Bone Fractures Due to Low Calcium Diets

Several years ago 1 we reported the observation that a diet, adequate with respect to vitamin D and phosphorus but deficient in calcium, will produce a skeletal structure which is hard but light and fragile, in young growing animals. The thin-walled bones, showing no evidence of rickets, do not bend easily, have a nearly normal bone ash, and are not enlarged at the ends. Spontaneous fractures are common and are located at the point of greatest stress which varies with different species. In calves and dogs the fractures usually occur in the femur. In rabbits we find the vertebrae are the common site of fracture. Boelter and Greenberg 2 recently reported that rats on a low calcium diet frequently have spontaneous fractures of the long bones. According to our interpretation of their observations the vertebrae of rats are also susceptible to fracture.

During our study of this problem we carried out an experiment, using 5 litters of rabbits. Four of the litters were divided at weaning (3-5 weeks of age) each into 2 groups. Half of each litter was placed on a basal diet composed of whole oats 60%, alfalfa 18%, molasses 2%, whole wheat 10%, cracked yellow corn 8.5%, NaCl 0.5%, Na₂HPO₄ 1%, plus irradiated yeast to supply 6.5 U.S.P. units of vitamin D per gram of ration. The other half of each litter received this basal diet plus 1% CaCO₃. The basal ration contained 0.199% Ca and 0.513% P. The fifth litter was treated in the same manner, except that these animals were 8 weeks old when they were removed from their mother's pen where they had access to a commercial rabbit feed. This interval on a normal feed evidently carried the young past a critical period, since the animals of this litter placed on the basal ration remained healthy and their growth was equal to that of their litter mates fed the basal ration plus 1% CaCO₃.