Feline struvite urolithiasis: factors affecting urine pH may be more important than magnesium levels in food

Eighteen male cats were fed either a canned complete diet or a commercially available dry pelleted diet or the same dry diet containing 1.6 per cent ammonium chloride. The daily food and water intake of four of these cats was measured. Urine samples were taken at random and the pH and the presence of struvite crystals in their sediment estimated. In some samples in which the pH was less than 7.0, and struvite crystals were absent, the pH was increased to 7.0 and any sediment was examined for struvite. No spontaneous struvite was seen in urine samples (pH 5.8) from cats fed the canned complete diet but when its pH was raised to 7.0, 46 per cent of these samples showed struvite. Cats fed the dry pelleted diet had urine of higher pH (7.55) and 78 per cent of the samples contained struvite crystals. Cats fed this diet supplemented with ammonium chloride had a urine pH of 5.97 and only 9 per cent contained struvite crystals but when the pH was adjusted to 7.0 all the samples showed struvite crystals. Energy intake was similar on all three diets but the intake of dry matter was greater on the dry diets. Liquid water intake was greater on the dry diets but total water intake was greatest on the canned complete diet. The intake of magnesium, calcium and phosphate was greater on the dry diets. It is concluded that urine pH is a more important controller of struvite precipitation than mineral intake.     

Effect of magnesium-deficient diet on serum and urine magnesium concentrations in healthy cats.

OBJECTIVE: To evaluate the efficacy of using serum total and ionized magnesium (Mg) concentrations and urine Mg concentrations to identify Mg deficiency in cats. ANIMALS: 6 healthy castrated male cats. PROCEDURE: A Mg-replete diet was fed for 37 days, followed by a Mg-deficient diet for 37 days. On days 1, 3, and 7 of the last week of each diet, serum ionized and total Mg concentrations were determined; in addition, urine Mg concentration was determined each day of the last week. Serum total and ionized Mg concentrations were compared with urine Mg concentration, amount of Mg excreted during 24 hours (24-hour urine Mg excretion), ratio of urine Mg concentration to urine creatinine concentration (Umg:Ucr), and urinary fractional excretion of Mg (FEmg) to determine which variable best predicted Mg status. RESULTS: Cats fed Mg-deficient diets had significantly lower serum total and ionized Mg concentrations and 24-hour urine Mg excretion values, compared with cats fed Mg-replete diets. Serum total Mg concentration was the best predictor of Mg status. Twenty-four-hour urine Mg excretion was a repeatable, reliable measurement and had the best correlation with serum total Mg concentration. Serum total Mg concentration also correlated with urine Mg concentration, Umg:Ucr, and FEmg. CONCLUSIONS AND CLINICAL RELEVANCE: Serum total and ionized Mg concentrations can be used to identify cats with dietary-induced Mg deficiencies. Twenty-four-hour urine Mg excretion and urine Mg concentration correlated best with serum total Mg concentration and, therefore, may be the most useful urine variables for identifying Mg deficiency.     

Substitution of dietary calcium chloride for calcium carbonate reduces urinary ph and urinary phosphorus excretion in adult cats

Summary

In a 4×4‐vvk cross‐over study, eight adult cats were given four moist diets containing identical amounts of calcium (13.9 mmol/MJ) but with different ratios of calcium carbonate to calcium chloride, the calcium salts providing half of the total dietary calcium. Increasing amounts of calcium chloride were substituted for equimolar amounts of calcium carbonate. Higher intakes of calcium chloride caused significantly lower pH values in postprandial and 24‐h urine samples. The urinary excretion of ammonium and titratable acid rose with increasing calcium chloride intake. The urinary concentrations of calcium and magnesium were not affected by the type of calcium salt, but the urinary excretion and concentration of phosphorus were significantly depressed when the amount of calcium chloride in the diet was increased. The results are discussed in the context of dietary prevention of and therapy for struvite urolithiasis in cats.     

