Dietary protein levels affect water intake and urinary excretion of magnesium and phosphorus in laboratory cats.

The effects of dietary protein levels on food and water intake, and urinary excretion of magnesium (Mg) and phosphorus (P) were examined in cats fed dry-type diets. Four adult female cats were used for trials in a 4 x 4 Latin square design, and fed diets with increasing protein content (25.9, 38.3, 51.4 or 65.2% in dry matter) daily from 9:00 to 13:00. While daily food intake was almost constant regardless of the dietary protein level, water intake and urine volume increased with increasing the dietary protein. Daily urinary excretion of P increased in response to the increase in dietary protein level. The urinary concentration of P was positively related to nitrogen (N)-intake. In contrast, daily urinary excretion of Mg was not affected by the dietary protein level, and the urinary concentration of Mg was negatively related to N intake. A dry-type diet with a high protein content might be effective in preventing the deposition of Mg salts in the urinary tract of cats under the meal-fed condition without affecting food intake because of both the lower concentration of urinary Mg resulting from the increase in urine volume and, probably, urinary acidification.