Stones & Sludge

Calcium is usually the main focus when discussing the causes of bladder stones and sludge in rabbits. While it is important to have a basic understanding of calcium metabolism in rabbits, it is also important to realize that other factors also play a role in the development of stones and sludge.

As Dr. Susan Brown writes in her “Bladder Stones in Rabbits” article, rabbits have a different way of processing calcium than other mammals. The amount of calcium that humans absorb depends upon what our body needs at the time. Excess calcium is then passed into the gastrointestinal tract and excreted as waste. However, in rabbits the calcium from their diet is absorbed whether they need it or not. The excess calcium (in the form of calcium carbonate) is mainly excreted via the kidneys.

When excreted, excess calcium carbonate gives the rabbit’s urine a white or cloudy appearance. You may notice a white chalky residue on the bottom of your rabbit’s cage after the urine has dried. This thin white chalky residue is not necessarily cause for alarm. However, it does indicate that your rabbit has more calcium in his diet than he needs, and you may need to make some dietary adjustments.

In some rabbits, the calcium carbonate in the urine binds together to form stones in the kidneys, bladder or ureters. What causes this mineral to bind together in some rabbits but not others is still unknown. Sludge, on the other hand, refers to a large number of small ‘crystals’ in the urine, which make the urine thick, gritty, sandy, or creamy and difficult or painful to pass.

Calcium is necessary for strong bones and teeth, so it should not be completely eliminated from your rabbit’s diet. Alfalfa hay has more than twice as much calcium as grass hay, such as timothy, so limiting or eliminating alfalfa hay from the diet is the most important step in reducing calcium in the diet. Next, choose a pellet that is low in calcium. Timothy-based pellets, which can be purchased through most vets, and some alfalfa-based brands are lower in calcium and recommended for rabbits prone to bladder stones or sludge.

Calcium metabolism in rabbits is not fully understood. As Laura Atkins and Susan Smith Ph.D. point out, there are many complex elements to consider when discussing calcium levels in vegetables. For example, if the calcium measurement was based on ‘dry weight’, the vegetable’s water content may not have been taken into consideration. Also, most vegetables contain oxalates, which bind to the calcium preventing it from being readily absorbed by the rabbit. Therefore, instead of avoiding all vegetables that are high in calcium to prevent stones and sludge, if your rabbit tolerates vegetables well, consider providing a variety of greens on a regular basis.

Other factors for developing stones:

As Dr. Brown also writes in her article, many rabbits have been fed high calcium diets for long periods of time yet never develop any urinary tract problems. Therefore, it’s important to consider that other factors may play a role in stone and sludge development as well. These include genetics, insufficient water intake, lack of exercise, infrequent urination, hind-end weakness (not able to fully empty bladder), kidney disease, bladder disease and urinary tract infection.

Unfortunately some of these factors, such as genetics, will be unknown to most owners and other factors cannot be prevented. Therefore it’s important to watch your rabbit closely to see if there are possible behaviours or dietary concerns that put him at higher risk.

Possible Signs of Urinary Problems:

• Urinating more frequently.

• Urinating outside the litter box (when the rabbit had previously good litter box habits), dribbling urine.

• Straining to urinate.

• Blood in urine (not red urine). Blood in the urine is difficult to see with the naked eye.

• Sand-like or gritty particles stuck to the rabbit’s underside.

• Loss of appetite, lethargy.

• Pain, sitting in ‘hunched up’ position

Monitor any changes and visit your veterinarian if you suspect a problem with stones, sludge or a urinary tract infection. Note: Calcium levels in the blood fluctuate depending on the calcium intake the day the blood was drawn, therefore a urine sample will provide a more accurate assessment of elevated calcium levels.


Jack’s story:

Jack was an overweight Polish dwarf who had been at my local shelter for seven months. He was brought in as a stray, therefore his age and medical history were unknown. Every time Jack was taken to the exercise area, he would immediately leave a large puddle of urine on the floor. Hmm… not the cleanest bunny, I thought.

