Lekcharoensuk C.
The Minnesota Urolith Center has analyzed uroliths from cats for almost 2 decades.
During this period it has been observed substantial changes in mineral composition.
In 1981, uroliths from 69 cats were analyzed: 78% cats had uroliths composed of magnesium ammonium phosphate(MAP) and only 1% had uroliths composed of calcium oxalate (CaOx).
In 1999 uroliths from 5091 cats were analyzed, 1647 (32%), had MAP uroliths, and 2817 (55%) had CaOx uroliths.
This observation suggests that differences in interrelated risks factors could be responsible ,at least in part ,for changes in prevalence of CaOx and MAP uroliths in cats.
The results of a previous study, also carried out at the Minnesota Urolith Center, had suggested that differences in race, sex, age and reproductive status did not affect the type of uroliths that the cat could develop, rather these factors influenced a subject’s propensity to develop uroliths in a general sense.
These findings support the prevailing opinion that diet-related treatment designed to minimize recurrence of MAP uroliths and urethral plugs has resulted in a reciprocal increase in the occurrence of CaOx uroliths.
Diet-induced urine acidification is an effective method of dissolving sterile MAP uroliths in cats and of preventing their formation, but diet-induced urine adicification promotes hypercalciuria and this is a risk factor for formation of CaOx uroliths.
Similarly a reduction in the dietary magnesium content to minimize formation of sterile MAP uroliths in cats has been suggested to increase the risk of CaOx urolith formation because urinary magnesium inhibits formation of CaOx crystals in human and rats.
However, a cause-and-effect relationship between dietary factors and the increase in the occurrence of CaOx uroliths and the decrease in the occurrence of MAP uroliths in cats has not yet been documented.
The purpose of this study was to identify dietary factors associated with changes in urolith’s composition.
Case cats consisted of 2 groups of cats reciding in the USA and Canada, all uroliths from both groups of cats had been summitted to the Minnesota Urolith Center for analysis.
A control cats group has been created with cats with no lower urinary tract disease and has been evaluated at the same veterinary hospitals as case cats.
At the end of the study groups of cats were composed: 173 cats with CaOx, 290 cats with MAP uroliths and 827 cats with no lower urinary tract disease.
The cats that were included in the study had never had previous episodes of crystalluria or previous pathologies of the lower urinary tract, to avoid that recent or previous treatments could influence the result of the study.
In order to evaluate the effect of the diet in the long run, cats that have been using the same feed for less than 6 months have been excluded.
For each sample that was sent to the minnesota urolith center, a very detailed questionnaire was delivered to the cat’s owner to collect information on the cat’s lifestyle, type of feed administered, quantity, frequency, duration of the meal, supplements and prizes administered, type of water administered, clinical history, pharmacological treatments.
Data collection revealed that cats that had calcium oxalate uroliths, compared to the control group, received diets with a significantly reduced protein, calcium, phosphorus, potassium and moisture content, and a significantly higher carbohydrate content.
This type of diet with a low content of proteins, sodium, potassium, and moisture and also formulated to maximize the acidification of the urinary pH have been shown to be responsible for an increased risk of developing calcium oxalate uroliths
At the same time, it has been shown that a decrease in the risk factor of the formation of calcium oxalate uroliths has been obtained by administering to fed cats containing moderate amounts of calcium, phosphorus or magnesium.
The cats that had MAP uroliths, compared to the control group, had been fed with significantly low fat, high carbohydrate, calcium, phosphorus, magnesium, sodium, potassium diets, and also with diets formulated to reduce the urine acidity.
No interference has been demonstrated on the formation of both types of uroliths due to the presence of high carbohydrate contents in the diet.
In light of these results, it emerges that diets specifically formulated to prevent MAP uroliths can represent a risk factor for the formation of calcium oxalate uroliths and vice versa.
Specifically on the basis of these results it is hypothesized that diets formulated with a significantly higher content of proteins, sodium, potassium, calcium, phosphorus, magnesium, and moisture and a normal content of carbohydrates, fats, fibers, and chloride can reduce the risk of formation of calcium oxalate uroliths in cats, also diets formulated to reduce the acidity of urine have been shown to have a beneficial effect on the health of these cats.
Diets formulated with a higher fat content, a normal carbohydrate, fiber, calcium, phosphorus, magnesium, sodium, chloride, and moisture content, and a lower protein and potassium content can decrease the risk of MAP urolith formation.
Furthermore, dietary changes aimed at increasing the acidity of the urine represent an additional positive factor in the reduction of the formation of MAP uroliths.
What emerges therefore from the results of this study is that, although risk factors may also be represented by the age, breed, reproductive status of the cat, feeding contributes significantly in conditioning the type of urolithiasis from which cats can be affected.