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Other Names: Kidney Stones, Urinary Calculi
Urolithiasis is an acquired degenerative kidney disease that occurs sporadically in chickens worldwide.It is characterized by focal mineralization of the kidneys and progressive obstruction of the ureters by uroliths (kidney stones). A normal, healthy hen's kidneys appear symmetrical in appearance, in shape, color, and weight. When hens develop kidney stones, if they get large enough or when large amounts accumulate, it can result in a blockage of the ureter that will cause the kidney tissue to atrophy; this can occur in one or both kidneys. As long as at least one third of the combined mass of a hen's kidneys are functional, she will still survive and continue to lay eggs. If kidney stones form and cause a blockage in both kidneys, it will lead to fatal renal damage which manifests as visceral gout (visceral urate deposition), followed by death.
The most common causes for previous documented outbreaks of urolithiasis in laying hens have been related to improperly mixed feed, feeding young chicks and pullets feed that is intended for egg laying hens, and water deprivation. There has also been suggested involvement of the nephropathogenic Infectious Bronchitis Virus (IBV).
Case 1: Urolithiasis in a Commercial laying hens An outbreak of urolithiasis characterized by high mortality and emaciation in a flock of leghorn pullets occurred. Clinical signs consisted of swollen feet associated with articulate gout. Visceral gout, atrophy, or irregular hypertrophy of the kidneys were also observed. Many birds had one or both ureters enlarged with white uroliths. Microscopic lesions were urate granulomas, necrosis and loss of kidney parenchyma associated with tubular dilation, and edematous and fibrotic interstitium. Ref
Case 2: Urolithiasis in a Commercial laying hens An outbreak of urolithiasis that doubled the annual mortality rate of chickens in a large flock of table-egg-layers occurred. Despite the presence of a large unilateral urolith and/or severe renal atrophy, the layers often maintained active egg production and apparent homeostasis until a small urolith blocked the ureteral flow from the contralateral kidney. This terminal episode appeared to produce acute obstructive renal failure, rapidly developing visceral gout (visceral urate deposition), uremia, and death. The atrophy observed appeared to be acquired and progressive. Histologic features in the kidneys were acute to chronic glomerulonephritis, interstitial nephritis, and pyelonephritis. Epizootiologic and microbiologic studies indicated that a combination of infectious and noninfectious mechanisms may have been involved. Causative roles for calcium-phosphate imbalance, infectious bronchitis (IB), Newcastle disease (ND), and adenovirus or reovirus infections could be neither excluded nor confirmed. Contributory factors may have been spray ND-IB and other vaccinations of 15-week-old ND-IB-susceptible pullets, water deprivation, shipping stress, Mycoplasma synoviae infection, immune complex disease, and mycotoxins. Ref
Case 3: Infectious bronchitis virus causing renal damage in a Commercial laying hens Avian urolithiasis syndrome was diagnosed in 14-to-25-week-old chickens from a multiple-age caged-layer complex housing more than 2.5 million chickens. Losses from this syndrome ranged from 0.5 to 1.0% per week. Seven-to-14-week-old pullets from this facility had multifocal renal tubular necrosis leading to interstitial fibrosis, tophus formation, and tubular dilation. A coronavirus was isolated in embryos inoculated with pooled samples of trachea, kidney, and cecal tonsil of 4-week-old pullets. This virus, identified as 85-209, was related to infectious bronchitis virus strain Florida 88 by hemagglutination-inhibition assay. Day-old specific-pathogen-free chicks were inoculated with fifth-embryo-passage amnioallantoic fluid containing this virus. These chicks developed histologic lesions of tracheitis at 5 to 7 days postinoculation. Half the chicks inoculated by eyedrop developed renal tubular necrosis after 7 days. Urolithiasis in the flock investigated was attributed to renal damage by this strain of infectious bronchitis virus occurring in 4-to-7-week-old pullets and progressing to segmental atrophy, hyperplasia, and ureteral stone formation in 14-to-25-week-old chickens. Ref