The structure of pedicle and hard antler bone in the European roe deer (Capreolus capreolus): a light microscope and backscattered electron imaging study

Abstract

Deer antlers are deciduous bony structures that develop from permanent frontal outgrowths, the pedicles. While growth and bone architecture of antlers have been studied in greater detail, information on pedicle formation and structure is scarce. The present study provides information on the structure of pedicle and hard antler bone in the European roe deer. A pronounced seasonal variation in pedicle architecture was observed, with high porosity around antler casting and a very compact bone structure during the hard antler stage. These observations suggest a corresponding marked variation also in the biomechanical properties of the pedicles. The seasonally alternating extensive resorption and formation processes make the pedicles of older deer heavily remodeled structures. Pedicles increase in thickness by apposition of primary bone that subsequently becomes replaced by secondary osteons. The antler cortex of roe deer is largely composed of a tubular framework of woven bone trabeculae with some remnants of mineralized cartilage, and primary osteons that have filled in the intertrabecular spaces. Secondary osteons are scarce, denoting little remodeling in antlers, which can be related to their short lifespan. The occurrence of cement lines around primary osteons indicates resorption on the trabecular scaffold prior to infilling of the intertrabecular spaces. The outer cortex showed a higher autofluorescence and a more immature structure than the main cortex, suggesting that it was secondarily formed by periosteal activity. Pedicles and antlers constitute a functional entity, and future histological and/or biomechanical studies should therefore consider both components of the cranial appendages.

Smaller does not mean worse: variation of roe deer antlers from two distant populations in their mechanical and structural properties and mineral profile

“…What about the mineral profile of the antler? Making comparisons for the antler’s mineral profile with other deer species is not a simple procedure, but certain metabolic processes in the growth of antlers could be similar (Kierdorf et al , ). Moreover, in roe bucks, like other Cervids, the minerals necessary for the formation of the antlers come also from a mobilization of mineral components from skeletal bone material (Baxter, Andrews & Barrell, ; Fandos & Burón, ), and a reversible cyclic osteopenia occurs in internal bone during the antler cycle (Brockstedt‐Rasmussen et al , ).…”

“…One of the main reasons for studying antlers is their rapid growth and annual regeneration which make them a good model for studying bone tissue and the possible factors in the bone growth process (Kierdorf et al , ; Landete‐Castillejos et al , ). Generally, these factors, apart from the genetic characteristics, are populational density (Santiago‐Moreno et al , ), climate (Mysterud et al , ; Landete‐Castillejos et al , ) and the food quality (Brown, ).…”

Revisiting the links between bone remodelling and osteocytes: insights from across phyla

“…The obvious question (as also for the small rodents) is why do these animals suffer the metabolic cost of maintaining these osteocytes? Indeed, antlers are re‐grown each year during an extraordinarily rapid burst of growth, when a trabecular bone and cartilage scaffold is constructed and then infilled with osteonal bone to form the solid antler; by contrast, the antler's bony pedicle (base) is part of the skull and persists from year to year (Kierdorf, Kierdorf & Boyde, ; Krauss et al , ; Kierdorf et al , ). During the growth period, antlers are fragile and their bearers are very careful not to load them heavily (e.g.…”

“…If little remodelling occurs during the growth phase of these massive bones and if the osteocytes are mostly dead at the time of peak loading events, when remodelling would be most useful, why do antlers need osteocytes in the first place? Again the question of ‘lifespan’ (this time of the antler, not the whole animal) may be important here: the antler bone is only at its final state (at maximum size, full of osteocytes, and alive), for a week or so and remodelling may not have sufficient time to occur (Kierdorf et al , , ). The few secondary osteons appearing in late‐stage antler growth (as opposed to the many secondary osteons in the non‐deciduous pedicles of antlers) support this argument (Kierdorf et al , ), as does the continued osteoblastic/osteoclastic activity in the antlers of castrated fallow deer, which are not shed (Kierdorf et al , ).…”

“…Again the question of ‘lifespan’ (this time of the antler, not the whole animal) may be important here: the antler bone is only at its final state (at maximum size, full of osteocytes, and alive), for a week or so and remodelling may not have sufficient time to occur (Kierdorf et al , , ). The few secondary osteons appearing in late‐stage antler growth (as opposed to the many secondary osteons in the non‐deciduous pedicles of antlers) support this argument (Kierdorf et al , ), as does the continued osteoblastic/osteoclastic activity in the antlers of castrated fallow deer, which are not shed (Kierdorf et al , ). However, the debate about whether antlers are living or dead and the many atypical features of osteons in antler and/or pedicle – cement lines surrounding both primary and secondary osteons, secondary osteons apparently forming as primary bone is still being deposited, large secondary osteons possessing multiple vascular canals (Gomez et al , ; Kierdorf et al , ) – suggest that the modelling and limited remodelling processes in this system may be more complicated than we appreciate.…”