Urolithiasis

Urolithiasis is the formation of calculi in the urinary tract, also called kidney and bladder calculi or stones, or urinary tract stones. The stones are rock hard crystal aggregations of all shapes and sizes. Sludge is the name given to the thick, almost toothpaste consistency deposit that can build up in the guinea pigs bladder or kidneys and is a separate condition to stones, but the two conditions may be related.

As for all mammals, calcium is very important for guinea pigs; they need it to form strong and healthy bones and teeth (and so to prevent dental problems and osteoporosis). Just as too little can cause problems, so can excess quantities, and although calcium consumption isn’t believed to be the main factor responsible for the development of calculi (stones), it is thought that it is likely to play some part, so getting your guinea pig’s calcium intake correct may help to prevent future problems.

A guinea pig fed a good balanced diet shouldn’t be calcium deficient and won’t need a calcium or mineral supplement.

Guinea pigs have an unusual calcium metabolism. In most mammals, the amount of calcium absorbed from the diet is regulated at gut level by the parathyroid hormone (PTH), but guinea pigs predominantly absorb calcium in proportion to what is present in their diet, whether or not they require it. Meaning that whatever amount of calcium a guinea pig has in their diet, they will absorb it all. This evolutionary trait stems from wild guinea pigs and the sparse diet they often eat. During times of the year when vegetation is low in minerals, guinea pigs need to be able to absorb all the useful nutrients and not waste any; our pet guinea pigs do not have this problem as their diet is stable all year round. Any excess calcium that is absorbed into the bloodstream from the gut is excreted through the urinary tract, where it may be deposited and form calculi/sludge. Guinea pigs can form solid calcifications in their kidneys, ureters, bladder or urethra, as well as depositing thick calcium sludge in their kidneys or bladder.

Calculi

One or more stones may develop, with or without sludge being present. Symptoms of calculi include loss of appetite, loud painful teeth grinding, hunched posture, lethargy, unwillingness to move, pressing abdomen on the ground, loss of litter training, blood in the urine, perineal scalding and straining to urinate. One or more symptoms may appear gradually or have a sudden onset and be intermittent.

A blood test is useful for determining kidney function and calcium levels in the blood. A urine test should also be taken to see if calcium crystals and/or a urinary infection (cystitis) are present.

Sludge

Guinea pigs suffering from sludge may display any of the symptoms described above for calculi, as well as passing thick, white, gritty urine that in severe cases will become semi-solid when passed. White or sludgy urine on their own are common in guinea pigs and often occur after the guinea pig has eaten high calcium foods. They aren’t necessarily indicative of sludge within the urinary tract; this must be confirmed. Diagnosis is the same as that of calculi; as the sludge is made of calcium, it too will show up on an x-ray or ultrasound as a mass.

As some guinea pigs exhibiting no clinical symptoms, can upon investigation, be found to have some degree of sludge in their bladder or kidneys, treatment to flush the sludge from the bladder, is only necessary if the sludge seems to be causing the guinea pig problems. Sludge in the kidneys is more difficult to eliminate, although kidneys can be flushed, and flushings may be sufficient to return the kidneys to an acceptable working capacity, it is unlikely to clear all of the sludge.

Treatment depends upon the location of the calcification/s. The deposit of calcium salts (calcifications) show up on x-rays and ultrasound scans, as the calcium content makes them radiopaque (light in color). Calcifications detected in the bladder, ureters or urethra should be surgically removed once the guinea pig’s condition has been stabilized.

Guinea pigs suffering from calculi are often in a lot of pain and as a result will not eat or drink, subsequently being dehydrated and necessitating fluid therapy, gastrointestinal support and pain relief prior to surgery. Currently there is no known method of breaking up guinea pig calculi and it is rare for the guinea pig to pass them naturally, due to their often-jagged texture and size to which they can grow. Ureteral calculi may cause enlargement of the kidney (hydronephrosis) due to obstructed urine flow from the kidney to the bladder. With such a situation, once the guinea pig is stabilized, prompt surgical intervention to remove the calculi is vital to avoid irreparable damage.

Guinea pigs presenting with calculi in both kidneys, displaying clinical symptoms have a guarded to poor prognosis. Surgically removing calculi from the kidney is extremely hazardous, and for these cases management may be the only treatment option, with their quality of life paramount. If calculi are only located in one kidney, it may be possible to remove the affected kidney, as the remaining kidney should have adequate function to keep the guinea pig alive. However, if the remaining kidney becomes unable to work to near full capacity, the guinea pig’s prognosis is extremely grave.

