Antler Growth in Male and Female Reindeer Calves Occurs in the Absence of the Gonads

Abstract

Reindeer/caribou (Rangifer tarandus tarandus) differ from all other species of deer in their antler physiology in three notable ways: (1) antlers are developed in both sexes, (2) antlers begin to grow in young calves well in advance of puberty, and (3) antlers are cast and regrown annually in females, and both intact and castrated males. These observations suggest that, in contrast to the situation in other species, the initiation of antler growth in the young animal and the seasonal cycle of antler regeneration in the adult animal are temporal events not controlled by the secretion of gonadal hormones. To investigate the control of the initiation of antler growth, we monitored antler growth in two castrated male and two ovariectomized (OVX) female reindeer which had their gonads surgically removed at 5 to 15 days of age when there were no palpable antler pedicles (births 16 to 28 May). The animals were reared outdoors by their mothers in Tromso, Norway (70° N). All experimental animals initiated antler growth. The two castrated males and one of the OVX females developed normal spike antlers 2 to 36 cm long in the first year of life, while one of the OVX females developed only antler buds. In the animals that developed antlers, these were cleaned of velvet in the winter, cast in the spring, and new antler growth was initiated. There were small differences in the pattern of cleaning and casting compared with gonadally intact animals. These observations provide experimental evidence that the development, growth, and casting of the first antler can occur after postnatal gonadectomy. Nevertheless, gonadal hormones are thought to play an important role in dictating the timing of the antler cycle in reindeer as in other cervids, synchronizing the hard antler phase with other reproductive events.