Abstract
The physiological control mechanisms underlying the histogenesis of the pedicle, which precedes antler growth, from the frontal bones of male deer are poorly understood. The aim of this study was to investigate the extent of pedicle/antler regeneration after removal (for histological evaluation) of the antlerogenic region or pedicle tissue during pedicle development to determine whether the subsequent pattern of regeneration could contribute to the understanding of pedicle histogenesis and the mechanism of the transition between permanent pedicles and deciduous antlers. The contralateral pedicles of six stags were not removed and these data serve as controls. All deer were observed frequently and measurements of regeneration were made in March after all antler growth had ceased for that season. The developmental stage of the pedicle was determined by a combination of pedicle height measurements and histological studies. The results showed that pedicle formation histologically covers three stages: a period of intramembranous ossification (when the pedicle is less than 5 mm in height), a period when the ossification pattern changes (when the pedicle is between 5 and 28 mm in height) and a period of modified endochondral ossification (when the pedicle is over 30 mm in height). In all ossification stages some deer regenerated neither antlers nor pedicles. The pedicles which regenerated following the loss of antlerogenic tissue at the intramembranous ossification stage were shorter than the controls (P < 0.01), but longer than the pedicles regenerated after pedicle removal at the transitional stage in the pattern of ossification (P < 0.01). No pedicle tissue was regenerated if the pedicles were removed at the endochondral ossification stage and antlers were directly formed from the deer's head. Thus the final height of the regenerated pedicles was closely linked with the histological ossification stage of the original pedicle at removal. Antler regeneration took place at all stages but two deer grew pedicles only when tissue removal took place during the transition period. Overall the results provide evidence that the potential to regenerate a pedicle diminishes as the pedicle increases in height and the necessity for pedicle growth to precede antler growth also decreases. The fact that some deer, whose tissues were removed at the transition period of ossification change, regenerated pedicles but failed to generate antlers highlights the importance of this stage for the transition between the permanent pedicle and the deciduous antler. The results provide evidence for an hypothesis that it is the transition between ossification types which signals the end of pedicle development and the onset of antler development. Β© WileyβLiss, Inc.