Ascites (Waterbelly) in Meat Chickens

by Alberta Algriculture

What is ascites?

Ascites syndrome is a type of congestive heart failure seen mainly in young rapidly growing meat type chickens. It has become a major concern to the poultry industry around the world and it is extremely common in Alberta poultry flocks.

Ascites is an accumulation of protein rich fluid in the body cavity. Because of the high protein level, there may be clots of yellow, jelly-like material.

In birds, the right side of the heart is thin walled and the valve on this side consists of a flap pushed against the wall of the heart. As well, lungs of birds are different from those of animals. Bird lungs have very little ability to expand and the blood capillaries in the lungs are not able to handle increased blood flow or blood pressure.

When the right heart encounters increased blood pressure in the arteries of the lungs, it responds to increased workload, as other muscles do, by getting bigger. If the pressure remains high, the muscle continues to thicken until the valve no longer is able to completely close. This causes blood pressure to rise in the veins leading to the heart, especially from the liver. The result is an increased pressure in the liver with leakage of blood fluids, without the red blood cells, into the body cavity forming ascites.

What causes it?

1. The genetics of meat birds has changed dramatically in the last ten years. Today's broilers grow much faster, eating less feed. The growth of the heart and lungs has not increased in size proportional to the increase in body weight and breast meat yield. The rapid growth of the bird means more oxygen demand, requiring more work out of the heart and lungs.
   
2. Anything that limits oxygen uptake from the lungs is going to cause the heart to work harder. Diseases of the lungs and poor ventilation may be involved.
   
3. Excess levels of sodium in the water or salt in feed leads to increased blood pressure in the lungs. Many well waters in Alberta have high levels of sodium. Levels of sodium over 400 ppm could cause problems in broilers.
   
4. High altitudes have long been known to cause heart failure and ascites.
   
5. Chilling is a common cause in small flocks. It causes an increased blood flow through the lungs.

Signs of the disease

Broilers with ascites look bluish because they are not getting enough oxygen in their blood. They have trouble breathing and often just sit and pant. They tire out easy and often die on their bellies. When it occurs within the first week of life, too much salt in feed or water usually is involved. Because the heart failure takes time to develop, most deaths begin at about 3 weeks of age.

Birds that die from ascites are quite easy to recognize. If their belly is opened as in proceeding to clean the bird, a cup or more of fluid or jellied material will pour out. Sometimes birds with the condition die from the effects of too much blood and fluid in their lungs before there is any significant amount of fluid in the body cavity.

Control

Ascites can be controlled by slowing the growth rate of the birds to reduce oxygen requirements. This can be done by restricting feed, feeding a mash diet, or using a less dense (lower energy and protein) diet. The other things causing ascites need to be controlled. If your water has high levels of sodium, consider using an alternate source of water that is better quality for the first 3 - 4 weeks. Take care to prevent chilling or overheating while at the same time maintaining proper ventilation.

Summary

As one can see, the cause of ascites is increased blood pressure in the lungs leading to a failing heart. The things that can lead to increased pressure and a failing heart are many. There is no one easy solution. Losses from the condition can be greatly reduced once problem areas are identified and eliminated.