Bilateral hydronephrosis during pregnancy in a Korean native cow

Hydronephrosis in cattle refers to the dilatation of the renal calices and is congenital or acquired by urinary obstruction. It has been a major cause of hydronephrosis due to obstruction of the upper urinary tract by urolithiasis or neoplasm, especially in adult cattle. A 43-month-old Hanwoo cow at 4 months gestation was admitted for anorexia, depression, and urine dribbling. Rectal ultrasonography revealed a large pregnant uterus, absent urinary bladder, and dilated calices observed in the caudal pole of the left kidney. Percutaneous ultrasonographic images showed dilated calices in the right kidney. The serum biochemical pro-file showed azotemia (blood urea nitrogen, 90.11 mg/dL; creatinine, 7.28 mg/dL). Blood gas analysis indicated electrolyte ab-normalities, including hyponatremia, hyperkalemia, hypochloremia, and hyperphosphatemia. Urinalysis showed a urine specific gravity of 1.020, pH of 7.5, leukocyte count of 70 cells/µL, nitrates negative, and protein negative. White blood cells or struvite crystals were not detected on the urine sediment microscopy. To detect Histophilus somni, Escherichia coli, and Corynebacterium renale, polymerase chain reaction was performed. The alpha-hemolysin gene of uropathogenic E. coli was detected in the left kidney and urinary bladder. The left kidney measured 20 x 10 cm and was filled with urine, whereas the urinary bladder was small, and the bladder wall was not thickened. No characteristic histopathological findings were noted in the bladder and kidney; how-ever, macrophages were present. Therefore, the cow was diagnosed with bilateral hydronephrosis due to urinary tract obstruction by the pregnant uterus. To the best of our knowledge, this is the first report of hydronephrosis caused by a pregnant uterus in cattle. It was also the first report that severe azotemia and electrolyte abnormalities could be caused by hydronephrosis induced by a pregnant uterus in cattle. This provides the veterinarian with a new differential diagnosis for hydronephrosis in pregnant cows.