Effects of antler growth on annual changes in skeletal bones of red deer (Cervus elaphus) stags

Abstract

To determine the characteristics and extent of changes in rib and ilium bones during the annual antler cycle, a group of 6 red deer (Cervus elaphus) stags was studied from May 1995 until March 1996. From a description of growth and mineralisation of antlers in red deer (Muir et al., 1985) the greatest effects of antlerogenesis on skeletal bone metabolism were expected to occur during the calculated period of calcium deficiency (90-120 days post-casting).

Porosity and mineral density of rib, ilium and antler bone biopsies, collected 6 times throughout the trial, were determined by back-scattered electron imaging (BSE imaging) and ashing. Serum hydroxyproline concentration was determined by spectrophotometric assay from blood samples collected fortnightly over the duration of the trial and used as a biochemical marker of bone resorption.

No changes in mineral density of bone material were recorded for rib or ilium samples at any stage of the antler cycle. Mid-shaft antler mineral density increased (p<0.01) between 60 and 170 days after antler casting. In terms of bone content, rib samples tended to be most porous at 60 and 123 days after antler casting. Ribs were least porous (p<0.05) at 170 days after casting (following the full antler hardening). No change in porosity of ilium samples was detected during the trial.

Mean serum hydroxyproline concentration was elevated (p<0.05) from 17.5 ± 0.9 µmol/l to 29.6 ± 0.9 µmol/l during the period of most rapid antler formation (60 - 140 days after antler casting) and returned to the baseline concentration following full hardening of antlers.

Increased porosity of rib cortex and elevated serum hydroxyproline concentration indicate occurrence of net resorption and increased bone turnover, at least in rib cortex, during antler growth. Bone mass of affected bones was recovered immediately following, or during final antler hardening. The results of this trial reinforce previous findings in white-tailed (Odocoileus virginianus) bucks and mule deer (Odocoileus hemionus) which indicate that cortical bone of the skeleton is lost during antler growth with no effects on cancellous bone. It is noteworthy that periods of elevated skeletal bone turnover were initiated several weeks before calcium deficiency due to antler formation was expected to occur.