Risk factors and clinical presentation of cats with feline idiopathic cystitis

Feline idiopathic cystitis (FIC) is the most common cause of feline lower urinary tract disease (FLUTD). This retrospective, case-controlled study evaluated possible risk factors associated with FIC and compared different clinical presentations in 64 cats with FIC. Several risk factors known to be involved in FLUTD were identified as playing a role in FIC. Of the stressful situations considered, most did not occur with increased frequency in cats with FIC compared to controls, except for a house move. The presence of pyuria, haematuria and an increased urine protein:creatinine ratio were significantly higher in obstructed males compared with non-obstructed males. An obstruction was significantly more likely in cats with struvite crystalluria compared with cats without struvite crystalluria. These findings suggest that urethral plugs might be an important cause or contributing factor of obstruction in FIC. Episodes of FIC seem to occur mainly in susceptible cats in combination with a deficient environment.     

Nutrition and aspects of feline lower urinary tract disease

Important causes of feline lower urinary tract disease (LUTD) that have been identified include urolithiasis and the formation of urethral plugs. In many cases, however, no specific cause of disease may be evident. Clinical studies in cats with apparently ‘idiopathic’ feline LUTD have suggested that some cases may respond to dietary modification, with diets designed to acidify urine, provide a good urine volume and relatively restricted magnesium intake. Nutritional research has predominantly focused on factors that may contribute to the formation of struvite uroliths, and has resulted in the development of specific recommendations for the management and subsequent prevention of recurrence of this condition. Urethral plugs have been less well studied, although recent clinical observations provide evidence that dietary modification may be of value in preventing their recurrence.     

Comparison of corn gluten meal and meat meal as a protein source in dry foods formulated for cats

OBJECTIVE: To compare the nutritional value of corn gluten meal (CGM) and meat meal (MM) as a dietary source of protein in dry food formulated for adult cats. ANIMALS: 8 healthy adult cats (4 males and 4 females). PROCEDURE: Diets containing CGM or MM as the main protein source were each fed for a 3-week period in a crossover study. Digestibility and nutritional balance experiments were conducted during the last 7 days of each period. Furthermore, freshly voided urine was obtained to measure urinary pH, struvite crystals, and sediment concentrations. RESULTS: Daily food intake and dry-matter digestibility were significantly higher for the MM diet. Fecal moisture content also was higher for the MM diet. Apparent nitrogen (N) absorption and N retention were higher for the MM diet, even when values were expressed as a percentage to account for differences in N intake. Urinary pH, struvite activity product, number of struvite crystals in urine, and urinary sediment concentrations were not different between diets. Retention of calcium, phosphorus, and magnesium was lower for the CGM diet, and cats lost body calcium and magnesium when fed the CGM diet. CONCLUSIONS AND CLINICAL RELEVANCE: Meat meal was superior to CGM as a protein source in dry foods formulated for cats, because dry-matter digestibility and N utilization were higher for the MM diet. In addition, net loss of body calcium and magnesium for the CGM diet suggests that mineral requirements increase when CGM is used as a protein source.     

Perineal urethrostomy versus dietary management in prevention of recurrent lower urinary tract disease

The frequency and cause of recurrent lower urinary tract disease was compared prospectively in three groups of 10 male cats during a one year period following correction of obstructive urethropathy caused by matrix-crystalline plugs. One group of cats was managed by perineal urethrostomy, one group with a calculolytic diet, and the third group by perineal urethrostomy and the calculolytic diet. Ten episodes of bacterial urinary tract infection developed in five of 10 cats with perineal urethrostomies; six episodes of bacterial urinary tract infection developed in four of 10 cats with perineal urethrostomies and consuming the calculolytic diet. Bacterial urinary tract infections were not observed in cats managed only with the calculolytic diet. Staphylococcal-induced struvite urocystoliths developed in two cats with perineal urethrostomies. Vesicourachal diverticula detected in nine cats at the time of diagnosis of urethral obstruction healed spontaneously following restoration of urethral patency and remission of clinical signs. Transient microscopic haematuria was observed in approximately 25 per cent of the cats in all three treatment groups during the one year study. Results of this study confirm the effectiveness of dietary management in prevention of recurrent urethral obstruction caused by struvite-containing urethral precipitates, and verify that recurrent signs of lower urinary tract disease in cats may be caused by agents that are different from those that initiate the problem. They also confirm that perineal urethrostomies predispose cats to recurrent ascending bacterial urinary tract infections.     

