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Gout is caused by the buildup of too much uric acid in the bird's body. Uric acid is regularly produced in the liver and excreted through the kidneys into the urine. However, birds with impaired renal function may not be able to get rid of uric acid as efficiently, leading to a build up within the blood which is called hyperuricemia. Hyperuricemia can result in uric acid deposits within the joints (articular gout) and in visceral organs or other extra-visceral sites (visceral gout). Over time, these deposits will grow to form tophi (nodular masses of uric acid crystals).
What are the Different Forms of Gout?
Articular Gout: The accumulation of urates within the synovial capsules and tendon sheaths of the joints, including the toes of the feet.
Visceral Gout: The precipitation of uric acid crystals along the surface of internal visceral organs and other sites within the body.
Articular Gout Versus Visceral Gout
Percent of flock affected:
Can be up to 100% of the flock
Gross lesions observed in organs after death
Almost always involved. Abnormally sized and covered w/ white chalky deposits
May become involved. Usually appears normal unless the bird was dehydrated.
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
What Causes Gout?
A number of risk factors are associated with development of gout in poultry.
Diet-Related Risk Factors:
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).
High protein diet: When chickens are fed protein in excess of their nutritional requirements, the additional protein is converted into uric acid. This puts them at a higher risk of developing gout.
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.
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.
Avian nephritis virus (ANV): A type of astrovirus known for causing kidney damage. It is prevalent in commercial poultry flocks worldwide.
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.