Ascites in Chickens: Causes and Prevention

Ascites syndrome in chickens is a condition that leads to excess accumulation of body fluids in a bird’s abdominal region. It is also commonly called “water belly” or “Pulmonary Hypertension Syndrome” by Scientists.¹ Sometimes containing yellow protein clots², the accumulated body fluids vary in colour and consistency and could lead to complications with an affected bird’s health. Ascites may occur in any animal including dogs, livestock, birds and humans. However in chickens, broilers (meat-type chickens) are most likely to be affected due to their rapid growth rate. Winter also exposes chickens to ascites. During this time of the year, the poultry birds experience “cold stress” which among other adverse effects slows down the supply of oxygen to the heart and other parts of the body. This puts pressure on the heart, lungs and vein, disrupts an animal’s circulatory system and consequently leads to an accumulation of body fluids in the bird’s stomach. . In severe cases, ascites may be lethargic.

Body Fluid Regulation in Chickens

Every animal including chickens have body fluids. These fluids – blood, saliva, urine and mucus – are mostly composed of water. They are relevant to maintaining a bird’s normal body functions by transporting nutrients between cells, tissues, and organs. Body fluids also aid the excretion of wastes containing toxins out of the body. Specifically, saliva protects the mouth, aids feeding, and contains enzymes that help with digestion while mucus protects the lungs. Blood is required for survival. By producing red blood cells, it supplies a chicken with oxygen and hormones, and helps it to fight against diseases¹. Although body fluids are essential, an accumulation may lead to harmful conditions like ascites. A healthy and functional system should be capable of maintaining a safe balance between fluids to be circulated and those to be excreted. Changes in body and environmental factors however may disrupt a chicken’s circulatory and excretory structure. This is harmful.

Causes of Ascites in chickens

The two kidneys located behind the lungs of chickens serve the purpose of absorption, filtration and excretion.  The kidneys contain erythropoietin which is a hormone that regulates the production of red blood cells (RBCs) by signaling the bone marrow to produce less or more RBCs depending on prevalent conditions. Red blood cells through respiration aid the transportation of oxygen round the bird’s cells and tissues. Afterwards, carbondioxide is produced and excreted from the body. When body metabolism increases either due to stress or rapid growth rate, the entire system changes. In response, the chicken’s body requires more oxygen to burn essential feed nutrients and meet up with increased energy demands. Consequently, the kidney through the erythropoietin signals the chicken’s bone marrows to produce more red blood cells for blood (oxygen) circulation. Unfortunately, while red blood cells are relevant to a system’s functionality, the production of excessive amounts of RBCs leads to blood clotting. Clots make blood denser, more viscous, and difficult to circulate. The inability to readily circulate blood and oxygen causes pulmonary arterial pressure which leads to the failure of the bird’s right ventricle or heart. The failure of the heart’s right ventricle due to increased pressure on the pulmonary artery causes that part of the heart to swell. The swelling increases pressure on the veins in that area leading to leakages and subsequent accumulation of fluids. The accumulation of these fluids in the bird’s abdomen is ascites. ³ Modern day broilers that grow rapidly are prone to this condition.⁴

The process through which ascites occur is caused by several factors including;

1. Environmental triggers: lower temperature reduces the supply of oxygen, causes stress to animals and increases the demand for oxygen. Cooler temperatures are associated with narrow blood vessels which restricts blood and oxygen flow. This is why ascites in chicken is more prevalent during winter. Also, chickens raised at higher altitudes⁵ also risk exposure to ascites due to a drop in oxygen at altitudes higher above sea levels.
2. Increased stress levels: overcrowding and unfavourable temperature are some causes of increased stress in birds. Heightened stress increase metabolism which increases the body’s demand for oxygen leading to a pressure on the lungs and possible heart failure.
3. Poor hygiene: overpopulation and poorly ventilated shelters restrict the availability of oxygen and induces stress among chickens. Failure to manage the situation may lead to lung and heart failure.
4. Salt intoxication: chicken feeds usually contain minute amounts of salt as a source of sodium for nerve impulses and to maintain water balance. However, when birds ingest excessive amounts of sodium, it leads to salt intoxication.  Salt intoxication among other adverse effects leads to severe respiratory disorder which puts a pressure on the bird’s lungs and heart.
5. Genetics: broiler chickens raised solely for meat production, cockerels and cocks have higher demands for oxygen⁵. The genetic make-up of these categories of chickens causes increased metabolism and consequent demand for more oxygen to fuel metabolism.

Signs of Ascites in Chickens

Ascites which can be detected between 4 to 5 weeks of a bird’s age is more likely to lead to the death of males.¹ The exposure of cocks to ascites arises from higher rates of metabolism and growth. Indicative signs of the condition in chickens include;

1. Swollen abdominal region;
2. Slower body development;
3. Panting;
4. Growling sounds;
5. Changes in skin color;

Prevention of Ascites in Chickens

Considering their high value as livestock animals producing eggs and environmentally safe and healthy meat (white meat), chickens should be protected from diseases that may lead to investment losses.

1. In severe conditions, feed reduction may be required to slow down growth rate and consequently oxygen requirement.
2. Good hygienic and management practices are required to destroy ascites-causing microorganisms like mold. By forming colonies in the lungs, molds infect a chicken’s air sac, leading to respiratory disorder and ascites. Chicken feeds can also be improved with supplements like acidifier to help them fight against molds and other microorganisms.
3. Temperature regulation: this is required to reduce stress levels and ensure adequate supply of oxygen. During winter, shelters should be kept warm and well-ventilated to prevent excessive loss of body heat which may lead to increased demand for oxygen.
4. Reduce sodium in chicken’s diet: the inclusion of salt in a chicken’s diet should be in line with recommended doses to avoid salt intoxication and respiratory disorders.

Reference

1. DSM: Ascites in Chickens – Water Belly. Retrieved on June 27, 2022 from https://www.dsm.com/anh/challenges/supporting-animal-health/ascites-in-chickens.html#:~:text=Ascites%20in%20chickens%2C%20commonly%20referred,dietary%2C%20environmental%20and%20genetic%20factors.
2. Hargis, B. M. (2014): Ascites Syndrome in Poultry. Published by MSD Manual in March 2014, modified in 2016 and retrieved in June 2022 from https://www.msdvetmanual.com/poultry/miscellaneous-conditions-of-poultry/ascites-syndrome-in-poultry.
3. Vascular Health Clinics: Heart Disease and Cold Weather. Retrieved on June 28, 2022 from https://www.vascularhealthclinics.org/heart-disease-and-cold-weather/#:~:text=Low%20temperatures%20cause%20your%20blood,and%20raises%20your%20blood%20pressure.
4. Gary Ritchison: Avian Biology. Retrieved on 27^th June 2022 from http://people.eku.edu/ritchisong/bird_excretion.htm.
5. Milsavljevic T. Ascites Poultry. Journal of Dairy, Veterinary and Animal Research. 2014;1(2):18-20. DOI: 10.15406/jdvar.2014.01.00006. https://medcraveonline.com/JDVAR/ascites-poultry.html.