Feline struvite urolithiasis: fasting reduced the effectiveness of a urinary acidifier (ammonium chloride) and increased the intake of a low magnesium diet

In three separate experiments nine male cats were fed either a canned complete diet or a commercially available dry pelleted diet or the same dry diet containing 1.6 per cent ammonium chloride for seven days and then fasted for 20 hours. Then ad libitum feeding was continued and urine samples were taken at four-hour intervals for 12 hours and a final sample 12 hours later. Urine pH and the presence of struvite crystals in urine sediment were evaluated. The food and water intake of four of the nine cats was measured at the time of urine collection. After the fast, urine pH was raised, even after feeding the dry diet supplemented with ammonium chloride. A post prandial rise in urine pH was also seen on all three diets. After feeding the dry diet the postprandial peak pH was 7.97 and struvite occurred spontaneously. Urine pH after feeding the dry diet supplemented with ammonium chloride peaked at 7.75 then fell to 6.1 12 hours after the start of feeding. Struvite occurred spontaneously at all times until the pH reached 6.1 but when the pH of urine was raised to 7.0 the struvite crystallised. Urine pH on the canned complete diet peaked at 6.8 then fell to 5.8; struvite did not occur spontaneously but when urine pH was raised to 7.0 struvite crystallised except at the eighth and 12th hour sampling. These data show that fasting initiates a post prandial rise in urine pH and struvite crystalluria even when a normally effective urinary acidifier is used.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dietary treatment of progressive feline struvite crystalluria

Eight cats were fed a dry commercial cat food and after six months developed urinary struvite crystalluria with alkaline urine. The animals were subsequently divided into two groups and fed either a dry or a canned struvite calculolytic diet. The crystalluria was reduced after five to six weeks with both treatment diets. Decreased crystalluria coincided with a reduction in urinary pH and an increased titratable acidity. The highest food acid load, determined by the lowest undetermined anion, was found with the dry diet and resulted in the highest renal hydrogen excretion, measured as net acid excretion.     

Feline urological syndrome (FUS) - theory and practice

Feline urological syndrome (FUS, urolithiasis, feline urethral obstruction, ‘blocked cat’) is the most important condition of the lower urinary tract of the cat, both because of its frequency of occurrence and the immediately serious nature of some facets of the clinical condition. It is also an enigmatic disease on which much clinical and research effort has been expended, but about which much remains to be understood. Problems include those of definition, of aetiology and of pathogenesis, and each are of practical as well as theoretical importance. The first, in the absence of a single diagnostic criterion, is clearly essential as a basis for clinical management. Considerable efforts have been made to define a single cause or aetiology but have not proved helpful and it is now clear that the development of FUS may be related to a number of factors. Understanding of the pathogenesis of FUS remains patchy, for while the metabolic consequences of urethral obstruction are relatively well understood, little is known of the earlier, pre-clinical stages of the disease where the role of struvite crystals and the colloid matrix of the obstructing material remains unclear. These aspects, and their relevance in the management of clinical FUS will be discussed.     

Food and water intake and urine composition in cats: influence of continuous versus periodic feeding

Twenty healthy, noncastrated, adult male cats had periodic (11 am to 12 am) or continuous (24 hours daily) access to food. With periodic feeding, cats ate less food, drank less water, and produced less urine than when food was available continuously. The composition of urine obtained by cystocentesis at 7:30 am, 3:30 pm, and 10 pm was influenced somewhat by feeding pattern. With periodic feeding, urine pH was lower at 7:30 am and higher at 3:30 pm than it was with continuous feeding. Most mineral concentrations and urine osmolality-specific gravity did not differ with the different feeding schedules. However, when periodic feeding was used, concentrations of magnesium and phosphorus in urine were as high or higher preprandially (7:30 am) than postprandially (3:30 pm). Frequency of urination per 24 hours was not influenced by the feeding schedule, but the time that urination occurred during the 24-hour period was somewhat different. An experimental, high magnesium diet fed to the cats for 200 days caused urethral obstruction in 7 of 10 cats fed periodically and in 7 of 10 cats fed continuously. Cats with obstruction had urinary mineral concentrations similar to concentrations in cats without obstruction, indicating that urinary mineral concentration may not be the only factor relevant to the process of obstruction. Necropsy findings and histologic evaluation of tissues from the cats indicated incidental lesions or abnormalities caused by urethral obstruction, but did not indicate anatomic abnormalities that would have predisposed the cats to obstruction.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of food intake on urine pH in cats

