Ascites or Water Belly in Broilers

A broiler farmer at Gomoa Buduburam sent us a video in the fifth week of his batch. A bird sat on the litter with its abdomen hanging low and round like a water balloon, feathers ruffled, breathing with its beak open, comb dark purple. When he lifted it, the belly sloshed. He had found four like it that morning and another six dead, all among the biggest birds in the house. He thought it was a disease and wanted to know which antibiotic to give. It was not a disease in the sense he meant. It was ascites, and no antibiotic on earth would have helped.

Ascites, which Ghanaian farmers call water belly, is one of the most common causes of death in broilers over three weeks of age, and it is almost entirely a consequence of how the modern broiler is built and how it is managed. Cobb 500 and Ross 308 birds have been selected for decades to grow muscle as fast as possible. Their heart and lungs have not grown at the same rate. Push that bird hard with dense feed, hot afternoons, cold nights, poor air and high altitude, and the lungs cannot supply enough oxygen; the heart works harder to force blood through them, the right side of the heart fails, and fluid leaks from the liver into the abdomen. The bird drowns from the inside.

This guide explains the mechanism in enough depth that the prevention makes sense, the signs to watch for on the farm and at post-mortem, the management levers that actually reduce it, and what to do when a batch is already losing birds. Ascites is not a treatable condition once a bird has it, so everything here is about the birds that have not yet gone down.

The mechanism: a bird that outgrows its own lungs

The technical name is pulmonary hypertension syndrome, and the name describes the problem. A chicken's lungs are small, rigid and fixed to the ribs; they do not expand like a mammal's. The bird moves air through them using air sacs, and the capillary bed in the lung has very little spare capacity. A fast-growing broiler at four weeks has roughly doubled its muscle mass in a week, and every gram of that muscle needs oxygen. Demand for oxygen rises faster than the lung's ability to deliver it.

When oxygen falls short, the body responds by constricting the small blood vessels in the lung and by raising the output of the heart. Pressure in the pulmonary artery rises. The right ventricle, which pumps blood into the lungs, is thin-walled and built for low pressure; under sustained high pressure it enlarges, then dilates, then fails. Blood backs up behind the failing right heart into the liver and the veins of the abdomen. Fluid, a clear or yellowish serum, seeps out of the swollen liver into the abdominal cavity. That fluid is the water in water belly.

Anything that increases oxygen demand or reduces oxygen supply pushes the bird along this path. High growth rate, dense high-energy feed and cold stress (which raises metabolism) increase demand. Poor ventilation, high ammonia, dust, respiratory disease, carbon monoxide from charcoal brooders and altitude reduce supply. Salt in the water and sodium in the feed increase blood volume and make everything worse. The bird's own genetics set the baseline; the farm decides whether it tips over.

Why Ghana sees a lot of it

Ascites is classically described as a cold-climate and high-altitude disease, which makes farmers here assume it should be rare. In practice we see plenty, and for reasons that are specific to how broilers are raised in Ghana.

• Charcoal brooding in closed houses. Charcoal pots produce carbon monoxide, which binds to haemoglobin and reduces oxygen carriage. Chicks brooded for two weeks in a house with tarpaulin sides pulled down at night and a charcoal pot burning are being set up for ascites weeks later, even if they look fine at the time.
• Cold harmattan nights. From December to February, night temperatures in Kasoa fall to 20–22 °C and in the north to 15 °C. A three-week-old broiler with the heat turned off shivers, raises its metabolic rate and its oxygen demand, and the losses appear a week or two later.
• Feeding for speed. Farmers under pressure to hit 2 kg by 35 days for a Christmas or Easter market push high-energy finisher feed from week three and keep the lights on 24 hours. Fast growth is the single biggest driver.
• Poor ventilation in the rainy season. Curtains down to keep the rain out, wet litter, ammonia at eye-watering levels and 90 percent humidity. Every one of these reduces the oxygen the bird can take in.
• Salty water. Boreholes near the coast, from Kasoa through Winneba to Cape Coast, can have high sodium.

Losses typically start in week three, peak in weeks five and six, and hit the biggest, fastest-growing males first. A farmer who loses 3–5 percent of a batch to ascites, all of them the heaviest birds in the house, has lost the most valuable part of the flock and often blames a "disease" that antibiotics did nothing for. Farmers who lose birds this way batch after batch despite good management, particularly in the north, should consider a slower-growing bird such as Sasso; see our Sasso guide.

Signs on the farm and at post-mortem

Ascites is easy to recognise once you know it, and the post-mortem is the most conclusive one in poultry: there is a bird full of water.

In the live bird:

• Distended abdomen, soft and fluid-filled, sometimes with the skin over it reddened or the feathers parted; the belly sways or sloshes when the bird is lifted.
• Bird sits with legs spread, reluctant to walk; when it moves it waddles like a duck.
• Laboured breathing, open beak, sometimes a gurgle; the comb and wattles dark red to purple (cyanosis) from low blood oxygen.

At post-mortem:

• Clear, yellow or straw-coloured fluid in the abdominal cavity, from a few millilitres to several hundred, sometimes with strands of fibrin clot floating in it.
• Right side of the heart enlarged, flabby and dilated; the whole heart may be rounded and the pericardial sac full of fluid (hydropericardium).
• Liver swollen and congested, or in advanced cases shrunken, hard and mottled with a fibrin coating.
• Lungs congested, dark and wet.

Lever one: slow the early growth slightly

Broilers that are held back slightly in weeks one to three, then allowed to grow fully afterwards, reach almost the same final weight with far less ascites, because the heart and lungs get a chance to develop before the muscle demand peaks. This is called early growth restriction or a "lighting and feed programme", and every large broiler company in the world uses some version of it.

