Histological structure of antlers in castrated male fallow deer (Dama dama)

Abstract

Antlers are periodically replaced cranial appendages that, except for the reindeer, are grown only by male deer. The annual antler cycle is controlled by seasonal fluctuations of sex steroid concentrations in the blood, and accordingly castration of male deer causes deviations from normal antler growth. The present study investigated antler histology of castrated fallow bucks (Dama dama). Castration in early spring was followed by casting of the hard antlers carried by the bucks and the growth of a new set of antlers, which remained in velvet permanently. In the following year, numerous bony protuberances developed from the original antler surface. Further growth of these protuberances, which were formed by subperiosteal intramembranous ossification, led to a marked increase in antler diameter in the affected areas. Compared to antlers of intact bucks, the antlers of the castrates showed histological signs of immaturity, suggestive of a reduced bone remodeling and an impairment of the mineralization process. These changes point to the dependence of the above processes on a stimulation by higher levels of sex steroids. Two years after castration, the antlers also developed integumental thickening and showed an initial formation of skin outgrowths. Cystic structures were present in the skin, which were often filled with a presumably sebaceous and/or keratinous material. Formation of intradermal bone or cartilage was not observed in the antlers of the castrated fallow bucks. The histological structure of the skin outgrowths suggested that they were caused by a hypertrophy of the dermal component of the velvet. Due to the localized bone overgrowth, resulting from the periosteal bone apposition onto the original antler surface, skin-lined infoldings originated, which reached deep into the newly formed bone. Our study revealed no indication of invasive/destructive bone growth in the antlers, i.e., of a penetration of the newly formed bone tissue into the pre-existing bone. The hypertrophic bone growth in the antlers of the castrates is compared with other forms of periosteally derived hypertrophic bone formation, including osteomas, in the mammalian skeleton. It is discussed whether the skin and bone outgrowths of the antlers of castrated fallow bucks may be classified as benign tumors. Key words: antler; fallow deer (Dama dama); castration; bone; skin; histology Antlers are periodically cast and regenerated cranial appendages that develop on top of permanent processes (pedicles) of the frontal bones of deer. Except for the reindeer (Rangifer tarandus), in which both sexes carry antlers, these are normally grown only by male deer (Goss, 1983;Lincoln, 1992). Since the antler physiology of reindeer differs markedly from that in other deer species, this special case is not considered further and only the typical situation in male deer will be presented.The annual antler cycle is controlled by seasonal fluctuations in the blood levels of sex steroids

Healed antler fracture from a giant deer (Megaloceros giganteus) from the Pleistocene in Poland

“…These observations suggest a healing process of approximately 2-3 months, since antler tissue regeneration progresses more rapidly than other bone tissue regeneration (Kierdorf et al, 2004;Li, 2012). Consequently, the death of the animal appears to have occurred during antler healing, or may have occurred following velvet shedding from the healed antler, but prior to antler shedding.…”

“…Histological evaluation of antler structure, development, and pathology has been focused on extant cervids, including sika deer (Cervus nippon) (Gao et al, 2010) and fallow deer (Dama dama) (Kierdorf et al, 2004). Similar information on antler histology of extinct cervids is scanty (Paral et al, 2007).…”

Deer Antlers – A Model of Mammalian Appendage Regeneration: An Extensive Review

“…Mature antlers consist of a central portion of cancellous bone and an outer layer (cortex) of compact bone, with a narrow transition zone between the two portions [66] . Formation of a dense antler cortex is apparently androgen-dependent as is indicated by its lack in castrates [69] .…”

“…The bony protuberances present in antlers of castrates are formed by appositional growth from the periosteum ( fig. 7 ) [69] . Both the skin and bone overgrowths of fallow deer can be classified as benign tumors, and malignant transformation of these structures has not been observed [69,80] .…”

“…These studies suggested that the abnormal skin outgrowths, which were termed antleromas [8] , represent a hypertrophy of the dermis [69,80] . The bony protuberances present in antlers of castrates are formed by appositional growth from the periosteum ( fig.…”