Plasma 25-hydroxyvitamin D in growing kittens is related to dietary intake of cholecalciferol

Vitamin D synthesis by growing kittens exposed to ultraviolet light is ineffective. Concentration of 25-hydroxyvitamin D (25-OHD) in plasma (the most useful index of vitamin D status) was measured in six groups each of seven kittens given a purified diet (12 g calcium and 8 g phosphorus/kg, calculated metabolizable energy = 20 kJ/g) that contained either 0.0, 3.125, 6.25, 12.5, 18.75 or 25 microg of cholecalciferol/kg diet. All kittens received these diets from 9 to 22 wk of age, and the two groups given the 0.0 and 3.125 microg cholecalciferol/kg treatments continued to receive the diets until they were 34 wk old. Total and ionizable calcium and phosphorus in plasma were not affected by treatments. No adverse clinical changes were observed or found on radiographic examination of the kittens at 22 or 34 wk of age. Plasma concentration of 25-OHD was linearly related (r2 = 0.99, P < 0.001) to dietary intake of cholecalciferol. Plasma concentration of 25-OHD in kittens given the diet without added vitamin D was significantly less at 22 wk than at 9 wk, whereas kittens receiving the diet containing 3.125 microg cholecalciferol/kg had significantly higher 25-OHD concentrations at 22 and 34 wk than at 9 wk of age. Kittens given the 6.25 microg cholecalciferol/kg diet had plasma 25-OHD concentrations at 22 wk > 50 nmol/L which is considered replete for humans. An allowance of 6. 25 microg (250 IU) of cholecalciferol/kg diet is suggested to provide a margin of safety.