But what bothered me most were the tiny hard feces in his cage. After reading the other volunteers’ and staff notes I learned Jack had been experiencing decreased fecal output for at least a month. The only ‘treatment’ he was receiving was a daily papaya tablet. I was really concerned for his health, so I adopted him.

Jack’s diet at the shelter had consisted of unlimited high fat, high calcium, low fibre pellets and alfalfa hay. I switched him to rationed high fibre pellets, and added numerous vegetables and timothy hay to his diet. He enjoyed the veggies, but wasn’t interested in the hay. I suspected painful molar spurs might have been causing his gastrointestinal slowdown. However a vet checkup ruled that out: his teeth were fine. The vet palpated his abdomen to check for a possible blockage, but that was fine as well.

I noticed Jack didn’t drink much water, so I continued to offer wet greens and tempt him with hay. Another trip to the vet brought subcutaneous fluids (under the skin) and an injection of Reglan (a motility drug), hoping that would jump-start his GI tract. But it didn’t help, so I requested an x-ray. This provided the answer: Jack had a very large bladder stone. It’s size indicated it had been a long-term problem.

Although I knew little of Jack’s medical history, I had witnessed a few factors that could have put him at a higher risk for stones. I knew his previous diet was high in calcium, he drank little water and had limited exercise. I also realized during the short time since Jack lived with me that he wasn’t the ‘unclean’ bunny I first thought. Actually he was too clean, he refused to urinate in his cage. Apparently the close proximity of bathroom and sleeping facilities was not an acceptable living arrangement for him. He would hold ‘it’ in until I opened his cage door and then he would make a beeline for the litter box a few feet away. To solve this problem I put a pen around his cage and litter box so he could use his ‘bathroom’ whenever he needed to.

Perhaps this odd behaviour, combined with a high calcium diet, little exercise and low water intake lead to this bladder stone. Whatever the cause, the only solution now was to have the stone surgically removed. But my vet wanted Jack to be eating and pooping a bit more before the surgery so the appointment was scheduled for early the following week.

That Sunday night Jack seemed uncomfortable. He sat in his litter box for long periods of time, often shifting and arching. I was very worried about him. I called the emergency clinic but the vet on call had little experience with rabbits. The next day I took him to my vet before the clinic even opened. Jack sat in his carrier looking alert and washing his face. He really didn’t ‘look’ like there was anything wrong with him. But seeing how stressed I was, and when I explained his behaviour from the night before, my vet decided to operate early that morning.

I soon got a call with bad news. The stone had left the bladder and lodged in the urethra behind the pubic bone. Not only was it inaccessible, it had torn his urethra and urine was leaking into his abdomen. My vet couldn’t help Jack further. I really felt like I had let Jack down, he must have been in a lot of pain.

I have two rabbits now that often have thick urine and are at a higher risk of developing sludge or stones. Many of their siblings have had problems with stones, so genetics may be a factor in their case. They drink very little water, but I’ve found that adding unsweetened pear or apple juice helps to make it more appealing. This trick increases their water consumption and helps to dilute their urine. Plus they eat a lot of vegetables.

I monitor their urine/fecal output regularly, and watch their behaviour for signs of pain.

It’s my hope that I can help prevent the painful bladder problems for them that I couldn’t for Jack.


Cocoa’s story:

Almost an inch in diameter, the ‘rock’ is what I call the single stone surgically removed from my boy’s bladder. Not surprisingly, it gets ‘oohs’ and ‘ahs’ from incredulous visitors, who like me, can’t believe it could have been inside a six and a half pound bunny.

When Cocoa was a yearling, I began noticing a frequent chalky residue in his litter box. But it wasn’t until I discovered the online resources concerning proper house rabbit care that I learned sludgy sediment and stones could scrape the bladder wall, making it vulnerable to infection. With this knowledge, I reduced Cocoa’s alfalfa based pellets: geared to quickly grow show rabbits, and rich in the calcium that can contribute to sludge.

