Abstract
Dietary Mg restriction is generally considered to contribute to the prevention of struvite urolithiasis in cats, but its effects on faecal and urinary excretion of Ca and P have not been systematically investigated. The present study seeks to fill the gap. In a 4 x 4-week crossover study, ovariectomized cats were fed on purified diets containing either 0.40, 0.79, 1.59 or 3.17 mmol Mg/MJ (0.19, 0.38, 0.76 and 1.52 g Mg/kg diet). Increasing the dietary Mg level from 0.40 to 3.17 mmol Mg/MJ by the addition of extra MgCO3 raised urinary and faecal excretion of Mg from 0.14 to 0.68 mmol/MJ and from 0.28 to 1.66 mmol/MJ respectively. The 8-fold increase in Mg intake significantly raised urinary excretion of Ca from 0.06 to 0.09 mmol/MJ. Apparent absorption and urinary excretion of P were depressed by 13 and 25% respectively when the dietary Mg level was raised from 0.40 to 3.17 mmol/MJ. A dietary level of 0.40 mmol Mg/MJ (0.19 g Mg/kg diet) was found to be sufficient to maintain Mg balance in the adult ovariectomized cats fed on the purified diet.