Characterization and composition of uroliths from domestic fowl

Urolithiasis (kidney stone formation) is an acquired degenerative kidney lesion affecting sexually mature and immature domestic fowl. For the present study, uroliths were collected from three commercial flocks during outbreaks of urolithiasis. Uroliths also were collected from a research flock in which urolithiasis was induced by feeding immature chickens a diet formulated to contain excess calcium (3.25% Ca) and .4% available phosphorus. All uroliths were tested by x-ray diffractometry, infrared spectrophotometry, and emission spectrography. With one exception, the stones were composed of compact masses of microcrystalline to fine pleomorphic crystals of calcium sodium urate, with random substitution of magnesium for calcium, and potassium for sodium. No initiating nidus was evident. One of four stones from one laying hen flock was positively identified as an ammonium acid (hydrogen) urate. The unique calcium-sodium-urate stone composition in all but one of the stones tested suggests that similar processes were involved in stone formation in the four different flocks.