Bone metabolism during antler growth in female reindeer

Two female reindeer (Rangifer tarandus) were investigated for alterations in skeletal metabolism during the annual antler growth cycle. During July and January, rib samples were obtained by biopsy after double tetracycline labeling for gravimetric, chemical, and histomorphometric analyses. Though antler length increased from 8 to 55 cm between April and September, body weight increased from only 56 to 77 kg. Rib bone density (g/cm3) increased from 1.39 +/- 0.01 (mean +/- SEM) in July to 1.53 +/- 0.01 in January, and Ca content (mg/cm3) increased from 213 +/- 8 to 300 +/- 14, respectively. Histomorphometric data indicated that rib bones were more porous and active in July and had a higher turnover rate than did January samples. Plasma 1,25(OH)2D, parathyroid hormone (PTH), and osteocalcin levels were significantly lower and estradiol levels were significantly higher in the January as opposed to the July samples. The data indicate that during antler growth, female reindeer undergo bone loss that corresponds to the changes in plasma calcemic hormones and estradiol levels. This bone loss is eventually repaired when antler growth stops.