By Claire Speight, Veterinary Nurse, C&G certificate in nursing exotic species, MBVNA

Urolithiasis (stones or sludge) within the urinary tract of rabbits, has been a ‘hot topic’ in the veterinary profession and amongst owners for several years. Many theories have been put forward and researched as to why rabbits seem to readily develop these deposits…but sadly there is still no hard facts as to exactly what causes these problems and how best to treat and prevent them from happening.

What is known, is that it is a complicated condition with many potential predisposing factors, treatment is life-long and often multi-tiered, and will frequently fail to prevent the condition reoccurring.

This article aims to discuss the latest thinking on the condition, what is thought to cause it and how to treat it.

How do rabbits metabolise calcium?

Rabbits are unique in the way that they metabolise calcium. The vast majority of mammals will only absorb the amount of calcium that they require from their diet and excrete less than 2% through their urinary tract. However, rabbits adopt a different approach, and absorb ALL the calcium from their diet, relying upon urinary excretion as the major route of getting rid of any excess (approx 44%).

The urinary tract in rabbits is identical to that of other mammals and exists of two kidneys, each with a ureter running from it to the urinary bladder. The urethra is the exit tract from the bladder, which enables the rabbit to pass urine out of their body.

As with all mammals, calcium is primarily required for muscle and nerve function, so the reason why rabbits have adopted this unique calcium metabolism is not fully understood, but may be linked to the constant growth of the rabbit’s teeth, which require a good source of calcium to ensure they grow correctly and the sparse diet that wild rabbits exist on.

What is urolithiasis?

Urolithiasis is the term used to describe calculi (stones) within the urinary tract. Calculi and sludge are slightly different things. They can develop in any area of the urinary tract but seem most common in the kidneys or urinary bladder.

What are the symptoms?

As with all conditions, symptoms will vary from rabbit to rabbit, with some exhibiting very subtle signs, and others showing severe discomfort and clinical signs.

Symptoms will include; anorexia or lessening of appetite, fewer or cessation of droppings, blood may appear in the urine (haematuria), loud painful grinding of the teeth (bruxism), lethargy, unwillingness to move, hunched posture, pressing their abdomen on the ground, perineal scalding, straining or inability to urinate and passing thick, white, toothpaste like urine. One or more symptoms may be present and may be very discrete. Symptoms can also be intermittent as the rabbits pain may come in waves as the stones/sludge move around.

Diagnosis

Radiographs and ultrasound are both diagnostic since both calculi and sludge are radio-opaque due to the calcium content.

Treatment options

The treatment will vary greatly due to the location of the calculi/sludge and the severity of the problems. Firstly, the rabbit must be stabilised and sufficient analgesia given, since the condition is so painful. Stabilisation may consist of aggressive fluid therapy: intravenous (directly into the vein) or if this is not possible then intraosseous (into the bone marrow) (as long as there is no obstruction of the urinary tract). Sub-cutaneous fluids are not going to be absorbed sufficiently rapidly if the rabbit is shocked, but are sufficient in the early stages and it is impossible to get enough volume of oral fluid into a rabbit in such cases. The rabbit’s gastro-intestinal (GI) tract must be kept moving, so prokinetic medication (Metoclopramide and Ranitidine) should be given and syringe feeding using a herbivore preparation (Oxbow Critical Care or Supreme Recovery) must be commenced at a rate of 50ml/kg/24hr if the rabbit is completely anorexic (less if the rabbit is still eating to some degree). If the rabbit will not tolerate syringe feeding then a naso-oesphageal tube should be placed for the purpose of providing nutrition.
Bloods should also be taken to assess the rabbits renal function (urea and creatinine) and the calcium level. This should be interpreted with caution as calcium levels will rise after meals, especially if the foods were high in calcium. A manual PCV (packed cell volume) is also useful to determine dehydration and any evidence of lipaemia (fat within the blood), which may be apparent if the rabbit is going into hepatic lipidosis.

Urinalysis is useful to determine if there are any crystals within the urine. Rabbits who are well hydrated, have a good level of pain relief and whose gastrointestinal tract is working, have a much better chance of surviving major surgery. So, only once the rabbit is stabilised (which may take several days) should surgery be attempted. The only exception to this may be with urethral calculi in buck rabbits who are not able to pass urine and when the calculi can not be pushed back into the bladder, or a urinary catheter inserted. These rabbits are surgical emergencies, and may require immediate life saving surgery.

Calculi within the urinary bladder are usually the easiest to remove. A procedure called a cystotomy is performed to remove the calculi. Urethral calculi are usually removed by flushing the stone back into the bladder and performing a cystotomy to remove it/them from the bladder. If calculi are detected within one or both ureters (ureterolithiasis), they can often cause hydronephrosis (an enlargement of the kidney due to the blockage of the ureter). Unlike the liver, kidneys do not possess any regenerative powers so it is impossible to improve the kidneys function once it has been damaged, but kidney parameters will only rise on blood work once over 70% has been lost, so it is possible for a rabbit to live a normal life with some degree of renal impairment. Ureteral calculi can be removed surgically, but it is a difficult procedure to perform on a rabbit due to the small size of a rabbit’s ureter, so referral is often required.
Those rabbits who present with calculi within their kidneys present a difficult dilemma. It is possible to perform a nephrectomy (removal of a kidney) in a rabbit, as long as the other kidney is free from disease. If both the rabbits kidneys are affected then it is often deemed unfair to put the rabbit through such a major procedure as a nephretctomy, since the other kidney is not likely to be capable of maintaining sufficient renal function. Attempts have been made to remove calculi from the kidney of a rabbit, but this surgery carries a very high risk of complications.

