Auswirkungen des Natrium- und Rohproteingehalts sowie der Proteinqualität im Futter auf die Harnzusammensetzung von gesunden Katzen

Effects of variations in sodium and crude protein concentrations as well as protein quality in a diet on urine composition of healthy cats This study aimed at investigating the effects of variations in sodium and crude protein concentrations as well as protein quality in a diet on urine composition of cats. In particular, risk factors for the formation of calcium oxalate urine stones were evaluated. For this, seven experimental diets were fed to 8 healthy adult cats. Diets varied in concentrations of sodium (0.38 %, 0.65 %, 1.14 % and 1.43 % in dry matter), crude protein (34.7 %, 43.8 % and 57.4 % in dry matter) and collagen-rich greaves meal (12 % and 35 % in the diet). Each diet was fed for a three-week adaptation period and a subsequent one-week collection period. For the collection periods, cats were housed individually in metabolic cages to collect their urine and faeces. Feed and water intake were recorded daily during the collection periods. Concentrations of urinary anions and cations, relative supersaturation of the urine with calcium oxalate and struvite as well as faecal dry matter, crude nutrient and mineral concentrations were determined. The key findings of this study are briefly listed below. Increasing levels of dietary sodium were associated with an enhanced urine volume and renal sodium excretion. The concentration of calcium in the urine of the cats was not affected, but the urinary excretion of calcium increased from 0.62 to 1.05 mg/kg body weight/day with increasing dietary sodium levels. Urinary oxalate, citrate, phosphorus and potassium concentrations decreased at higher sodium intakes. The pH of the urine ranged between 6.33 and 6.45 among the treatment groups (P > 0.05). The relative supersaturation of the urine with calcium oxalate was not affected by varying sodium levels in the experimental diets. Consequently, in the context of the formation of calcium oxalate urine stones, this part of the study shows some positive effects of a high sodium intake in cats over a short time. The concentrations of calcium in the urine as well as the relative supersaturation of the urine with calcium oxalate remained unaffected and the concentrations of oxalate in the urine were reduced. This finding could especially contribute to prevent the formation of calcium oxalate urine stones. With increasing concentrations of crude protein in the diet, an enhanced urine volume could be observed as well as an increase in urinary calcium concentrations, renal calcium and oxalate excretion and relative supersaturation of the urine with calcium oxalate. The pH of the urine ranged from 6.34 to 6.66 among all groups, while no unidirectional influence of the dietary protein level could be detected (P > 0.05). With the exception of the enhanced urine volume, these effects of a high protein diet might be critical with regard to the prevention of calcium oxalate urine stones in cats. When feeding the diet with a higher percentage of collagen-rich greaves meal, less urinary excretion of calcium could be detected. The reason for this effect remains unclear and should be investigated in future studies. To be able to give reliable feeding recommendations for the prevention of calcium oxalate urine stones, the results of the present study should be verified through further investigations in cats that are either predisposed or diseased.