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Urinary stones, also known as uroliths, are common in guinea pigs, most typically occurring in middle-aged to older pets. These stones are rock-hard masses of minerals that have crystallized in the urine. They can be found anywhere along the urinary tract, including:
- The kidneys (where urine is made)
- The ureters (which carry urine from the kidneys to the bladder)
- The bladder (where urine is stored)
- The urethra (which shuttles urine from the bladder to outside of the body).
Stones are most commonly found in the bladder, where they are called bladder stones, and in the urethra. If stones get stuck in the urethra or ureters, they can obstruct the flow of urine, resulting in a life-threatening situation.
If your guinea pig is showing any signs of a urinary problem, get them to a veterinarian as soon as possible.
We do not completely understand what causes urinary stones, but several risk factors may play a role. Because most guinea pigs’ urinary stones contain calcium, diets with lots of high-calcium foods such as alfalfa hay may be somewhat responsible. Other factors may include long-term dehydration, genetic predisposition, urinary tract infections, obesity, inactivity, poor hygiene, kidney disease and urine retention, or a neurologic disorder.
Why are urinary stones so common in guinea pigs?
Unlike most mammals, guinea pigs get rid of excess calcium mainly through their urine. Thus, their urine is concentrated with calcium, which may make them more prone to developing calcium-containing stones. Guinea pigs also normally produce alkaline urine, which can make them more likely to form stones, particularly in view of the aforementioned risk factors.
Signs will vary depending on the size and location of the stone(s), but sometimes guinea pigs won’t show any signs. Your guinea pig may have bloody urine and strain to urinate, which owners often incorrectly think is constipation. Other signs that indicate pain and discomfort include loudly grinding teeth, a hunched posture, and vocalizing while urinating. Your guinea pig may produce very little to no urine, stop eating and lose weight, and seem depressed and less active than usual. If you notice any of these signs, bring your guinea pig to a veterinarian as soon as possible.
For diagnosis, your veterinarian will use a history of your guinea pig’s problem, physical examination findings, and further tests, including X-rays. X-rays can confirm that your guinea pig has them and determine where they are. Your veterinarian may also take a urine sample to check for calcium-containing crystals and signs of a urinary tract infection, which as mentioned can occur with stones. They can also test the sample to confirm whether red urine really is due to blood because sometimes healthy guinea pigs can produce pigmented urine without any bleeding. Your veterinarian may also run blood tests to check on kidney function, look for other abnormalities, and assess overall health.
Your veterinarian may want to pursue some of many treatment options, depending on the size and location of the stone(s), your pet’s current status, and what is feasible for you. Surgery is considered the standard of care for large or painful stones. Bladder stones are removed through a procedure called a cystotomy, during which the bladder is cut open and the stones are taken out.
If stones are in the urethra, they can be flushed back into the bladder and removed during the same procedure. Your veterinarian will slide a flexible tube called a catheter into the urethra and pour fluid through it to put pressure on the stone to move, just like hosing rocks off a driveway. If the stone won’t budge, your veterinarian may need to cut open the urethra. Female guinea pigs have such short urethras that sometimes stones can be removed non-surgically using specialized equipment. If your guinea pig has stones in the kidneys or ureters, your veterinarian may recommend bringing them to a surgeon who has the equipment for these procedures.
After surgery, X-rays will be taken to ensure all the stones were removed. Your guinea pig will be given pain medication and fluids. If a urinary tract infection was found on the urine sample, antibiotics may be given. Your guinea pig will need to be hydrated and urinating on their own before being sent home with you.
Some non-surgical techniques may be recommended depending on the situation. If a stone is small (less than 5 millimeters), it could pass on its own. In these cases. Or in cases where surgery is not possible, conservative treatment, such as pain meds, fluids, antibiotics, and careful monitoring (periodic X-rays, checking for blood in the urine, etc.) may be options. Sometimes, a guinea pig won’t have developed stones yet but already has sludge in the bladder. Sludge is crystals in the urine before they form into stones. Sludge may be removed from the bladder through a process called bladder flushing, where your veterinarian pushes fluid through a catheter into the bladder, massages the bladder to mix the sludge and the fluid, then squeezes the bladder to push out the sludge mixture through the catheter. If this method is unsuccessful at removing all the sludge, a cystotomy may yet be necessary.
Even with successful treatment, stones commonly recur in guinea pigs, so it is important to take preventive measures after they are removed.
Generally, the prognosis is considered excellent for bladder stones or sludge, but not as good for stones in the urethra. The prognosis for a urinary obstruction is considered poor, but if diagnosed and managed quickly enough, treatment can be successful.
Nothing can 100% guarantee your guinea pig won’t get urinary stones. Nonetheless, the measures listed below may reduce the risk and be worth pursuing, especially if your guinea pig has already had a stone. Recurrence is common.
Diet: Because most urinary stones contain calcium, your guinea pig’s diet should have just the right amount of calcium: enough, but not too much. You can get this balance by avoiding high-calcium foods, such as alfalfa hay, kale, dandelion greens, and spinach. A guinea pig’s diet ideally consists of unlimited amounts of timothy hay, which is low in calcium, along with a smaller amount of timothy hay-based pellets and fresh, leafy green or colored vegetables.
Water: Because chronic dehydration is a risk factor, your guinea pig must stay hydrated. Provide water at all times through multiple sources. Giving your guinea pig wet vegetables and spraying veggies with water can also help.
Exercise: Your guinea pig should get sufficient exercise and play time. The activity may help keep the urine in the bladder moving so that crystals don’t settle and form into stones.
Cage hygiene: Your guinea pig’s living environment should be kept clean to prevent urinary tract infections.
Medications: Your veterinarian may recommend certain medications to reduce the risk of forming more stones. One possibility is potassium citrate; it is given by mouth and binds calcium in the urine, preventing it from crystallizing and coalescing into urinary stones. Some veterinarians may also suggest using a diuretic called hydrochlorothiazide. This drug, also given by mouth, increases urine volume, thus diluting calcium and potentially reducing the risk of forming stones. However, if you use this medication, you must make sure you have multiple sources of water available for your guinea pig at all times. It is necessary to prevent dehydration from so much water being lost in the urine.
Urinary stones are a common and potentially life-threatening problem in guinea pigs. Learn to recognize the signs and bring your guinea pig to a veterinarian as soon as possible if you notice anything wrong.