Effects of testosterone on pedicle formation and its transformation to antler in castrated male, freemartin and normal female red deer (Cervus elaphus).
Pedicles and antlers are male deer secondary sexual characters. As such, development of these structures is under the control of androgen hormones. Pedicle growth is caused by increasing and elevated plasma testosterone (T) levels, whereas first antler transformation from a fully formed pedicle occurs when the T levels are decreasing. Castration prior to pedicle initiation abrogates future pedicle and antler formation. Female deer also have the potential to develop pedicles and antlers, but they do not normally express this phenotype due to lack of sufficient androgen stimulation. Previous studies have shown that female white-tailed deer could be readily induced to grow pedicles as well as antlers by singular administration of exogenous androgens (EA), but in red deer (Cervus elaphus) singular or irregular EA treatment could only stimulate castrated male, normal or ovariectomised females to grow pedicles, but not antlers. The present study was set out to test whether these EA-induced pedicles in red deer failed to give rise to antlers was because they were constitutively incapable of doing so, or because the plasma T profile naturally exhibited in intact stags was not achieved by the androgen treatment used in these previous studies. Eight castrated red deer stag calves, 3 freemartins (females which were born co-twin to males), and 3 normal female red deer were used in the present study and treated with EA, either as biweekly injections for the castrates or as implants for freemartin and females until the late stage of pedicle growth. Blood sampling was carried out biweekly for the analyses of plasma T and IGF1 concentration. The results showed that the natural plasma T profile in the experimental deer was successfully mimicked through regular EA treatment and subsequent withdrawal at late pedicle growth stage. All castrated males, 2 out of 3 freemartin, and 1 out of 3 normal female red deer formed not only pedicles, but also antlers. Based on these results, we conclude that EA-induced pedicles at least in red deer of the genus Cervus, like those in the genus Odocoileus, are constitutively capable of giving rise to antlers, if they are of sufficient height.
Li
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AgResearch Invermay Agricultural Centre, Private Bag 50034, Mosgiel, New Zealand. chunyi.li@agresearch.co.nz
Littlejohn
R P
RP
Corson
I D
ID
Suttie
J M
JM
D000818:Animals; D000999:Antlers / Q000187:drug effects / Q000254:growth & development*; D001835:Body Weight / Q000187:drug effects; D002417:Cattle; D003670:Deer / Q000502:physiology*; D004343:Drug Implants; D005260:Female; D005611:Freemartinism / Q000503:physiopathology*; D007273:Injections, Intramuscular; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D008297:Male; D009919:Orchiectomy; D011863:Radioimmunoassay; D012886:Skull / Q000187:drug effects / Q000254:growth & development; D013739:Testosterone / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*
D004343:Drug Implants; D013739:Testosterone; D007334:Insulin-Like Growth Factor I