Abstract
This study aimed to investigate the impact of dietary calcium (Ca) and phosphorus (P), derived from bone meal, on the feline urine composition and the urinary pH, allowing a risk assessment for the formation of calcium oxalate (CaOx) uroliths in cats. Eight healthy adult cats received 3 canned diets, containing 12.2 (A), 18.5 (B) and 27.0 g Ca/kg dry matter (C) and 16.1 (A), 17.6 (B) and 21.1 g P/kg dry matter (C). Each diet was fed over 17 days. After a 7 dayś adaptation period, urine and faeces were collected over 2×4 days (with a two-day rest between), and blood samples were taken. Urinary and faecal minerals, urinary oxalate (Ox), the urinary pH and the concentrations of serum Ca, phosphate and parathyroid hormone (PTH) were analyzed. Moreover, the urine was microscopically examined for CaOx uroliths. The results demonstrated that increasing levels of dietary Ca led to decreased serum PTH and Ca and increased faecal Ca and P concentrations, but did not affect the urinary Ca or Ox concentrations or the urinary fasting pH. The urinary postprandial pH slightly increased when the diet C was compared to the diet B. No CaOx crystals were detected in the urine of the cats. In conclusion, urinary Ca excretion in cats seems to be widely independent of the dietary Ca levels when Ca is added as bone meal to a typical canned diet, implicating that raw materials with higher contents of bones are of subordinate importance as risk factors for the formation of urinary CaOx crystals.
Highlights
The role of dietary calcium (Ca) and phosphorus (P) in the formation of feline uroliths is subject of controversy
High dietary P levels lead to an increased intestinal absorption of P and enhanced renal P excretion, which is considered as another predisposing factor for the formation of magnesium ammonium phosphate (MAP) [1]
High urinary Ca concentrations can contribute to the formation of Ca phosphate uroliths [7], they are by far less common compared to Ca oxalate (CaOx) or MAP [8]
Summary
The role of dietary calcium (Ca) and phosphorus (P) in the formation of feline uroliths is subject of controversy. It has been suggested that restricting dietary Ca would reduce the renal Ca excretion and lower the risk for Ca oxalate (CaOx) uroliths in cats [1]. Beside its relevance for the formation of CaOx uroliths, dietary Ca may be a potential risk factor for the development of magnesium ammonium phosphate (MAP) urolithiasis in cats, mainly depending on its effects on the acid base metabolism [5] and on blood Ca concentrations. The reduced levels of PTH may inhibit the renal tubular reabsorption of magnesium (Mg) and enhance the urinary supersaturation with Mg, ammonium and phosphate [6], increasing the risk of MAP formation. High dietary P levels lead to an increased intestinal absorption of P and enhanced renal P excretion, which is considered as another predisposing factor for the formation of MAP [1]. High urinary Ca concentrations can contribute to the formation of Ca phosphate uroliths [7], they are by far less common compared to CaOx or MAP [8]
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