ACKNOWLEDGEMENTS

Urinary system pathology is relatively uncommon in equine compared with other domestic animals. However, urinary calculi have occasionally been encountered⁷. Most equine urinary calculi are found in the urinary bladder although ureteral, urethral and renal calculi also occur². But the pathogenesis of equine calculi is poorly understood⁵. A rare case of cystic calculi encountered in a horse is reported in this paper.

A 3 years old colt was brought to the Department of Veterinary Pathology, Madras Veterinary College, Chennai-7 for necropsy examination with a history of sudden fall in stable and collapse in spite of intensive treatment.

Necropsy examination revealed a blackish wound measuring about 5 cm around the anterior coronet region of the right hind hoof. About 50 ml of clear serous fluid in the pericardial sac, scattered petechiae in the ventricular endocardium and tracheal mucosa, pneumonia, congested spleen, enlarged, pale, pitted kidney with cortical capsule adhesion, Habronema sp. nodules in the stomach, greenish liquid contents in intestine were also recorded. Comminuted fracture of 14- 18^th right ribs at their middle was observed. A sabulous calculus (large, slightly hard, grayish-white gritty, sand like substance) weighing about 3 kg and measuring about 25×15 cm in size occupied the entire distended bladder (Fig.1).

Microscopical examination of calculus showed combination of calcium phosphate and struvite (magnesium ammonium phosphate) crystals (Fig. 2). Quantitative crystallograpghic analysis⁶ of calculus revealed composition of calcium phosphate (55%) and struvite (45%) crystals. Equine urinary calculi are generally composed of calcium carbonate⁵,⁷ but in this case it contained calcium phosphate and struvite crystals. Sabulous calculus of such a large size was not reported earlier. Renal excretion of calcium is important in equine calcium homeostasis and horses are able to excrete large calcium loads in concentrated urine⁹. It is possible that in horses with urolithiasis, excess renal excretion leads to hypercalcuria or there is deficiency of crystalline inhibitors⁵.

Occurrence of calcium phosphate might be attributed to deficiency of pyrophosphate. Pyrophosphate is mainly responsible for 50% of inhibitors activity against calcium phosphate crystals formation in human urine¹. Occurrence of struvite urolithiasis in humans and dogs appears to be almost exclusively a consequence of urinary tract infection whereas the majority of urolithiasis in cats and sheep are not associated with infection⁸.

Fig. 1:Horse: Distended urinary bladder with a sabulous calculus

Fig. 2:Urine sediment: Calcium phosphate and struvite crystals ×80

Fig. 3:Subacute cystitis with adherent granular crystal. HE×320

Histopathological examination of urinary bladder revealed denuded and desquamated transitional epithelial cells with some granular materials adherent to the surface of epithelium (Fig 3) and moderate amount of collagen deposition with fibroplasia and multifocal mononuclear cell infiltration in subepithelial stroma.

Cultural examination of urine, calculus and heart blood swab revealed the presence of Staphylococcus aureus, which was confirmed by biochemical characters³,⁵. S. aureus organisms could have entered into body through the wound on the right hind hoof⁴ and produced infection in the urinary bladder. Urinary tract infection with coagualse positive Staphylococci bacteria allows splitting of urea into two ammonia molecules, which are rapidly, hydrolyzed to ammonium ions, a component of struvite crystals. S. aureus infection, the cause for the subacute cystitis, might have precipitated development of calculi in the urinary bladder in the present case.

ACKNOWLEDGEMENTS

The authors are grateful to M/s. K.J.Hospital, Chennai for crystallography analysis.

A rare case of cystic calculi in a horse