I am aware of rabbits who have had calculi removed from a kidney, but have sadly died shortly afterwards. And equally those who have gone on to live for several years on one kidney.The rabbits quality of life should always be the main consideration for the owner and the veterinary team.

Sludgy bladder

Thick, calcium sludge seems to be a common and often incidental finding in rabbits, but IT IS NOT NORMAL. The problem is indicative of a diet too high in calcium, and/or poor hydration, and it is often a pre-disposing factor of cystitis, which may be a cause of urolithiasis. If the problem is causing clinical signs (the same as those which may be shown with calculi), then it is possible to surgically flush the bladder. Although long term treatment should be aimed at reducing the calcium content of the diet and increasing the water intake.

Potential causes

Many factors have been sighted as causing urolithiasis in rabbits but no one single cause has been proved, and two rabbits fed identical diets, living identical lifestyles are both unlikely to develop problems, so the causes are liable to be numerous. No incidence of male/female, neutered/entire or breed incidence has been proven, but dwarf lop rabbits do seem to be affected more often. However, as they are one of the most popular breeds of rabbit kept within the UK, this may just be down to there being more cases as there are more of them.

Diets high in calcium

Rabbits fed a high calcium diet, which consists of alfalfa hay, calcium supplementation and vegetables high in calcium (kale, carrot tops, spinach, parsley and spring greens) are thought to be predisposed. Never feed adult rabbits alfalfa hay, unless they have a need for an increased calcium diet (pregnancy, lactation or growth of young rabbits). Limit the amount of high calcium vegetables offered and never use a calcium/mineral supplement/block. A rabbit fed a good quality diet has no need for calcium supplementation.

A low water intake

Less urine is produced when the rabbit has a low water intake, and calcium precipitates out when urine is saturated with calcium. In winter when water bottles or bowls may freeze over, the rabbit may have a period of time when it is without access to water, this may exacerbate over a period of time if the problem happens frequently. Rabbits with frequent bouts of gastrointestinal stasis will often not drink or slowly decrease their water intake. Rabbits drink more water when they are on a high hay or grass diet, and grass is additionally higher in water content as well.

Overweight rabbits

Those rabbits who are overweight are often unable to adopt the correct position for urination or may have weak muscle tone around the bladder. This gives any calcium in the bladder a chance to settle since the bladder is never fully emptied.

Lack of places to urinate

Rabbits who hold urine in the bladder give any calcium sediment a chance to settle, so always ensure that the rabbit has access to the area/litter tray it uses to pass urine.

Kidney disease

As aforementioned, kidney damage will only show up on blood work once over 70% has been lost, so those rabbits who appear healthy may have a degree of kidney disease. This can mean that the kidneys are not capable of processing the amount that is absorbed from the diet, enabling it to build up over a period of time.

Cystitis

Frequent bouts of cystitis often indicate a problem with the rabbits urination. They may not be able to completely empty their bladder due to back pain, being overweight, lack of places to urinate, painful scalding or sludge within the bladder. Any sludge within the bladder will irritate the bladder lining, causing cystitis, which may be a predisposing factor of urolithiasis.

Long-term management

Efforts must be made to remove all potential excess causes of calcium in
the diet and try to rectify any of the other pre-disposing factors:

  • Remove all commercial dried food from the diet and feed low/moderate calcium vegetables (celery, cauliflower, broccoli, carrots, brussels sprouts)
  • Feed low-calcium hays such as timothy or oat hay ad-lib. Never feed alfalfa hay
  • Sweeten water with apple/pineapple juice to try to get the rabbit to drink more
  • Add water to vegetables to increase water intake
  • Ensure that the rabbits water supply doesn’t freeze in winter
  • Encourage your rabbit to exercise to lose weight and encourage more frequent urination
  • Always ensure that your rabbit can get to it’s litter trays/toilet areas, so place several litter trays in their environment to encourage more frequent urination
  • Put your rabbit on a diet if they are overweight (consult your vet or veterinary nurse first)
  • Be vigilant for clinical signs of re-occurrence
  • Never breed from affected animals since hereditary problems have not been ruled out as a cause
  • If your rabbit has frequent bouts of cystitis, ensure they receive antibiotics but seek to find the route cause/s of the problem
  • If your rabbit has reoccurring episodes of gastrointestinal stasis then try to ascertain if there is a common cause.

Even after all efforts are made to stop further formation of calculi, it does have a high rate of recurrence.
More research is needed into the condition, and new information is being gleaned all the time, which will enable us to enhance our understanding of these problems.