By Claire King

Since my rabbit Saxon, developed calcium stones (also referred to as calculi, or urolithiasis) in April 1999, I have done extensive research into his condition and other calcium related problems in rabbits. This article is written using those findings and my personal experiences. I hope everyone whose rabbit is affected by a calcium related condition and even those whose rabbits aren’t will find it interesting and useful.

Some of the symptoms mentioned for these conditions, can, at times be attributed to conditions other than calcium problems, so always consult an experienced rabbit vet if you suspect your rabbit may have a problem and be guided by them. Never try to correct a problem unless you have a definite diagnosis as you could make things much worse.


Calcium is a very important mineral for rabbits: they need it to form strong and healthy bones and teeth (and so to prevent dental problems and osteoporosis) but just as too little calcium can cause problems, so can excess quantities.

It is suspected, that to some degree a large percentage of the UK’s pet rabbit population is deficient in calcium. Although calcium consumption isn’t the sole factor responsible for the development of calculi, it does play a major part; so getting your rabbit’s calcium intake correct can go a long way to preventing future problems.

Calcium Deficiency

Calcium deficient rabbits tend to be those, which are selective feeders and are allowed to leave the pelleted part of their dried mix, which usually contains the calcium and vitamin D supplementation.

Dental problems are the best-known manifestation of calcium deficiency in rabbits, although whether calcium deficiency is the only or main cause of dental disease remains controversial. Signs of dental disease are varied. Typical signs seen at a relatively early stage may include a discharge from one or both eyes; grooves on their incisor teeth; problems with the molar teeth; and perhaps changes in food preferences and a reluctance to eat hay.

If the calcium deficiency becomes moderate to severe, the symptoms will be much more readily noticeable. Teeth may become so weak that they crumble and come loose from their sockets; the rabbit will be at an increased risk of bone fractures (especially the lumbar spine) and bones deformities may occur. These are all serious conditions that require not only medical treatment, but also careful dietary adjustment to try to correct the underlying calcium deficiency.

Your vet may recommend a calcium supplement, which if given correctly will cause no problems, but the best long term solution is to get them to eat all of their pellets or rabbit mix, together with a selection of vegetables and good quality hay.

Extruded, nugget-type feeds (eg Burgess Excel and Supreme Selective) are now available, which prevent selective feeding and are more palatable than traditional compressed rabbit pellets. Most bunnies seem to like them, despite their unappetising appearance to the human eye! If you do feed a “muesli type” rabbit mix with different components, you have to be cruel to be kind – bowls should not be re-filled until all the food, especially the pellets, have been eaten.

Rabbits deficient in calcium may also benefit from sunbathing. Sunlight enables rabbits to produce vitamin D, which in turn enables the absorption of the calcium in their diet.

Excess Calcium

An excess amount of calcium can lead to a multitude of problems.

A rabbit fed on a good, balanced diet should not be calcium deficient and does not need a calcium or mineral supplement. The average sized pet rabbit (approx. 2.5kg) needs typically around 510mg of calcium per day. Any more and they may be predisposed to developing calculi (stones) or sludge‚ in their urinary tract system.

Rabbits have an unusual calcium metabolism. In most mammals, the amount of calcium absorbed from the diet is regulated at gut level by Parathyroid hormone (PTH), but in rabbits calcium absorption is less well regulated and they absorb calcium in proportion to what is present in their diet, whether or not they require it. Any excess calcium that is absorbed into the blood stream from the gut is excreted through the urinary tract, where it may be deposited and form calculi. Rabbits can form solid calcifications in their kidneys, ureters, bladder or urethra, as well as depositing thick calcium “sludge” in their kidneys or bladder.

Calculi (urinary tract stones, or urolithiasis)

One or more stones may develop, with or without sludge being present. In rabbits, calculi in the urinary tract are almost always made up of calcium components, with the vast majority of calcifications being made of calcium carbonate.

Symptoms of calculi being present may include:

  • loss of appetite
  • loud painful grinding of the teeth
  • hunched posture
  • lethargy
  • unwillingness to move
  • pressing tummy on the ground
  • loss of litter training
  • blood in the urine
  • perineal scalding
  • straining to urinate

One or more of these symptoms may appear over a period of time, or have a sudden onset.

