Determinants of bone mass, density and growth in growing dogs with normal and osteopenic bones.

Survey radiographs of all the growing dogs aged up to 6 months, which were presented to the IVRI polyclinics during the 10 year period were screened to study the determinants of bone mass, density and growth. On the basis of clinical history and radiographic evaluation of long bones, the cases were categorizes as normal or osteopenic. The relative cortical density (RCD), cortical index (CI), diameter of bone at the distal metaphysis (DDFM) and the width of the growth plate (WFGP) were determined by taking the femur as a model bone in German shepherd, Doberman and Spitz breeds of dogs at different age groups. The results showed that RCD was the least in 0-2 month old normal growing dogs in all the breeds. As the age advanced up to 6 months the RCD increased 20-25% and at 6 months, Spitz and Doberman showed significant increase (P<0.05) in the RCD. In osteopenic bones, RCD remained less (25-50%) than that of normal animals at all age groups, and at 2-6 months of age, RCD in osteopenic bones was significantly lesser than in normal animals in GSD and Spitz breeds. The CI was also the least at 0-2 months of age in normal dogs. The CI increased about 50% at 4-6 months of age in GSD and Spitz. Whereas in Dob., there was no appreciable change in the CI at different age groups, and at 2-6 months it was significantly (P<0.05) lesser than that of Spitz. In osteopenic bones, the CI was 25-75% lesser than that of normal animals at different age groups, and at 4-6 months there was significant difference (P<0.05) between the normal and osteopenic bones in GSD and Spitz. The DDFM was the least in 0-2 month old normal growing dogs, and as the age advanced, it increased 10-20% up to 6 months. However, no significant difference in the DDFM was seen between breeds and also between the normal and osteopenic bones at different age groups. In normal animals, the WFGP was the highest in the early age, subsequently it reduced 50-75% and at the 4-6 months there was a significant decrease (P<0.05) in all breeds of dogs. And at the 4-6 months, there was significant (P<0.05) difference in the WFGP between breeds, it was the least in Spitz and maximum in Dob., suggesting faster growth plate closure in Spitz than in GSD and Dob. breeds. In osteopenic bones, WFGP was generally more than in normal animals, and at 4-6 months (about 3-5 times more) there was significant difference (p<0.05) between the normal and osteopenic bones in all breeds, indicating that physeal closure may be delayed in osteopenic bones. The results indicate that among different breeds Doberman breed has the least bone mass and may be more prone to osteopenia; whereas Spitz has the strongest bone.