Ninety adult cats were fed an experimental canned meat-based cat food at levels necessary to maintain weight for 11 days. On the 12th day the cats were split into six groups of 15 cats each and fed 0, 20, 40, 60, 80 or 100 per cent of their previous food allotment. Four hours after the food was offered a urine sample was obtained via cysto-centesis. The pH of the urine sample was determined and the sample microscopically evaluated for the presence of struvite crystals. Post prandial urine pH was found to be a linear function of the amount of food consumed: (urine pH = 6–15 + [food intake (g) × 0–015]; P = 0-000). The presence of struvite crystals was dependent on urine pH while amorphous crystals were not. These data suggest that ad libitum feeding (nibble eating) may be beneficial in the management of feline struvite urolithiasis by reducing the magnitude of the post prandial alkaline tide. It also supports the suggestion that struvite crystal formation is largely a function of urinary pH.     

Feline struvite crystalluria: a comparison of some commercially available dry cat diets in New Zealand

Thirteen adult cats were each fed consecutively five test diets: firstly a complete canned diet, and then four commercially available dry cat diets (New Formula Biscats, Cat Chow, Go-Cat and Whiskettes) for 7,13, 5, 4 and 4 weeks respectively. Urine samples were tested for pH and presence of struvite crystals. Body weight was recorded weekly. Urine pH was ranked from acid to alkaline as follows: Whiskettes (pH 5.8), canned diet (pH 5.9), Biscats (pH 6.1), Cat Chow (pH 6.45) and Go-Cat (pH 6.5). The pH of urine when cats were fed Whiskettes, Biscats and canned diet was not significantly different. Biscats produced a urine pH significantly higher than Whiskettes but, in each case, these three diets produced a significantly lower urine pH than Cat Chow and Go-Cat. Struvite crystals occurred spontaneously in 9% of urine samples from cats when fed Whiskettes and Biscats, 71% when fed Cat Chow and 38% when fed Go-Cat: spontaneous struvite was not seen in any cat fed CX9. Haematuria was seen in 2.9% (2/69) urine samples from cats fed Cat Chow. One tom cat had a blocked urethra after 24 days on Go-Cat. No abnormalities were observed in any cat when fed canned diet, Biscats or Whiskettes. It was concluded that of the four dry cat diets tested only Biscats and Whiskettes produce urine with an acceptably low rate of spontaneous struvite crystalluria.     

The effect of urine acidification on calcium oxalate relative supersaturation in cats

There is an apparent reciprocal relationship between magnesium ammonium phosphate (MAP, struvite) and calcium oxalate (CaOx) urolithiasis incidence rate in cats. The number of struvite uroliths submitted for analysis over the past 35 years has been decreasing, with an increase in CaOx urolith submissions. Commercial diets aimed to dissolve struvite uroliths are typically acidified, and it has been suggested that dietary acidification increases urinary calcium excretion and the risk of CaOx crystallization. The objective of this study was to assess the effect of urine acidification on the relative supersaturation (RSS) of CaOx in cats, as a representation of crystallization risk. Four diets were extruded to contain identical nutrient contents, but with gradual acidification (0, 0.6, 1.3 and 1.9% sodium bisulphate substituted sodium chloride in diets A, B, C and D respectively). Thirteen adult cats were fed each diet sequentially for a minimum of 10 days. Average urine pH was 6.4, 6.2, 6.0 and 5.9 on diets A, B, C and D respectively (p < 0.0001). Struvite RSS decreased on diets inducing more acidic urine pH (p < 0.0001). Urinary calcium excretion and concentration increased with diets inducing lower urine pH (p < 0.0001), but oxalate excretion and concentration decreased (p < 0.001). CaOx RSS was not different between diets (p = 0.63). These results suggest that a lower diet base excess and resulting urine pH to support struvite dissolution do not increase the risk for CaOx crystallization in the range of urine pH representative of most commercial feline diets. Long-term studies are needed to confirm this.     