During his fifth year, Cocoa began leaving puddles outside his litter box, digging with frustration in his litter, and constantly squatting without results – all classic signs of bladder infection. My vet, the only exotics specialist in my northern Ontario city of 130,000 people, diagnosed a bladder infection, along with sludge and a couple of small stones.

While treating the infection, we decided to administer daily subcutaneous fluids to flush the bladder and possibly pass the stones. This option best accommodated my small budget. I began further reducing calcium from Cocoa’s diet by gradually switching him from alfalfa pellets to Oxbow Hay’s timothy-based ‘Bunny Basics T’, reducing fresh foods higher in calcium, and encouraging increased fluid intake. A tablespoon-sized chunk of watermelon daily helped to accomplish this.

For two years following, Cocoa remained healthy and active, but then once again began showing signs of a bladder infection with blood in his urine and increasing incontinence. A medical exam revealed a single, large bladder stone had formed and would have to be removed. Since I was sure I would never be able to afford the costly procedure and the medications required, I was heart-broken. But miraculously, a number of people from the Internet rabbit group I frequent offered generously (around $1300) to pay for the surgery. Cocoa’s life was spared!

With only one exotics veterinarian to perform this operation, Cocoa’s surgery could not be set into her full schedule for two more weeks. With trying to keep his appetite up (fresh grass saved his life) and having to lay towels everywhere to absorb the constant peeing, I knew he couldn’t wait that long. After explaining our situation, the receptionist was kindly able to swap Cocoa’s time slot with a cat spay patient.

After a week of Baytril for his bladder infection, my almost eight-year-old boy, equipped with a bag lunch of veggies and his favourite fresh grass, went in early for bladder stone surgery. By afternoon, the vet informed me that he had come through the operation with flying colours. While visiting my groggy bunny in recovery, I coaxed him to eat greens from my hand. Cocoa would pause to stare absentmindedly, as if trying to remember what he had been doing, and then suddenly resume chewing. He felt sufficiently well to nudge me away when he had enough, so I left him surrounded by a smorgasbord of foods.

My vet said Cocoa’s bladder had been swollen due to the abrasive stone, so she had to sew together both the inside and outside layers of the bladder. The doctor had done an excellent job. His inverted abdominal stitches were seamless; he never once bothered to chew them. I, however, loved kissing his shaven, baby-pink tummy. Cocoa was given a painkiller for his first day home, but by the next day, he had already done a binky, contrary to doctor’s orders. How can you contain a happy, pain-free bunny? I also heard a fire hydrant-like stream of pee when he used his box: music to my ears!

Since Cocoa’s operation in May of 2002, I have again reduced his pellet intake to only a teaspoon per day. It was explained to me by a knowledgeable source that calcium content per dry weight in a pellet is more concentrated than the same amount in vegetables, which contain water. It is better, in my opinion, to give more juicy veggies than dry pellets. Soaking wet romaine, cilantro, (very limited) parsley, endive, celery, brussel sprouts, and fresh grass (in summer) are on Cocoa’s daily low calcium menu, along with his unlimited timothy hay. Nearing the first anniversary of his operation, Cocoa is still healthy and happy without any reoccurrence of his stone.

In retrospect, I believe the sludge and stone could have been prevented if he had been fed the timothy-based pellet at an earlier age.  Exercise also seems to be a crucial prevention factor: helping utilize the calcium within the body, and increasing bladder function. Cocoa is a fully freeroaming bun, but winters in northern Ontario are long and we all tend to become somewhat sedentary. During warmer temperatures, he goes outside regularly to romp.

My advice is to think about your rabbit’s diet early in life for prevention later. For not yet clearly understood reasons, individual rabbits metabolize calcium differently.  Most adult house rabbits don’t need the amounts of calcium in alfalfa-based pellets. Many rabbits have no problems with it, but it is something to consider.