From Dog

Blood urea nitrogen (BUN) is a metabolic byproduct of cellular protein through metabolism associated with the urea cycle.

The normal serum levels in dogs is 3.1 - 9.2 mmol/L.

Elevated levels are associated with azotemia and are commonly observed in canine patients with dehydration, following exercise and in association with various renal diseases such as acute renal injury and chronic renal disease.

Reduced levels are usually associated with medullary washout due to diabetes mellitus and other causes of polydipsia.