Bone-remodeling rates of the Beagle: a comparison between different sites on the same rib

The standardized colony-raised male Beagle is being used more frequently for research purposes. The rib of this dog is an ideal bone on which to measure haversian bone-remodeling activity. To date there has been little indication as to whether there has existed any natural statistically significant differences in bone-remodeling rates along the length of the rib of this dog. To answer this question, standard samples were procured from the proximal, mid-shaft, and distal portions of the 5th, 7th, 9th, and 11th ribs after tetracycline labeling. It was found that there exist in the normal state statistically significant differences between the 3 portions on all the ribs examined, as refers to ratio of cortical to total bone area, number of osteoid seams, number of resorption spaces, activation frequency, and bone-formation rate. These differences are significant at the 0.001 level and may give rise to a wrong interpretation by the unwary investigator. The results of this investigation stress the importance of standardizing the biopsy site on the rib that is to be examined.