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Calcium Metabolism in Great Dane Dogs Fed Diets with Various Calcium and Phosphorus Levels¹

Herman A. W. Hazewinkel^*,2, Walter E. Van Den Brom^*, Arie Th. Van 'T Klooster, George Voorhout and Ank Van Wees^*

^* Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, University of Utrecht, The Netherlands Department of Husbandry and Nutrition, Faculty of Veterinary Medicine, University of Utrecht, The Netherlands Department of Veterinary Radiology, Faculty of Veterinary Medicine, University of Utrecht, The Netherlands

The influence of dietary calcium on calcium metabolism was investigated in growing dogs that reach an adult body weight similar to that of humans. Seven groups of dogs (n 5) were raised on a diet with a composition meeting the National Research Council (NRC) requirements (1974), but differing in calcium content, with or without a constant ratio to phosphorus. Control dogs fed 1.1% calcium and 0.9% phosphorus (all on a dry matter basis) were fed ad libitum (n = 10) or in restricted amounts (n = 6); dogs fed high calcium (3.3%) diets received either 0.9% phosphorus (n = 6) or 3.0% phosphorus (n = 6); dogs fed low calcium (0.55%) diets received either 0.9% phosphorus (n = 5 + 6) or 0.5% phosphorus (n = 8). Food intake, circulating total calcium and inorganic phosphorus concentrations and calcium metabolism, with ⁴⁵Ca kinetics, were studied at 8, 14, 20 and 26 wk of age. Except for the difference in food intake in two groups at 14 wk (i.e., 0.55% calcium-0.9% phosphorus higher and 3.3% calcium-0.9% phosphorus lower, respectively, than the controls) no differences were noticed during the rest of the study. The mean plasma calcium concentrations did not differ between groups during the studies, whereas that of inorganic phosphorus revealed temporal aberrations in two groups. An absorption coefficient of 45–66% was found for the control group. High and low calcium diets gave rise to values of 23–43% and 70–97%, respectively, for irrespective of the phosphorus content of the diet. The amount of calcium absorbed was nevertheless considerably higher in the dogs fed the high calcium diet than in the control dogs. The dogs fed the high calcium diets had also a higher calcium retention than found in the low calcium group, which was not different from the control group. The conclusions were young dogs fed a diet with a calcium content of 3.3% (with either 0.9 or 3.0% phosphorus) have a significantly elevated absorption and retention of calcium and seem unable to protect themselves against chronic excessive calcium intake, and young dogs of this large breed elevate the absorption of calcium to >90% of the ingested amount when raised on a diet with 0.55% calcium (with either 0.5 or 0.9% phosphorus), resulting in a calcium absorption and retention not differing from that in control dogs, the latter despite the occurrance of severe osteoporosis.

KEY WORDS: • symposium • dogs • dietary calcium • dietary phosphate • skeletal mineraltization • ⁴⁵Ca kinetics

¹ Presented as part of the Waltham International Symposium on Nutrition of Small Companion Animals, at University of California, Davis, CA 95616, on September 4–8, 1990. Guest editors for the symposium were James G. Morris, D'Ann C. Finley and Quinton R. Rogers.

² To whom correspondence should be addressed: Department of Clinical Sciences of Companion Animals, University Utrecht, P.O. Box 80.154, 3508 TD Utrecht, The Netherlands.