A not infrequently seen clinical problem in cats is that of stones within the urinary tract. These can be found (most commonly) in the bladder, although they are sometimes also found in the kidneys, ureters and urethra as well. Depending on where the stones are found, clinical symptoms can, of course, be quite varied and broad ranging.
Different types of urinary stones exist, and some are more commonly seen than others. Broadly speaking in terms of management of these stones, there is dietary therapy (in the form of “dissolution” diets), or surgical management for those stones which are not amenable to dissolving (with diet) and therefore require a surgical approach to remove them instead. In this article we will discuss the diets for urinary stones in cats: when are they indicated, how can they be used and when is it not suitable to employ them.
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Struvite stones
Historically perhaps the most commonly seen bladder stones in cats were struvite stones. These can be preceded by struvite crystals (microscopic) which, over time, amalgamate into larger discrete stones. The composition of these stones is made up of 3 “ingredients”- phosphate, magnesium and ammonium. Although the mechanisms that lead to stone formation are not wholly understood. What is clear is that in clinically affected cats, high concentrations of the constituent stone forming substances exist within the urine, transit time within the urinary tract is reduced, and other factors, such as an alkaline urine, favour their formation. Urinary tract infections may also be a factor in the development of struvite stones.
To treat struvite stones, struvite “dissolution” diets are available
These diets aim to reduce the urinary pH (make it more acidic); increase the dilution of the urine (make it less concentrated); and also “under-saturate” the urine with the component mineral ingredients. These diets, assuming 100% of the stones are indeed struvite, typically work well, although there can be a considerable range in the length of time for them to act and complete their desired effect. If infection is associated with the stones, this also will need to be adequately treated.
Struvite dissolution diets are produced by a range of pet food manufacturers and come in wet and dry formulation options. However the wet foods will serve to have an enhanced beneficial effect, by helping to dilute the crystals, slowing re-forming of the stones. As prescription diets, they should only be fed to your cat once your vet has informed you that it would be appropriate to do so. In some individual cats, there can also be an association between cats showing urinary tract disease and environmental stressors. So, in addition, some of these formulated diets will contain extra natural ingredients. These ingredients can help to provide reassurance to your cat, reduce stress and anxiety levels and promote feelings of well-being.
How to use
If your vet has recommended a struvite dissolution diet for your cat, it is important to introduce this gradually, over at least one week and preferably longer. Your cat will need to be on this food for anything up to a number of weeks and the success rate of transitioning to this food will be indirectly correlated to the speed at which you make that change. To put it another way, your cat will likely approve of the food for a longer period of time, the slower you have changed them over to it!
Your vet will need to periodically reassess the response to treatment by use of regular urinalysis (urine samples) and also imaging. Ultrasound or radiography (x-rays) can both be used to make sequential assessments of treatment progress and success.
Diets are not suitable for…
There are some other types of urinary stones that can form in cats. And these are unfortunately not necessarily amenable to dietary dissolution.
The “rising star” of the cat stone world, over the past decade or so, has been the calcium set of stones, calcium oxalate in particular. In stark contrast to struvite stones, these cannot be dissolved with a diet. Depending on their location (and associated clinical symptoms), they may need to be surgically removed, or another technique employed.
The calcium set of stones differ from the struvite, in that they form in acidic urine. Cats can be predisposed to them forming for a number of different reasons. These stones can also be associated with the poorly understood feline “idiopathic hypercalcaemia (IHC)” condition. Whilst a diet will not specifically dissolve calcium stones, for the longer-term, to attempt preventative management, a specific urinary diet may aim to keep the urine pH neutral (as it should be) and promote a high “turnover” of urine (again, through promoting water intake) – both of which are likely to be beneficial. Cats suffering from IHC may also undergo specific individualised dietary therapy, aimed at managing this underlying condition.
The other types of feline urinary stones, urates and cystine, are exceptionally rare. The former being seen in cats with congenital or acquired liver conditions, or perhaps in some certain exotic breeds of cats. Dietary therapy exists for urate stones not associated with liver disease and is similar to that for cystine stones too.
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