Like other mammals, rabbits possess two kidneys. The kidneys are essential for filtering out toxins from the body and excreting them via the urinary system.
What are the kidneys for?
Rabbits produce alkaline urine and rely heavily on renal excretion as the major route of getting rid of any excess calcium within the diet. A rabbit's calcium metabolism is completely different when compared to that of other mammals because blood calcium levels reflect their dietary intake. This means that if the diet consists of too much calcium, this alone can cause problems. Furthermore, the rabbit depends greatly on kidney function to regulate the metabolism of calcium in the body. The calcium that is eliminated via the kidney can precipitate the urine forming crystals that give the rabbit's urine its typical creamy appearance.
There are numerous reasons why a rabbit's kidneys may fail or the efficiency of them may lessen. Unlike the liver, kidneys do not possess any regenerative powers, so once the kidneys have been damaged or disease has become apparent, the damage cannot be reversed.
What is acute kidney (renal) failure?
Renal failure is when the kidneys fail to filter the toxins and waste products from the blood properly. Acute renal failure happens over a short period of time, but clinical symptoms may involve reduced appetite and reduced urine production, which may go on to a cessation of appetite and urine production altogether. The rabbit may become depressed, dehydrated and grind its teeth in a painful manner (bruxism). Secondary gastrointestinal problems may also arise.
Clinical examination may reveal enlarged kidneys and uraemic odour from the rabbit's mouth.
Acute renal failure is often due to the ingestion of a harmful substance; these commonly include lead batteries, anti-freeze and nephrotoxic drugs.
Treatment involves aggressive fluid therapy to correct the dehydration and in the hope that the toxins can be flushed from the body in time before any long-term damage is done. However, the longer the problem has gone untreated, the poorer the prognosis. All potentially toxic drugs should be discontinued immediately.
What is chronic renal failure?
Unlike acute renal failure, chronic renal failure may develop over many days or weeks, and the clinical signs may go unnoticed for some time.
Clinical signs can include weight loss, gradual reduction in appetite, increased urine production and increased water consumption. The rabbit may lose body condition and generally look 'unwell and scruffy'.
A clinical examination will detect small 'shrivelled' kidneys which may feel irregular in shape. A blood sample is invaluable in these cases as it may show an increase in some parameters which may be indicative of a kidney problem. In particular, examination of the blood may show elevated creatinine, although urea is unlikely to be raised until over 50-70% of kidney function has been lost.
Potential causes of chronic renal failure include E. cuniculi infection, bacterial infections, sludge/stones within the kidneys and renal tumours.
Treatment is aimed at treating the underlying cause of the renal failure, whilst supporting the rabbit's kidneys and ensuring they remain hydrated and their gastrointestinal tract doesn't go into stasis.
Pain relief is also recommended, but all non-steroidal anti-inflammatory drugs (NSAIDs), such as Metacam® (meloxicam; Boehringer Ingelheim) or Rimadyl® (carprofen; Zoetis) must not be given due to their harsh nature on the kidneys.
A prognosis will depend on the severity of the kidney damage and the underlying cause of it. If this cannot be corrected/managed, then the prognosis is extremely grave.
What is polycystic kidney syndrome?
This has been reported in rabbits whereby small, multiple cysts have been located in the kidneys. Most rabbits with the condition show symptoms of chronic renal failure by the age of 2-3 years, which is often inherited. It has many similarities to polycystic kidney disease seen in humans and cats.
What about renal cysts?
These seem to be an incidental finding in rabbits and have often been diagnosed on ultrasound examination whilst looking for other problems.
Cysts don't seem to cause any impairment to the function of the kidneys, and treatment is not required.
Can rabbits only have one kidney?
Some rabbits may be born with only one kidney, which can affect both bucks and does. The rabbit may show no symptoms and lead a perfectly normal life, however, if their one kidney becomes disease in any way, and its function is compromised, then the rabbit's prognosis is grave.
What is nephrectomy?
This is the term given for the surgical removal of one kidney.
If one of a rabbit's kidneys is diseased to the point where it is causing the rabbit pain or problems, then it is possible to remove the diseased kidney. The surgery is a major undertaking and serious consideration should be given to the rabbit's welfare and long-term prognosis before proceeding.
If the rabbit's other kidney is diseased or not working properly, then the prognosis is extremely grave.