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Nutrient Metabolism

Intestinal Calcium Absorption in Growing Dogs Is Influenced by Calcium Intake and Age but Not by Growth Rate¹

M. A. Tryfonidou^2*, J. van den Broek, W. E. van den Brom^* and H.A.W. Hazewinkel^*

^* Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, 3584 CM Utrecht, The Netherlands; and Centrum for Biostatistics, Utrecht University, 3584 CC Utrecht, The Netherlands

²To whom correspondence should be addressed. E-mail: M.A.Tryfonidou{at}vet.uu.nl.

The effects of calcium (Ca) intake (V_I), age and growth rate on intestinal Ca absorption were studied in growing dogs. Two breeds of dogs differing in their growth rate (67 Great Danes and 23 Miniature Poodles) were raised on diets differing only in their Ca content (range 0.33 to 3.3 g/100 g diet on a dry matter basis). Repetitive Ca balance studies were performed with the aid of ⁴⁵Ca from 6 wk (i.e., after weaning) until 6 mo of age. Several models were investigated expressing true Ca absorption (V_a) as a function of V_I, breed and age. V_a was directly proportional to a function close to V_I^0.82 being a continuation of the high Ca needs for mineralization of the growing skeleton. This curvilinear relationship between V_a and V_I and the inverse relationship between fractional Ca absorption and V_I indicated the presence of active and passive Ca absorption in weaned growing dogs. A model in which these two components of Ca absorption can be discerned revealed that active Ca absorption underwent age-dependent changes, whereas passive absorption remained constant and accounted for 53% absorption of the V_I. At low V_I, active absorption contributed to a significant part of the V_a, whereas at excessive V_I active absorption was negligible and passive absorption was the driving force for causing supra positive Ca balance. Intestinal Ca handling did not differ between breeds with dramatically different mature body size and growth rates.

KEY WORDS: • True Ca absorption • ⁴⁵Ca balance studies • age-dependent changes • Ca intake, dogs

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