Treatment depends upon the severity of the condition and the location of the calcification/s. Calcifications will show up on x-ray or ultrasound scans, as the calcium content makes them radio-opaque.

A blood test is useful to determine the kidney function readings (creatinine and urea) and the blood calcium level. Calcium levels must be interpreted carefully. For example, an ionised calcium level is a better indicator than a total calcium level; calcium levels will rise after a meal, especially if the food given was high in calcium; and the normal range of results in pet rabbits may differ from those obtained in laboratory rabbits, most of which are New Zealand Whites. A urine test should also be taken to see if calcium crystals and/or a urinary infection (cystitis) are present.

Calcifications detected in the bladder, ureters or urethra usually need to be surgically removed once the rabbit’s condition has been stabilised. Rabbits suffering from urinary tract calculi are often in a lot of pain and as a result will not eat or drink, subsequently being dehydrated and necessitating fluid therapy prior to surgery. There is no known method of breaking up rabbit calculi and it is extremely rare for them to be passed naturally by the rabbit, due to their often jagged texture and the size to which they can grow, so surgery is the only treatment option.

Rabbits presenting with calculi in both kidneys and showing obvious clinical symptoms have a guarded to poor prognosis. Surgically removing calculi from the kidney itself is a very hazardous undertaking, although such surgery is performed in other animals. For these cases medical management may be the only viable option, with their quality of life being paramount at all times. If the calculi are only located in one kidney, it may be possible to remove the affected kidney, as the remaining kidney will have enough function left to keep the rabbit alive. However, if the remaining kidney should become diseased and unable to work to near full capacity, the rabbit’s prognosis is extremely grave.

Calcium Sludge

A rabbit suffering from calcium sludge may display any of the symptoms described above with calculi, as well as passing thick, white, cloudy urine that in severe cases will resemble the texture of toothpaste and form into a mound when passed.

Diagnosis is much the same as that of calculi: as the sludge is made of calcium, it too will show up on an x-ray or ultrasound scan as a mass. Treatment depends upon whether the sludge is causing the rabbit a problem, as some healthy rabbits exhibiting no clinical symptoms, can upon x-ray, be found to have some degree of sludge in their bladder or kidneys.

If the rabbit is unwell‚ the sludge needs to be flushed from the bladder, which will usually require a general anaesthetic or at least heavy sedation. Sludge in the kidney is more difficult to eradicate. Although kidneys can be flushed, and such flushing may be adequate to return the kidneys to normal or near-normal working capacity (and hopefully the rabbit to live a normal life) it is unlikely to clear all the sludge.

Long Term Goals

Whether having had calculi or sludge, once the initial condition has been treated, the diet must be altered to prevent recurrence of the problem, but even then there is approximately a 10 -15% chance of further calculi or sludge forming, particularly if the rabbit still has sludge in their kidneys or bladder. These rabbits will need careful monitoring, usually consisting of blood and urine tests, as well as periodic x-rays to keep a close eye on the condition.

A rabbit with a past history of calculi or sludge problems should be fed a diet of low calcium fruits/vegetables and grass hay ad lib. Dried rabbit mixes should be excluded from the diet or fed in a tiny proportion as a very occasional treat. Any alfalfa based foods (such as alfalfa hay), should be removed from the diet.

Fruits and vegetables can be grouped into good, moderate and poor calcium providers. The calcium mg content per 100g of food is shown alongside in brackets:

Good Calcium Providers:

  • Kale (130)
  • Spinach (170)
  • Parsley (200)
  • Watercress (170)
  • Mint (210)
  • Spring Greens (210)

Moderate Calcium Providers:

  • Cabbage (49)
  • Broccoli (56)
  • Celery (41)
  • Lettuce: round/flat (53)
  • Parsnip (41)
  • Swede (53)
  • Turnip (48)
  • Oranges (47)

Poor Calcium Providers:

  • Brussel Sprouts (26)
  • Carrots (25)
  • Cauliflower (21)
  • Cucumber (18)
  • Lettuce: Iceberg (19)
  • Peppers: Red/Green (8)
  • Tomatoes (7)
  • Apple (4)
  • Apricot (15)
  • Banana (6)
  • Grapes (13)
  • Kiwi Fruit (25)
  • Nectarines (7)
  • Peaches (7)
  • Pears (11)
  • Pineapple (18)
  • Strawberries (16)

Alfalfa hay contains approx. 1.5% calcium, compared with 0.4% calcium in grass hay. These values will vary depending upon the soil that the hay was grown in and the time of year it was harvested.

