Gout is an inflammatory crystal-deposition disease caused by the super saturation and precipitation of sodium urate crystals or urates in tissue. Gout occurs as a result of impaired excretion by the kidneys (damaged kidneys) or overproduction of uric acid by the body (the kidneys can't get rid of the excess urates fast enough). When urate accumulates in a supersaturated medium, it can deposit in soft tissue or bones and form a tophus. Tophi can be present over extensor areas of the limbs, pressure areas such as the footpad, and along the shanks.
Gout occurs in chickens as two forms: articular and visceral. Each form differs by where the uric acid buildup occurs within the body and have distinct causes, morphologies, and pathogenesis.
- Articular gout:Articular gout is a chronic process resulting in deposition of urates and resultant granulomatous inflammation in the joint spaces, most often the feet. The cause of this form of gout is not clear, however it is suspected that diet and genetics are probable contributing factors.
- Visceral gout: Visceral gout is characterized by small gouty tophi within the renal parenchyma and on the surface of the liver, heart and air sacs. When birds are severely affected, gouty tophi may also occur inside of the liver and spleen. The tophi incite very minimal to zero inflammatory response and accumulate much more rapidly than in articular gout. Visceral gout usually occurs secondary as a result of severe renal dysfunction, leading to hyperuricemia. The primary cause should be identified.
In some chickens, visceral gout and articular gout may occur at the same time.
Articular Gout versus Visceral Gout Comparison
|VISCERAL GOUT||ARTICULAR GOUT|
|Percent of flock affected:||Can be up to 100% of the flock||Individual birds|
|Gross lesions observed in organs after death|
|Kidneys:||Almost always involved. Abnormally sized and covered w/ white chalky deposits||May become involved. Usually appears normal unless the bird was dehydrated.|
|Joints:||May or may not be involved||Always, especially the feet|
Vitamin A deficiency
Secondary to urolithiasis
Immune mediated glomerulonephritis
Exposure to toxic substances
|High protein diet|
Excess dietary calcium in diet
High energy diet
Gout can occur as a result of a number of different factors, with the most common being diet, dehydration, viral infections, and exposure to nephrotoxic drugs or toxins.
- Excess dietary calcium: Feeding non-laying chickens (such as chicks, pullets, roosters, and aged hens that don't lay eggs anymore) a high calcium diet for an extended period of time can cause kidney damage. This is most commonly related to feeding all flock members commercial laying hen feed. It can also be caused by a feed mill error, feeding an abundance of table scraps or treats that contain high amounts of calcium, and by providing low-quality poultry feed that contains large particles of calcium carbonate (CaCO3).
- Vitamin A deficiency: Vitamin A is an essential vitamin for chickens, and if they are receiving a vitamin A-deficient diet for any length of time, it can cause damage to the lining of the ureters (the ducts by which urine passes from the kidneys to the cloaca), leading to gout. Not all commercial chicken feeds contain vitamin A, and in those that do, the amount degrades over time, especially when it is exposed to sunlight. This is because vitamin A is very sensitive to sunlight. Chickens that do not have regular access to pasture grass are at a high risk of vitamin A deficiency, as grasses and various weeds (such as dandelion) are a good source.
- Low-Phosphorus diet: Chickens receiving a diet low in phosphorus are more at risk of developing gout, as phosphorus acts as a urine acidifier which helps in the prevention of kidney stones.
- High cholesterol diet: Chickens fed a diet high in cholesterol are more prone to developing renal disease.
Viral infectionsToxic substances to the kidneys
- Dehydration: If chickens become dehydrated, this puts them at risk of kidney damage. Dehydration is usually caused by lack of water, which most often is a risk during hot weather with increased water intake or during cold weather from lack of water access due to the formation of ice along the surface of the water source.
- Mycotoxins: Mycotoxins are toxins produced by molds that are commonly found in commercial poultry feeds worldwide, in addition to bedding materials, and other feedstuff. Ingestion of certain types of mycotoxins are known to cause kidney damage.
- Sulfa and Aminnoglycoside Antibiotics: These types of antibiotics are eliminated from the body through the kidneys, and are known for causing kidney damage to birds, particularly when chickens are not drinking enough water.
- Disinfectants and insecticides: Are safe and effective when used properly in accordance to manufacturer recommendations, however they can cause kidney damage when the dosage is miscalculated.
- Sodium bicarbonate (baking soda): Giving chickens sodium bicarbonate (which is sometimes administered during periods of hot weather and/or to improve egg shell quality) can contribute to the onset of gout by disrupting the pH of the urine, making it more alkaline, and putting chickens more at risk of kidney stones.