections - further compromise respiratory function
  • sodium intake toxicity - increases blood volume and viscosity

Clinical signs

Mortality from AS is greatest in birds at the end of their rearing period. Occasionally, young broilers will develop AS, particularly if they are raised in poor nutritional and environmental conditions.

Clinical signs include:

  • distended abdomen (water-belly)
  • difficulty breathing (open-beak breathing)
  • cyanosis (bluish discoloration of skin and mucous membranes) or red abdominal skin
  • lethargy, dullness and/or depression
  • reduced exercise tolerance
  • sudden death

Post-mortem examination

Post-mortem findings include:

  • fluid accumulation in the abdomen
  • enlarged and congested liver
  • enlarged and thickened right ventricle of the heart with fluid in the sac
  • congested and edematous lungs

Prevention

A combination of improving genetics, nutrition and environmental conditions may contribute to minimizing the incidence of AS.

Genetics

To improve genetics, select breeds with lower susceptibility to AS.

Nutrition

To improve nutrition:

  • reduce feed intake to slow the growth after 30 to 35 days
  • transition early to grower-finished diets
  • use a skip-a-day feed regime
  • use a mash form instead of pellet diet
  • monitor sodium intake in feed and water

Environment

To improve their environment:

  • maintain proper ventilation
  • decrease daylight hours in the barn
  • ensure adequate temperature and humidity