"A Basic Insight into the Common Canine & Feline Uroliths

"A Basic Insight into the Common Canine & Feline Uroliths

Health & Safety

There are several different types of urolith that can affect our dogs and cats (some breeds are inherently predisposed to various types). When urinary crystals accumulate they represent a dangerous condition as they can cause a urinary tract obstruction. Sometimes crystals can meld together to form large stones. Obstructions can be fatal if prompt treatment is not instigated due to the build-up of toxic waste.

Symptoms of urolithiasis may include :

  • Blood in the urine
  • Straining to pass urine; squatting and producing nothing or very little
  • Urinating in unusual places
  • Vocalisation and pain upon urination

The most common kindof urinary crystals that affect cats and dogs are called struvite (also known as triple phosphate or magnesium ammonium phosphate), although in the past twenty years calcium oxalate are catching up.

Struvite crystalsin dogs are almost alwayscausedbythe urease producing bacteria whichare responsible for urinary tract infections.In cats, the causes are more variable and although bacterial infection can sometimes be responsible, in many cases their formation is sterile (no-infectious) and influenced primarily by metabolic factors including the concentration of the urine, its pH (acidity/alkalinity) and excessive consumption of certain minerals and fibre.

Risk factors may include :

  • Obesity
  • Insufficient water intake
  • Stress / anxiety
  • A sedentary lifestyle

Neoplasia or trauma can also be causative or contributing factors. Some cats may suffer from idiopathic cystitis - which means cause unknown"" (this is more common in younger cats).


If a mild proliferation* of struvite crystals are diagnosed that are not causing any blockage, the usual course of actionis to treatany infection (if bacterial cystitis is present)with antibiotics, provide pain relief (urinary tract problems are typically VERY sore as you will knowif you have ever had cystitis)and nutritionally manage the condition using a prescription diet specially designed to dissolve the crystals. Always seek the professional opinion of your veterinary surgeon concerning the most appropriate diet for your cat or dog at this crucial first stage of treatment. Unless your pet refuses to eat the prescription diet, fails to digest it well, or the product contains ingredients which are known not to be appropriate due to a concurrent medical problem; it is usual to feed the prescribed diet for a least 6 weeks following the diagnosis.

Follow-up diagnostic tests will usually then be performed to assess progress. In some cases, your pet may be able to be weaned back onto regular pet food (within suitable nutritional parameters dependent upon the type of urolith), but in others, your vet may decide it is in the animal's best interest to continue with the prescription diet longer-term.

* Note: a very small number of struvite crystals in the urineis normal providing the animal is clinically well; if the animal is uncomfortable/infection is present then prompt treatment is obviously imperative.

If a blockage is present, catheterisation undergeneral anaestheticis requiredto flush through and dislodge the obstruction; or in very severe casessurgical intervention may be necessary. Animals requiring such treatment are usually hospitalised for several days so that the vet can monitor urination carefully. Antibiotic therapy, pain reliefand a prescription dissolution diet will again be necessary.

Diets for Struvite

  • Struvite crystals favour alkaline urine in which to form, so look for a product that promotes acidic urine.
  • Look for a product that has restricted levels of calcium, phosphorous and magnesium.
  • Diets that acidify the urine should not be given in conjunction with urinary acidifying drugs.
  • Some dissolution diets are high in sodium and designed for short term feeding rather than longer term.

Susceptible cat breeds: These may include the Himalayan, Ragdoll and Chartreux.
Susceptible dog breeds: Including the Miniature Schnauzer, Shih Tzu, Miniature Poodle, Cocker spaniel and Lhasa Apso.

Diets for Calcium Oxalate

  • Look for restricted, but not overly low levels of calcium. Very low levels can actually cause oxalate in the diet to be absorbed at even greater amounts since calciumcan bind to oxalate in the gut and prevent its systemic absorption.
  • Avoid oxalate rich ingredients, which include most fruits, green leafy veg, wheat and oats. Do bear in mind though that much of the oxalate in a pet’s body is not from the diet directly but from the natural processing of other nutrients.
  • It was thought that reducing the protein intake to promote a more alkaline urine could be beneficial but growing evidence suggests this is not likely to be the case.

Susceptible cat breeds: Burmese, Himalayan and Persian.
Susceptible dog breeds: Miniature Schnauzer, Yorkshire Terrier, Lhasa Apso and Miniature Poodle.

Diets for Urate

  • Unfortunately the only truly low purine food which would be suitable as a protein source for dogs is egg which does prove quite limiting; sometimes only a prescription diet will be able to meet the dog’s special requirements.
  • Foods which are high in purines and are to be avoided are: organ meats/offal (e.g. kidney, liver, heart, brain), game meats (e.g. venison, duck and goose), tinned fish ~ sardines, pilchards and mackerel (also mussels and scallops although I have never heard of people feeding these to their dogs!), cauliflower, mushrooms, peas, spinach, legumes, gravies and yeast.
  • Drugs such as cyclosporine increase uric acid levels in the urine. If a dogalready had the genetic mutation whereby the liver cells are unable to convert uric acid to allantoinit may be a causative factor in urate formation.
  • Allopurinol may be used to treat this condition in conjunction with an appropriate diet.

Susceptible breeds: Dalmatians, English Bulldogs and dogs with congenital portosystemic vascular shunts.

General Diet & Management Tips for Good Urinary Tract Health

  • Look for higher levels of Omega-3 DHA and EPA for their anti-inflammatory properties.
  • Look for products that contain cranberry, which contains a sugar substance (D-mannose), that has the special ability of being able to prevent harmful bacteria from sticking to the mucosal walls. Cranberry also contains arbutin, which is effective against certain bacteria and fungi, including Candida. By limiting these harmful bacteria, conditions such as cystitis may beless likely to affect the pet. Cranberry's antioxidant properties may also help to safeguard against the potentially harmful effects of free radicals. It also has antiviral properties.
  • Feed three smaller meals per day rather than one or two larger ones - this gives the gut less work to do at any one time, keeps the digestive enzymes ticking over nicely and ensures that maximum benefit is derived from the nutrients in the food. This is a good idea for any pet with a medical condition. If life is made as easy as possible for the digestion, the immune system can concentrate on its proper job of protecting the body, and this will have a knock-on positive effect on the other tissues, organs and vital systems of the body.
  • Ensure adequate fluid intake. Wet food, or a proportion of wet food may be beneficial for dogs and cats who are at risk of urinary tract infections and uroliths. Some dry foods can be fed soaked to increase their moisture content. Another suggestion is to purchase a pet water fountain which encourages greater water intake.
  • Ensure thatthe animalis kept at a healthy weight to avoid additional pressures onthe vital organs and joints. Sedentary or overweight cats and dogs are at a greater risk of a recurrence of crystals.
  • Look for foods that contain highly digestibleproteins which give the gut and immune systemmore nutritional value (and less waste).
  • Avoid mineral-rich or salty additions to the diet.
  • When comparing products, bear in mind that prescription diets declare their nutrient levels on a “dry matter” basis, whist regular commercial complete diets declare theirs on an “as fed” basis. Products with different moisture contents cannot be directly compared unless both are converted to DM basis. It is often helpful to calculate the intake of any nutrient in grams or milligrams per day based on the feeding volume. Your vet or pet food manufacturer will be able to help with a proper comparison and ensure the safest food is recommended in the light of the condition.

Unfortunately, it is very often the case thatcrystals will recur even if treated appropriately/a prescription dietor a good quality pet food is fed, so it'sextremely important to keep an extremely close eye on urination. If in doubt, always check with your vet. Please note that this article covers only three types of urolith; there are others that may also affect your cat or dog.


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