Renal thrombotic microangiopathy with membranoproliferative glomerular remodelling in a Japanese Black steer.

Detailed clinicopathological and ultrastructural characterizations of bovine renal thrombotic microangiopathy (TMA) remain limited. A 20-month-old castrated Japanese Black (Bos primigenius taurus) steer was presented with depression and severe azotaemia. Histologically, glomeruli varied considerably in size, with many being reduced in size and collapsed or with global sclerosis, whereas enlarged glomeruli were less frequent. Intraglomerular thrombi consisted predominantly of periodic acid-Schiff-positive hyaline material, while fibrin-positive thrombi were infrequent. Small arteries and arterioles had concentric wall thickening with marked narrowing of the lumina, and similar vascular lesions were observed in the jejunal submucosa also. Ultrastructurally, glomerular capillaries showed severe narrowing of the lumina, accompanied by frequent mesangial interposition and multilayering of the glomerular basement membrane. No electron-dense immune deposits were identified. These findings were consistent with subacute-to-chronic endothelial injury-associated TMA with membranoproliferative remodelling. This case provides a comprehensive clinicopathological and ultrastructural characterization of bovine renal TMA.