The consequences of living longer—Effects of an experimentally extended velvet antler phase on the histomorphology of antler bone in fallow deer (Dama dama)

Abstract

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Distribution, structure, and mineralization of calcified cartilage remnants in hard antlers

“…The present study demonstrated the regular presence of calcified cartilage remnants in the distal portions of hard antlers from all three studied species, thereby confirming the results of previous studies ( Landete-Castillejos et al, 2012 ; Kierdorf et al, 2013 , Kierdorf et al, 2021 ). In the late-formed, distal antler regions, resorption of the framework of calcified cartilage was thus typically incomplete, while further proximally the cartilage was largely or entirely replaced by bone in the course of antler histogenesis.…”

“…The persistence of calcified cartilage in the distal antler regions and the lack of any significant remodeling of the antler bone are regarded as the inevitable consequence of the short (only few months) lifespan of antlers ( Kierdorf et al, 2021 ). The latter view is supported by the observation (in fallow deer) that when the lifespan of antlers is experimentally extended by antiandrogen treatment, the calcified cartilage in the antler tips is completely replaced by bone in the course of marked remodeling ( Kierdorf et al, 2021 ). Further evidence of this process was the frequent presence of secondary osteons and resorption cavities in the antler bone of the experimental animals.…”

“…The persistence of calcified cartilage in antlers reflects their short lifespan of only a few months that does not allow for complete resorption of calcified cartilage and its replacement by bone in the youngest antler regions. The short-lived nature of antlers is also the reason for the absence of any significant remodeling of antler bone ( Kierdorf et al, 2021 ). Our analysis confirmed that the calcified cartilage in antlers is more highly mineralized than the bone matrix.…”

“…Also Skedros et al (2014) did not observe calcified cartilage in the studied regions of the hard antlers of mule deer, which however did not include the antler tips. In contrast, other authors have reported the persistence of remnants of calcified cartilage in hard antlers (especially their distal portions) of red deer ( Landete-Castillejos et al, 2012 ), European roe deer ( Capreolus capreolus ) ( Kierdorf et al, 2013 ), and fallow deer ( Kierdorf et al, 2021 ).…”

“…While the pedicles are permanently skin-covered, the unique type of skin (velvet) that invests the growing antlers is shed after completion of growth, thereby exposing the bare bony (‘hard’ or ‘polished’) antlers. These are dead structures that are carried for a few more months, until they are detached (antler casting) and replaced by a new set of antlers ( Goss, 1983 ; Currey et al, 2009 ; Gomez et al, 2013 ; Landete-Castillejos et al, 2019 ; Kierdorf et al, 2021 ). The timing of the antler cycle is under strict control of circulating androgens ( Lincoln, 1992 ).…”