Have you ever found a broiler dead on its back and wondered what happened? Chances are that bird had a heart attack. It isn’t terribly uncommon if you’re raising Cornish Cross broilers on pasture. They’re more prone to a disease called ascites (or water belly), which often leads to heart attacks and the loss of the bird.
Quick answer: Ascites, also called water belly, is a buildup of fluid in the body cavity caused by right-sided heart failure. It’s most common in fast-growing broilers like Cornish Cross raised on pasture, and most deaths occur after about five weeks of age.
What is ascites in chickens?
The scientific answer: it’s a disease caused by pulmonary hypertension that results in failure of one of the heart’s four chambers, specifically the right ventricle. Think right-sided congestive heart failure. Ascites syndrome develops when pressure rises in the pulmonary arteries as the heart works to pump more blood through the lungs to meet the body’s oxygen demand. The volume and pressure overload on the right ventricle leads to right heart failure, and ascites.
What causes ascites in chickens?
There are a few causes of ascites: high elevation, poor air quality, a cold and damp chill, and even the breed of bird. High elevation and poor air quality work the same way, by limiting oxygen. When the body’s oxygen requirement isn’t met, pressure builds on the right ventricular wall and fluid collects in the body cavity, which causes heart attacks.
We often see ascites in pasture-based operations because broilers are exposed to the elements. At some point on pasture it rains, and if you’re raising birds in early spring or late fall, temperatures drop overnight. Pair wet ground and wet chickens with cold weather and the result is ascites. Chickens can get wet as long as they stay warm, but a cold, wet chicken will die later in life. Ascites doesn’t appear overnight; it usually takes a few weeks to fully show, with most deaths around five weeks and after.
Breed is another factor. Cornish Cross are not a hardy breed, which is why they’re more prone to this disease. In commercial houses ascites is less common thanks to improved genetics and temperature-controlled environments. Pasture-raised birds don’t have that controlled habitat. Because Cornish Cross simply aren’t robust animals, management should be adjusted accordingly. The biggest consideration is giving them a place to get out of the weather and, ideally, off the wet ground.
Symptoms of ascites in chickens
Young broilers can develop ascites syndrome, but mortality is highest after five weeks. Signs to watch for include:
- Discoloration of the skin — darkening of the skin and comb to a dark red or purple, and blue discoloration around the comb
- Ruffled feathers
- Difficulty breathing
- Lethargy
- Reduced growth rate
- A water belly (the abdomen filled with fluid)
- On necropsy, fluid around the heart and congestion of the lungs and liver
How to prevent ascites in chickens
These are the top three management practices to prevent or reduce the incidence of ascites:
- Make sure your brooder has proper ventilation to maximize oxygen and minimize ammonia and dust.
- If you live at high altitude (above 4,000 ft), feed a lower-calorie diet.
- When heavy rain is forecast, make sure your chicken tractor has well-constructed sides to keep rain out, and provide straw or shavings so the birds aren’t sitting on wet ground.
Part of raising chickens on pasture is letting them live in the natural habitat of the outdoors, foraging on fresh grass and bugs. The downside is more exposure to the elements. Cornish Cross grow fast and convert feed efficiently, but they don’t flourish in difficult conditions. If Cornish Cross are your broiler of choice, the goal is to manage their environment to set them up for success, since we’re adapting them to conditions they weren’t bred for. Starting birds on a quality non-GMO chick starter and grower feed and following a sound brooding plan both help. For more on raising healthy broilers, see From Hatch to Harvest and Raising Broilers for Meat Production.
References
Ascites Syndrome in Chickens. PoultryDVM. (n.d.). poultrydvm.com/condition/ascites-syndrome
Hargis, B. M. (2023). Ascites Syndrome in Poultry. Merck Veterinary Manual.