By General Beven Mundida
What is Ascites?
In the last few years, ascites has become a major cause of wintertime mortality in broiler chickens. Whilst it is recognised that this condition is a frequent occurrence associated with fast-growing birds, much can be done to minimise the impact on the broiler flock. Ascites is not a disease caused by a virus or bacterial organism, although disease may also be one of the predisposing factors. Consequently, there is no treatment – only prevention through management. This article attempts to outline the principal causes, development, prevention and control of ascites in broiler chickens.
The causes of ascites.
Ascites is a syndrome that cause an accumulation of fluid in the abdominal cavity (“water belly”), as a consequence of heart failure. It is a production syndrome related to rapid growth rate and high oxygen demand or poor brooding conditions. This condition is more scientifically know as pulmonary hypertension syndrome and may or may not end up as ascites. In fact, some birds that might be recognised in the chicken house are flippers may actually be mortalities that are a result of pulmonary hypertension. It is this high pressure that will cause plasma leakage from blood vessels to accumulate in the abdominal cavity.
Broiler chickens, by nature of their ability to consume larger quantities of feed and grow rapidly, have an extremely high demand for oxygen. Generally, the bird’s cardiovascular system can accommodate this demand, with the heart pushing blood efficiently through the whole lungs where oxygen exchange occurs. When there is an increased demand for oxygen, as with poor ventilation, the heart essentially pushes the blood through the lungs harder to increase oxygen supply for the bird’s metabolism. Because the lung and cardiovascular capacity is fixed, there comes a point at which the lung can no longer accommodate any more blood supply from the weakening heart. This is the starting point of heart failure.
What cause Oxygen demand in broiler chickens?
Healthy, fast-growing chickens are efficiently utilizing all available oxygen to convert feed to bone and muscle while at the same time maintaining optimum body temperature and body function. Pulmonary hypertension happens when the heart is unable to push sufficient blood through the lungs (pulmonary), thereby significantly increasing the blood pressure (hypertension).
Multiple factors such as ammonia build up, poor ventilation, cold temperatures, rapid growth rate, high density diets, vaccine reactions, respiratory diseases and aspergillus, act to produce a tissue level oxygen deficiency.
This sets in motion the heart failure condition described above. While there is undoubtedly room for responding to some increased oxygen demand, some birds can be on the edge and will tip over into heart failure with any increase oxygen demand. The greater the demand imposed on the flock, however, the more cases of clinical ascites we are likely to see.
The thermo-neutral temperature for a fully feathered chicken in 24 degrees. At this temperature the bird does not need to use energy to create heat and cool down. As the air temperature varies from this point, the bird’s body must respond, using energy and therefore consuming oxygen. While both excessive and insufficient air temperatures increase oxygen demand, the greatest need is with low temperatures.
A study carried out in Alberta (Bill Cox, 2001), indicated that average temperature fluctuations of 3 degrees above and below industry guidelines recommended for that breed, was positively correlated to the occurrence of ascites.
How can Ascites be minimised
- Houses must be sealed to prevent drafts and optimised air flow.
- Houses should be well insulated to provide as little temperature fluctuation as possible. Ideally, temperature fluctuation (range) should be less than 2 degrees in any 24 – hour period.
- Adequate heating capacity is needed to maintain temperature, at the same time maintaining adequate oxygen for the birds.
- Pre-heat the brooding area for at least 48 hours before chick placement.
- Litter temperature should be a minimum of 32 degrees for forced air heaters 40.5 degrees for radiant type heaters underneath the heat source.
- Temperature should be based on the bird’s thermo-neutral zone, because its demand for oxygen is always at its lowest when the bird is at its thermo-neutral zone.
- Temperature should also be adjusted according to the relative humidity.
- The bird is the best judge of temperature. At all times, the birds should be:
- Softly chirping
If the birds are not doing all these things, then the environment must be adjusted. When the birds are sitting close to the floor with their heads kept low, they are cold and the environment must be adjusted.
- Keep air quality optimum, by moving air regularly and efficiently. In colder months it is better to add heat and keep the air moving than to shut down vents or reduce air flow in effort to conserve heat.
- Minimum air ventilation must never be sacrificed. Minimum ventilation but be increased if the carbon dioxide level exceed 3000ppm.
- Avoid build up of ammonia and avoid wet litter.
- When birds are in darkness, their heat production goes down and demand of oxygen decreases making them more metabolically efficient.
- The lighting programme must be in one block rather than multiple blocks.
- Some lighting programmes commences after 150-160 grams in weight depending on level of management.
- The lighting programme should reach peak darkness by 350 – 400 grams in weight.
- The lighting programme needs to be maintained until at least 1kg and then slowly reduced depending on growth and rate and market weight.
In general, we have seen older birds responding well to 4 to 6 hours darkness. Please note that lighting programme is not a feeding programme. It is a tool that is used along with good management to help reduce the incidence of ascites.
- Lower density feeds reduce growth rate and may reduce ascites.
- Mash/crumb feeds reduce growth rate and may reduce ascites.
- Reduce stress in the flock. While we may not know all the stressors that can affect broiler chickens, we can address those that are obvious.
- Keep stocking densities optimum.
- Walk the broiler houses often and carefully.
- Provide optimum feeding and drinking space.
- Disease may also predispose birds to ascites, from a stress point of view.
- If the birds are affected by disease consult your vet or technical advisor who should be able to recommend a treatment programme.
- Avoid prophylactic use of antibiotics.
It should be noted that there are other factors that can contribute to ascites, such as growing at high altitudes. The intent of the article, however is to address factors that can be controlled in the management of the broilers.