(Top) Representative confocal microscopy images demonstrating the presence of fluorochrome labels in the endocortical and intra-cortical compartments of both virgin/normal Ca and lactation/low Ca groups. The virgin/normal Ca controls lacked fluorochrome labels in the periosteal compartment. Oxytetracycline (labeled ‘T’ in the images) was given on day 2, calcein (‘C’) was given on day 14, xylenol orange (‘X’) was given on day 21, and alizarin (‘A’) was given on day 26 of the recovery phase. (Bottom) Degree of mineralization (mineral-to-matrix ratio) plotted as a function of tissue-age and compartment. Data are presented as the means and standard deviations. There was not a significant difference between groups in the intra-cortical compartment. Endocortically, the two-way ANOVA indicated a significant tissue-age effect (p=0.031) and a significant interaction term (p=0.013), with no significant group effect (p=0.602).