Phenothiazine toxicity

Thirteen adult cats were each fed consecutively five test diets: firstly a complete canned diet, and then four commercially available dry cat diets (New Formula Biscats, Cat Chow, Go-Cat and Whiskettes) for 7,13, 5, 4 and 4 weeks respectively. Urine samples were tested for pH and presence of struvite crystals. Body weight was recorded weekly.

Urine pH was ranked from acid to alkaline as follows: Whiskettes (pH 5.8), canned diet (pH 5.9), Biscats (pH 6.1), Cat Chow (pH 6.45) and Go-Cat (pH 6.5). The pH of urine when cats were fed Whiskettes, Biscats and canned diet was not significantly different. Biscats produced a urine pH significantly higher than Whiskettes but, in each case, these three diets produced a significantly lower urine pH than Cat Chow and Go-Cat. Struvite crystals occurred spontaneously in 9% of urine samples from cats when fed Whiskettes and Biscats, 71% when fed Cat Chow and 38% when fed Go-Cat: spontaneous struvite was not seen in any cat fed CX9. Haematuria was seen in 2.9% (2/69) urine samples from cats fed Cat Chow. One tom cat had a blocked urethra after 24 days on Go-Cat. No abnormalities were observed in any cat when fed canned diet, Biscats or Whiskettes.

It was concluded that of the four dry cat diets tested only Biscats and Whiskettes produce urine with an acceptably low rate of spontaneous struvite crystalluria.     

Effect of diet on struvite activity product in feline urine

Groups of male specific-pathogen-free cats were fed a basal, purified diet (A), with or without 0.45% added magnesium (MgCl2, diet B; MgO, diet C) or 1 of 2 commercial diets (D,E). Urine samples collected for 48 hours after 2 weeks of feeding were analyzed for calcium, magnesium, sodium, potassium, ammonium, sulfate, phosphate, oxalate, and citrate content. Concentrations were used to calculate the negative logarithm of the struvite activity product (pSAP), using a microcomputer-based program for calculation of supersaturation of the urine with crystal solutes. The pSAP value for all samples also was hand-calculated by use of an equation. Consumption of diet B caused a significant (P less than 0.05) increase in urine calcium concentration. Total urine phosphate concentration was lower in urine from cats fed diets A, B, or C than in urine from cats fed diets D or E. For the various diets, urine PO4(-3) was: 5.3 microM for diet A; 6.3 microM for diet C; 0.9 microM for diet E; 36 nM for diet D, and 0.5 nM for diet B. Consumption of diets B and C caused significant increases in urine magnesium concentration (53.1 nM and 49.1 mM, respectively). Ammonium ion concentration was highest in urine from cats fed diets B and D, 116.2 mM and 100.3 mM, respectively. When the pSAP, hand-calculated assuming ionic strength u = 0.2, was regressed on that calculated by use of the microcomputer program, the coefficient of determination was 0.96 (P less than or equal to 0.01).     

Evaluation of meat meal, chicken meal, and corn gluten meal as dietary sources of protein in dry cat food

The nutritional value of meat meal (MM), chicken meal (CM), and corn gluten meal (CGM) as dietary sources of protein in dry food formulated for adult cats was evaluated. Twelve healthy adult cats (11 males and 1 female) were used. Dry diets containing MM, CM, or CGM as the main protein source were given for a 3-week period in a 3 x 3 Latin-square design. Digestion and balance experiments were conducted during the last 7 d of each period. In addition, freshly voided urine was taken to determine urinary pH and number of struvite crystals. As compared with the CM diet, dry-matter digestibility was higher and lower for the MM and CGM groups, respectively. Percentages of nitrogen (N) absorption and N retention to N intake were higher in the MM group, and N utilization was not different between the CM group and the CGM group. All cats excreted alkaline urine (pH > 7). Urinary pH, struvite activity product, and number of struvite crystals in urine were lower for the CGM group. There was no difference in retention of calcium and magnesium among the groups. From the point of view of digestibility and N utilization, MM is superior to CGM, and CM is better than or equivalent to CGM as a protein source of dry foods for adult cats. However, when CM is used as a dietary protein source, some manipulation of dietary base excess may be needed to control urinary acid-base balance, because CM contains higher calcium and phosphorus.     

