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Department of Molecular Biosciences, School of Veterinary Medicine, University of California, Davis, CA 95616 and * Waltham Centre for Pet Nutrition, Waltham-on-the-Wolds, Melton Mowbray, LE14 4RT, UK
1To whom correspondence should be addressed.
We previously demonstrated that a purified diet containing 3.125 µg of cholecalciferol/kg was adequate to maintain plasma concentrations of 25-hydroxyvitamin D in growing kittens. With the use of this concentration of cholecalciferol, the response of growing kittens to varying levels of calcium in purified diets was measured. Five groups (treatments 15), each comprised of seven weaned kittens, were given diets containing 3.8, 5.0, 6.0, 7.2 or 8.1 g calcium/kg diet (Ca:P ratio of 1:1.25) from 9 to 18 wk of age. Two further groups of kittens (treatments 6 and 7) received similar diets containing 6.0 g Ca/kg diet, with Ca:P ratios of 1:1.55 and 1:2.61, respectively. No clinical signs of calcium deficiency were observed, i.e., growth rate, energy intake and plasma total calcium were not affected by the treatments. However, ionized calcium was significantly lower in kittens in treatment 7. Plasma phosphorus was lower in kittens in treatment 7 than in kittens in treatments 1, 2, 3 and 4, and there was a negative relationship between dietary and plasma phosphorus concentrations. Kittens in treatment 7 had a significantly higher alkaline phosphatase concentration in plasma than kittens in treatments 1, 2, 3 and 5. Kittens in treatment 1 had a lower percentage of bone minerals measured by dual-energy X-ray absorptiometry than kittens in treatments 26. These results indicate that the calcium requirement of growing kittens is not >6.0 g/kg diet, (calculated metabolizable energy ~20 kJ/g) and that kittens are not very sensitive to inverse Ca:P ratios up to 1:1.55.
KEY WORDS: calcium phosphorus cats osteocalcin parathyroid hormone