Calcium consumption isn’t believed to be the main factor responsible for calculi/sludge development, which is why solely reducing the calcium intake often doesn’t prevent the problem from reoccurring. Other possible reasons include the following:

A low water intake

This is suspected to be one of the most important factors leading to the formation of urinary calculi. Less urine is produced with a low water intake and calcium precipitates out when urine is saturated with calcium. To rectify this problem, you must increase the guinea pig’s fluid intake, which can be achieved by:

• Adding apple juice or other sweet flavoring to their water (take care not to put them off drinking as a ‘strange’ smell or taste to the water may have this effect).
• Adding water onto the fresh vegetables by spraying a mist of water.
• If neither of the above works, syringe-feeding fluids or fluid administration by your veterinarian may be the only way of increasing the fluid intake if you are unable to achieve it through dietary modifications.

Guinea pig is overweight

Overweight guinea pigs may be physically unable to completely empty their bladder, due to weak muscle tone, or adopt the correct position for urination, which will give any calcium in the urine a chance to settle in the bladder. Make sure your guinea pig is not overweight, and if they are, speak to your veterinary practice to arrange an appointment with your veterinarian or veterinary nurse to implement a safe weight loss programme.

Kidney damage

The guinea pig’s kidneys may be unable to manage the amount of calcium, which they are required to process. Kidney damage only shows up on blood tests when at least 75% of kidney function is lost.

Litter training

Most guinea pigs will only urinate in a select number of places. If the guinea pig is unable to reach these places, ie no litter tray in pen, it may wait until it can urinate in its desired area, so always ensure your guinea pig is able to reach its toilet areas.

Urine retention

Urine retention can be caused by osteoarthritis, pododermatitis and spinal problems, these will need corrective measures implemented, such as weight loss, analgesia and adapted housing so the guinea pig isn’t painful or their mobility impaired so they can access litter trays and adopt the correct position for frequent urination.

Oxalate

Some green foods are high in oxalate (spinach, parsley, spring greens, etc). Oxalates should be metabolized by bacteria in the gut, but if there aren’t enough oxalate-eating bacteria, the oxalate will be absorbed rather than broken down and excreted via the kidneys, with calcium hitching a ride.

Genetics

Even after all the above have been explored and ruled out, and the guinea pig’s access to calcium restricted, if the guinea pig still continues to produce calculi/sludge, then a genetic reason should be considered. Some guinea pigs may fundamentally be “stone/sludge formers” and whilst a genetic reason can’t be ruled out, guinea pigs affected with urolithiasis problems should never be bred from.

Fruit and vegetable can be grouped into good, moderate and poor calcium providers. However, it is important to remember that the vast majority of any fresh food is water, and therefore even the fresh foods higher in calcium are still suitable to feed. Fruits must only be fed as very occasional treats and the main bulk of a guinea pigs fresh food allowance should be greens and herbs:

Good calcium providers

• Kale.
• Spinach.
• Parsley.
• Watercress.
• Mint.
• Spring greens.

Moderate calcium providers

• Cabbage.
• Broccoli.
• Celery.

Poor calcium providers

• Brussel sprouts.
• Carrots.
• Cauliflower.
• Apple.
• Apricot.
• Banana.
• Grapes.
• Pears.
• Pineapple.
• Strawberries.

Alfalfa hay contains approximately 1.5% calcium, compared with 0.4-0.8% calcium in grass hays. Nutritional values for hay and fresh foods vary depending upon the soil the product was grown in, the time of year it was harvested and other conditions that affect nutritional values.

Once the initial condition has been treated, attention must focus on trying to prevent reoccurrence of the condition, but even then, there is a possibility of further calculi or sludge forming, particularly if the guinea pig still has sludge within their kidneys or bladder. The most successful approach to preventing reoccurrence of calculi or sludge seems to be by adopting a multi-tiered approach and tackling several possible factors concurrently:

• Pellets should be excluded from the diet or fed in tiny proportions as an occasional treat. Any alfalfa-based foods and calcium/mineral supplements should be permanently removed from the diet.
• Feed a good amount of fresh food daily (15-20% of the guinea pig’s diet should be fresh food), with the rest consisting of hay/grass. This not only lowers the calcium intake but also increases water consumption, which seems to be critical for guinea pigs with urolithiasis.
• Offer grass hays (timothy, fescues, ryegrass, bromegrass or orchard grass) ad lib.
• Ensure your guinea pig isn’t overweight and gets plenty of exercise.
• Always ensure your guinea pig can reach its toilet areas and has several of these.
• Implement careful monitoring, usually consisting of blood and urine tests, as well as periodic x-rays/ultrasounds to monitor the condition and detect any reformation of calculi/sludge early on.

Changes in diet should be done over at least a couple of weeks to prevent digestive upsets. Introduce one new food at a time and if it seems to upset the guinea pig in the next 24-48 h exclude it from the diet. Try to feed smaller quantities of numerous different foods, rather than larger quantities of a few foods. This gives the guinea pig a variety, and also helps to achieve a balance of other minerals.

The vast majority of guinea pigs on a hay and veggie diet manage fine and get through a mound of fresh food their own body size daily. Hay and water must always be available.