• Lighting. Give 23 hours of light for the first 3–5 days so chicks find feed and water, then reduce to 18–20 hours of light with 4–6 hours of continuous darkness from day 5 until about day 21, then increase again. Dark periods lower feed intake and metabolic rate at night, and the birds sleep, which is when the heart and lungs catch up. Our lighting programme guide explains the schedule.
• Feed form and density. Feed starter mash or crumble rather than pellets in weeks one to three; pellets are eaten faster and push growth. Do not move to a high-energy finisher before day 24–28, and do not add fat or extra oil to the starter to "boost" it.
• Controlled feeding. In flocks with a history of ascites, some farmers restrict feed to about 90–95 percent of ad libitum intake from day 8 to day 21, by weighing out the daily ration. This must be done carefully to avoid uneven birds, and only with enough feeder space for all birds to eat at once. It is not for beginners.

Weights are orientation targets for mixed-sex flocks under good management; farms deliberately holding birds back for ascites control will be 5–8 percent lighter at day 21 and catch up by day 35–42. Confirm feed formulations with your supplier and any programme changes with your veterinarian.

Lever two: air, and specifically oxygen

A broiler house in Ghana in the rainy season can have all four of the things that reduce oxygen supply at once: high humidity, ammonia, dust and, in brooding, carbon monoxide. Each of them on its own would be tolerable; together they produce ascites.

• Charcoal is the first thing to fix. If you brood with charcoal, the pot must be in a chimney or the house must have permanent openings near the roof that are never closed, even at night. Better still, move to gas or electric brooders. We see a clear pattern: farms that switch from charcoal to gas brooders report fewer ascites deaths at four to six weeks, even though the brooding period itself looked fine both ways.
• Ammonia. If you can smell it at bird height, it is above 20 parts per million and damaging the lungs. Wet litter is the cause. Fix leaking drinkers, turn or top up litter, and ventilate. Our litter management guide has the routine.
• Minimum ventilation at night. Curtains fully down all night in a full house is a common cause. Leave a permanent gap at the top of the side walls, protected from direct rain, so that stale air leaves and fresh air enters even in a storm. Ventilation is for air exchange, not just cooling.

See our house ventilation guide for how to achieve air exchange without draughts on a budget.

Lever three: temperature, both ends

Cold increases oxygen demand because the bird burns energy to stay warm. Heat increases it because panting is work and because the bird's heart races to lose heat. Both push a bird with marginal lung capacity over the edge, and in Ghana a single batch can experience both within a day: a harmattan night at 20 °C and an afternoon at 36 °C.

Follow the brooding curve (32–33 °C in week one, dropping about 3 °C a week to ambient by week four) and do not switch heat off abruptly at 14 days because the chicks "look big". In harmattan, keep some heat available at night until week four. In hot weather, reduce stocking density, provide cool water, wet the roof, use fans, and consider feeding in the cooler hours so that the heat of digestion does not coincide with the afternoon peak. Our heat stress guide and harmattan brooding guide cover each end.

Other contributors: water, feed and sodium

Sodium raises blood volume and blood pressure. Broiler feed is formulated with about 0.16–0.20 percent sodium, which the bird needs, but salt is cheap and easy to over-add in home-mixed feed, and coastal borehole water can contribute more. If you mix your own feed, weigh the salt to the gram; a heaped cup instead of a level one across a tonne of feed can double the sodium. If your water tastes even slightly salty, test it; a total dissolved solids reading over about 1,000 mg per litre or sodium over 50 mg per litre is a concern for broilers. Our feed mixing guide has the inclusion rates.

What to do when a batch is already losing birds

If you are in week four and finding purple-combed, big-bellied birds every morning, you cannot save the ones already affected, but you can reduce further losses in the two weeks that remain.

1. Cull affected birds today. They will not recover and they are suffering.
2. Open the house. Raise curtains, clear anything blocking vents, run fans if you have them, and fix ammonia by replacing the wettest litter.
3. Introduce a dark period. Four to six hours of darkness at night reduces feed intake and metabolic load immediately.
4. Step down feed energy. If you have moved to finisher early, go back to grower for a week. Do not starve the birds; just remove the push.
5. Check water salinity and feed salt. Switch to a different water source for a week if the borehole is suspect.
6. Add vitamin C and electrolytes to the water for the remaining period, especially in hot weather.

A mini-case: 1,000 Cobb 500, harmattan, charcoal

A farmer at Kasoa Ofaakor placed 1,000 Cobb 500 chicks from us in the first week of December. He brooded with two charcoal pots in a house with tarpaulin curtains pulled tight every night against the harmattan, fed 24-hour light, and moved to a finisher feed at day 21 to make weight for Christmas. First-week mortality was 1.6 percent, which is good, and the birds looked excellent at two weeks. From day 24 he began finding one to three dead birds a day, always large males, some with swollen abdomens. By day 38 he had lost 71 birds, over 7 percent, and had begun a course of antibiotics on the advice of a shop attendant, which changed nothing except his margin. His vet opened three birds and found clear fluid, enlarged right hearts and congested livers in all of them.

For his next batch, in February, he switched to a gas brooder, cut a permanent 20 cm gap under the roof line along both sides of the house, put a timer on the lights to give five hours of darkness from day 6, held starter until day 26 and finished on a slightly lower-energy feed. Day 21 weights were about 60 g lighter than the December batch. Total mortality was 3.1 percent, of which the vet attributed only a handful to ascites, and the birds averaged 2.2 kg at day 40, heavier than the December batch had been at day 42 because there was no antibiotic and no lost appetite. The gas brooder paid for itself in that one batch.

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