Blood Urea Nitrogen (BUN) in rabbits

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Urea is a nitrogenous waste product formed during the protein degradation in the liver. It circulates in the blood in the form of urea nitrogen, and is transported to the kidneys in order to be filtered and excreted by the kidneys. In healthy well-hydrated rabbits, most urea nitrogen will be filtered and excreted with the urine. The presence of urea nitrogen in the blood can be measured by the BUN test (blood urea nitrogen).

Reference level in a healthy rabbit: 13-30 mg/dl.

Unlike other animals, the level of BUN can be easily influenced by physiological or environmental factors in rabbits. It may reflect the state of stress of a rabbit at that specific moment (hydration status, transport, foreign persons and/or environment, unusual smells, barking dogs). It can be affected by the diet, the period of time that the sample is taken during the day (higher levels of BUN are observed in the late evening) or by medication (e.g. chloramphenicol, streptomycin, gentamycin, tobramycin, diuretics and corticosteroids). Further factors affecting the level of BUN relates to the presence of parasites like coccidiosis or to bacterial catabolism, by the bacteria of the cecum that use nitrogen during metabolic breakdown-reactions or during food abundance.

If the BUN level is found to be elevated, it is advisable not to rapidly conclude that the rabbit is suffering from kidney failure, unlike for cats and dogs. A second sample should be taken once the rabbit is well hydrated (but not over-hydrated) and be compared with the previously obtained result.

An elevated BUN level can be caused by:

· kidney failure;

· low volume of blood/plasma due to diarrhea (hypovolemia);

· blockage of the urinary tract by a kidney or a bladder stone, a tumor or a polyp;

· a heart disease;

· bleeding in the digestive tract;

· toxic insults.

A low BUN level can be caused by:

· over-hydration;

· malnutrition;

· liver disease or damage;

· medication;

· gestation.

X-rays or ultrasound can be made to detect enlargement of the kidneys, presence of stones, malignant tumor, cysts, fibrosis.

Exterior signs of kidney disease are a decrease in appetite, a loss of weight, lethargy, anemia, a need to urinate often, a need to drink much more than usual.

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