Rabbits with excess calcium conditions should probably avoid all the foods grouped in the good calcium provider category, and have a limited amount of those in the moderate group. Their main fruit and vegetable intake should come from the poor calcium provider group.

Calcium deficient rabbits will benefit from being fed foods from the good‚ and moderate calcium provider groups, together with a good rabbit mix/extruded nugget and hay, though care must be taken not to feed a diet too high in calcium, otherwise urinary tract calcification or sludge may occur.

However, before you start keeping a calculator by the fridge to try and keep tabs of the exact composition of your rabbits diet, there are a few other factors to consider. All green leafy vegetables contain about 95% water, helping to provide the high fluid intake which is essential for rabbits suffering from urolithiasis. Plus, even those vegetables which provide the most calcium, are not really all that rich in calcium. For example, spring greens top the list, with 210mg calcium per 100g. This is still lower in calcium than a typical batch of timothy (grass) hay. Finally, it is important to make sure that phosphorus intake doesn’t exceed that of calcium. Do discuss your rabbit’s diet with your rabbit-experienced vet, and don’t forget that expertise is also available from nutritionists employed by feed companies both in the UK and US, who are usually happy to help individual rabbit owners.

Any change in diet should be done gradually (over at least a couple of weeks) to prevent digestive upsets. Try introducing one new food at a time and if it seems to upset the rabbit in the next 24 – 48 hours it should be excluded from the diet. It is wise to feed small amounts of lots of different foods, rather than larger quantities of a few foods. This not only gives the rabbit a variety, but it also ensures a complete nutritional balance of other minerals, as well as calcium.

The vast majority of rabbits on this “hay and veggie” diet cope perfectly fine and get through, on average, a mound of fruits/vegetables their own body size each day. Hay and fresh water should be available at all times.

Continuation of Calculi/Sludge Development

Sadly, even after strict dietary alterations, some rabbits still develop calcium calculi or sludge. This has been linked to a variety of possible reasons, but further research is needed to figure out which factors are the most important:

Low Water Intake

This is suspected to be one of the most important factors leading to the formation of urinary calculi. Less urine will be produced if the rabbit has a low water intake. Calcium precipitates out when urine is saturated with calcium. To try to rectify this problem you must get the rabbit to drink more and this can be achieved by:

  1. Adding apple juice or some other palatable sweet flavouring to the water.
  2. Give the rabbit a plain salt lick or sprinkle a small amount of table salt onto the rabbits veggies.
  3. If neither of the above work, then syringe feeding of fluids (or even regular subcutaneous fluids, injected beneath the skin) may be the only way of getting increased fluids into the rabbit.

Overweight Rabbits

Rabbits carrying extra weight, may be unable to completely empty their bladder, due to weak muscle tone, which will give any calcium in the urine a chance to settle in the bladder. Make sure they are the correct weight for their breed or if they are a cross bred make sure you can just about feel their ribs and they are able to reach their bottoms. These are good indications that the rabbit is a good weight.

Kidney Damage

The rabbit’s kidneys may be damaged and simply not able to cope with the calcium, which they are required to process. Kidney damage will only show up on blood tests when at least 50-70% of kidney function is lost.

Litter Training

Most rabbits are very clean in their homes and will only urinate in one or a select amount of places. If the rabbit is unable to get to these places (i.e. no litter tray in pen etc), then it may wait until it can urinate in its desired area. Holding onto urine in the bladder will cause the precipitation of calcium in the urine to rise, so always ensure your rabbit is able to reach its toilet area.


Even after a low calcium diet has been implemented and all the factors mentioned above looked into, if the rabbit still continues to produce calcium deposits, then a genetic reason must be considered. Some rabbits may simply be “stone/sludge producers” and whilst this can never be ruled out with any calcium problem, whether an excess or deficiency problem, rabbits affected with any type of calcium problem should never be bred from.


