Apparent Calcium Absorption in Growing Dogs of Two Different Sizes
The influence of the calcium (Ca) supply on the skeletal health of growing dogs and the ability of dogs to adjust the absorption of this element in cases of over- and undersupply has been investigated by various authors.
In most trials, Great Danes were used as the large-breed dogs (14), and Miniature Poodles, Beagles, or mongrels (57) were used as the small-breed dogs. Especially in the case of Ca excess, the Great Dane puppies developed clinical signs of skeletal disturbances, whereas the small-breed dogs showed no or only subclinical signs. However, not every large-breed puppy that consumes excess Ca develops skeletal abnormalities. That various breeds respond differently to dietary Ca excess is indicated by experimental results (8,9) as well as field studies (1012). The aim of this study was to investigate possible genetic influences on Ca balance during growth. These results suggest that there may be genetic differences in the regulation of Ca absorption in growing dogs: the FBIs absorb less Ca than the Beagles. Such a difference in Ca metabolism might be one reason for the differences in the sensitivity of different dog breeds to Ca excess. Schoenmakers et al. (14) showed that in Great Dane pups fed excessive Ca, the parathyroid hormone (PTH) setpoint remained low after the Ca supply was corrected. A mechanism like this might indirectly (because of reduced Vitamin D effect in the gut) or directly (via reduced Ca reabsorption in the kidneys) lead to lower Ca retention in these dogs compared with controls. Whether the effects of a 6-wk period of excessive Ca intake lead to a shift of the PTH setpoint in FBIs but not in Beagles is presently unknown.
Summarizing, it can be hypothesized that a breed-dependent difference in Ca metabolism may exist. Indirectly, this might lead to different responses to Ca excess. This may explain the inconsistent reports from the literature regarding developmental skeletal problems caused by Ca malnutrition.