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Avian species excrete nitrogenous wastes as urate bound in colloidal form with mucus in their urine. Renal disease decreases the clearance of uric acid from the blood, which results in acute or chronic hyperuricemia, and the excess uric acid precipitates on either visceral or articular surfaces (gout). Urate deposits are white and semisolid and must be differentiated from yellow fibrinous or purulent inflammatory exudates that are secondary to infectious causes of synovitis, peritonitis, perihepatitis, and pericarditis.
Acute urate deposition occurs after rapidly progressing renal failure, or as a terminal event with acute decompensation of chronic renal disease. Deposits develop most commonly on the pericardium, peritoneum, and liver capsule, and rarely on synovial surfaces of joints and tendons. They are usually present for too short a time to induce significant inflammation. Most clinical cases of acute renal failure and urate deposition in commercial poultry are due to dehydration, ingestion of feed containing >3% calcium by nonlaying chickens, renal infection by nephrogenic strains of infectious bronchitis virus, or infection with avian nephritis virus. Other avian species commonly develop visceral deposits secondary to nephrotoxin exposure, most commonly aminoglycoside antibiotics or heavy metals.
Chronic urate deposition is less common and occurs after long-term increases in serum levels of uric acid. Deposits develop on synovial membranes in the toes and wing joints and incite a chronic granulomatous reaction to urate crystals (tophus). Chronic urate deposition is most frequently seen in chickens that have hereditary defects in uric acid metabolism or that are fed excessive protein.
Urolithiasis is common in older laying chickens. Brittle, white, staghorn calcium urate calculi form in one or both ureters. Most cases are due to feeding high-calcium laying feed to hens not in egg production, infection with infectious bronchitis virus, or severe vitamin A deficiency. If blockage is complete, acute postrenal failure develops, and birds die with acute urate deposition on visceral surfaces and less commonly in joint spaces. If blockage is incomplete or unilateral, chickens survive in compensated renal failure, and chronic urate deposits form in joint spaces.
See Also:
Ascites Syndrome
Breast Blisters
Cannibalism
Fluke Infections
Pendulous Crop
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