Intestinal calcium absorption in growing dogs is influenced by calcium intake and age but not by growth rate

Abstract

The effects of calcium (Ca) intake (VI), 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 (Va) as a function of VI, breed and age. Va was directly proportional to a function close to VI0.82 being a continuation of the high Ca needs for mineralization of the growing skeleton. This curvilinear relationship between Va and VI and the inverse relationship between fractional Ca absorption and VI 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 VI. At low VI, active absorption contributed to a significant part of the Va, whereas at excessive VI 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.