Some green foods (eg dandelions) are high in oxalate. Oxalates should be metabolised by bacteria in the gut, but if there aren’t enough oxalate-eating bacteria around, then the oxalate will be absorbed into the blood stream rather than broken down. It then has to be excreted via the kidneys, with calcium hitching a ride at the same time.

In other species, deficiency of the bacteria Oxalobacter formigenes has been linked to the formation of urinary stones. The population of this bacteria can be reduced by long-term antibiotic therapy, or simply if the animal isn’t eating oxalate-containing foods on a regular basis. It is not yet known whether this mechanism is important in rabbits, but this is certainly an area that deserves further investigation.


The conclusion that we can draw upon from calcium problems, both lack of and in excess quantities, is that we have been feeding our rabbits incorrectly for many years.

Rabbits are designed to live off grass and more grass. This keeps their teeth worn down, their digestive systems working properly and provides them with the correct nutritional values. Dried mixes are very convenient for us and although you may think your rabbit needs a bowl full of dried mix each day – they don’t!

Unless all the food is eaten and backed up with good quality hay and a variety of fresh fruits and vegetables, problems are liable to occur. Commercial rabbit food should only be a small percentage of the rabbits daily food ration and should be eaten within half an hour of being given. The rest of the rabbit’s time should be spent eating hay, grass (fresh or kiln-dried) and their fruit and vegetables.

Case Study : Saxon: Claire King

Saxon is my French Lop buck, who was diagnosed with calcium sludge in both his kidneys as well as a calculus in his right ureter in April 1999. This calcification was removed and his diet altered, but a further calculus formed, this time in his left ureter in June 1999. Again the calcification was removed and his diet restricted further.

At the present time he is on a diet of no rabbit mix (and has been since April 99), together with some of the moderate calcium fruits and vegetables and all of the poor calcium fruits and vegetables listed above. He lives perfectly well on this diet, with unlimited hay and fresh water and weighs a healthy 5.5 kg (12 lb).

Despite having his kidneys flushed when each calculus was removed, after 2 years they still have sludge in them, but regular blood tests demonstrate that his kidneys are unaffected by it. He has regular x-rays to determine if the sludge is beginning to disappear and to make sure no more calcifications are forming.

Saxon is living proof that although serious, calculi and associated conditions don’t have to be a death sentence and once the initial problem has been addressed and the diet altered there is a very good chance that they will continue to live a happy and fulfilling life.

Treatment for calculi and associated problems can be lengthy and indeed span the rest of the rabbit’s lifetime. It is this that makes me recommend insuring your bunnies from the outset. Petplan have a very good policy for rabbits. Without insurance you could be looking at a very serious financial commitment by the owner, running into hundreds if not thousands of pounds. To date Saxon’s treatment for his calcium condition has cost around £2500.


With thanks to Sally Machell and Dr Linda Dykes for reading through the original version of this article and all the vets and other professionals – particularly Dawn Hromanik – who have shared their knowledge on this subject with me, to enable me to write this article.

Recommended Reading

If you want to know more about rabbit nutrition or the veterinary area of rabbits, then the following books come highly recommended.

  • Rabbit Nutrition: Virginia Richardson MA VetMB MRCVS. ISBN: 1-898015-03-1 (Coney Publications).
  • Rabbits; Health, Husbandry and Disease: Virginia Richardson MA VetMB MRCVS. ISBN: 0-632-05221-X (Blackwell Science).
  • The BSAVA Manual of Rabbit Medicine and Surgery: Edited by Paul Flecknell MA VetMB PhD DLAS DiplomateECVS MRCVS. ISBN: 0-905214-46-3 (British Small Animal Veterinary Association).
  • Rabbit Lopaedia: Meg Brown and Virginia Richardson MA VetMB MRCVS. ISBN: 1-86054-182-8 (Ringpress Books).
  • Textbook of Rabbit Medicine: Frances Harcourt-Brown. ISBN: 0-7506-4002-2 (Butterworth-Heinemann)

This article appears on the RWF website by kind permission of the author, Claire King.

It first appeared in the Sept/Oct 2000 issue of Nibbling News – the bi-monthly magazine of the Rabbit and Rodent Enthusiasts Club – and was updated on 25th June 2002. It is copyright protected to the author and may not be reproduced in part or whole, without prior written permission from the author.