Urinary acidification in the prevention and treatment of feline struvite urolithiasis

Two groups of 12 cats were fed ad libitum an experimental dry expanded ration high in magnesium (0.37%, dry matter basis) and similar to most commercial dry cat foods in all other nutrients. The diet of one of the groups contained 1.5% ammonium chloride, which was added to the diet before processing. Urethral obstruction developed twice in 7 of the 12 cats fed the ration without ammonium chloride. Of the 5 remaining cats in that group, 2 had calculi in the urinary bladder and urethra at necropsy. In contrast, only 2 of the 12 cats fed the ration containing ammonium chloride had urethral blockage once; neither cat had another blockage. Both cats had been catheterized twice as paired controls before urethral obstruction. One of these 2 cats died from a urinary tract infection apparently introduced through the indwelling catheter, and at necropsy there were 2 small calculi in the urethra. At the end of the study, only 1 other cat fed the ammonium chloride diet had a calculus in the urinary bladder at necropsy; this cat had not had a urethral obstruction throughout the study. After each cat had 2 urethral blockages, its diet was changed. Four cats were fed the ration containing ammonium chloride and 3, a dry, commercial ration. Of the 4 cats fed the diet containing ammonium chloride, none developed another urethral obstruction within 6 months, and at necropsy, no calculi were in the urinary bladder or urethra. Two of the 3 cats fed the commercial ration experienced urethral blockage within 3 months. These 2 cats were then fed the diet containing ammonium chloride.(ABSTRACT TRUNCATED AT 250 WORDS)     

Urethral Obstruction in Male Cats: Transmission Studies

Urethral obstruction was produced by injecting centrifuged urine from cats with urethral obstruction into the urinary bladders of unaffected cats. Filtration of urine from affected cats did not remove the causative factor.     

ASSOCIATIONS BETWEEN ULTRASOUND AND CLINICAL FINDINGS IN 87 CATS WITH URETHRAL OBSTRUCTION

Urethral obstruction is a life‐threatening form of feline lower urinary tract disease. Ultrasonographic risk factors for reobstruction have not been previously reported. Purposes of this retrospective cross‐sectional study were to describe urinary tract ultrasound findings in cats following acute urethral obstruction and determine whether ultrasound findings were associated with reobstruction. Inclusion criteria were a physical examination and history consistent with urethral obstruction, an abdominal ultrasound including a full evaluation of the urinary system within 24 h of hospitalization, and no cystocentesis prior to ultrasound examination. Medical records for included cats were reviewed and presence of azotemia, hyperkalemia, positive urine culture, and duration of hospitalization were recorded. For medically treated cats with available outcome data, presence of reobstruction was also recorded. Ultrasound images were reviewed and urinary tract characteristics were recorded. A total of 87 cats met inclusion criteria. Common ultrasound findings for the bladder included echogenic urine sediment, bladder wall thickening, pericystic effusion, hyperechoic pericystic fat, and increased urinary echoes; and for the kidneys/ureters included pyelectasia, renomegaly, perirenal effusion, hyperechoic perirenal fat, and ureteral dilation. Six‐month postdischarge outcomes were available for 61 medically treated cats and 21 of these cats had reobstruction. No findings were associated with an increased risk of reobstruction. Ultrasonographic perirenal effusion was associated with severe hyperkalemia (P = 0.009, relative risk 5.75, 95% confidence interval [1.54–21.51]). Findings supported the use of ultrasound as an adjunct for treatment planning in cats presented with urethral obstruction but not as a method for predicting risk of reobstruction.