Diagnosticians at the ISU-VDL have recently identified cases of fatal idiopathic nephrosis/renal failure in several feedlots geographically dispersed throughout Iowa. In those cases, very few of the calves on feed are clinically affected at any one time and the group as a whole may look remarkably normal; however, increased death loss accumulates over time.
Signalment: All known cases have originated from calves greater than 750 pounds (several near market weight). All confirmed cases have been from feedlot calves on feed for 4 weeks or more. No breed or sex predilection has been identified at this time.
Clinical description: Clinical signs described by submitting veterinarians in these cases include calves that abruptly go off feed, become markedly gaunt, and die within a few days despite therapeutic interventions. Other signs that have been occasionally reported include trembling, seizure activity, and bloody feces immediately prior to death. In cases encountered thus far morbidity is very low, often with just a single animal in a pen showing clinical signs at any one time. However, the clinical course in a group is cumulative with multiple animals sequentially affected over a period of weeks-to-months, and has approached 10% morbidity with up to 100% case mortality within a particular pen of cattle or within the same feedlot.
Clinical pathology: Serum chemistry testing of clinically affected animals has revealed elevated BUN, creatinine, and phosphorus.
Necropsy findings: Kidneys of affected animals have bilateral enlargement and are diffusely pale/yellow. On cut surface, the renal cortex is diffusely pale/yellow (see pictures below). In several cases normal amounts of rumen content is present with abomasal reddening, linear erosions, and scant intestinal and colonic content. Respiratory lesions have not been commonly found at necropsy. Lung lesions that have been present have been mild and limited to more chronic lesions such as fibrous pleural adhesions.
Histologic lesions: Microscopic lesions in the kidney range in severity but include dilated proximal and distal tubules lined by flattened epithelium, mild to moderate renal fibrosis, and scattered lymphoplasmacytic nephritis. Moderate to large numbers of crystals are present within collecting ducts near the cortico-medullary junction, with occasional crystals also noted in proximal and distal tubules. Crystals are birefringent with radiating spokes and are consistent with calcium oxalate.
Potential causes: To date, no definitive cause has been identified in these cases. Site investigations are underway to identify potential predisposing factors common to those feedlots with confirmed cases. Additional testing is also in progress in an attempt to rule out known nephrotoxic compounds.
Comments: The role of oxalate crystals is currently unknown. The presence of oxalate crystals may be due to exposure to soluble oxalates in the diet, but also may be incidental or secondary to previous renal damage. Either way, potential sources of soluble oxalates such as ethylene glycol and plants such as greasewood, sorrel, dock, halogeton, pigweed, lamb’s quarters, and rhubarb, among others, should be ruled out in suspect cases.
Our objective is to inform bovine veterinarians of the clinical description of these cases, to encourage client vigilance for unexplained deaths, and to assure that kidneys are evaluated during necropsy of all feedlot animals that fit this description.
If veterinarians at your clinic encounter any suspect cases, please contact Drs. Vickie Cooper, Kent Schwartz, Steve Ensley, Drew Magstadt, or Scott Radke at the ISU-VDL at 515-294-1950. Diagnosticians at the ISU-VDL are interested in investigating any confirmed or suspect cases that fit this clinical description.