Urinary composition of cats is affected by the source of dietary protein.

Feline lower urinary tract disease is an important clinical problem in cats. Epidemiological data based on urinary stones submitted for examination show over the last decade a consistent trend for struvite calculi to decrease and calcium oxalate to increase (1,2). The risk for cats to develop urolithiasis is related to dietary and nondietary factors. Higher solute concentrations, a subsequent supersaturation of the urine, and the lower frequency of urination can favor the formation of crystals and calculi. Although urinary calcium excretion is normally low in cats and not strongly related to dietary mineral intake, the excretion of phosphorus, magnesium, sodium, and potassium was repeatedly demonstrated to be strongly diet dependent (3). The dietary mineral composition influences the postprandial pH significantly and can therefore predispose cats and dogs to develop crystaluria or urolithiasis (4,5). Oxalate is important due to its potential to form crystals with calcium. Urinary oxalate excretion is resultant from dietary oxalate and the metabolism of ascorbic acid, glycine, tryptophane, phenylalanine, and hydroxyproline (6). Experimentally, a vitamin B-6 deficiency was found to increase the daily urinary oxalate excretion from 1.5 to 24 mg BW 1 (7). Similar observations were made in young cats, fed either a vitamin B-6–deficient diet or a diet supplemented with 8 mg/kg vitamin B-6 (8,9). Dietary protein intake could be an important factor determining the urinary composition in cats, but has not been intensively studied. Urine is the most important excretory medium for metabolites from protein metabolism. Urine volume shows a positive correlation with dietary protein intake (3). Urea, creatinine, and ammonia are the main metabolites that are excreted. Even in healthy cats a certain level of protein excretion is considered as normal. In this study the influence of dietary protein quality and quantity was investigated with regards to the urine composition and the excretion of oxalate and crystaluria in cats.