Antlers are bony extensions of the skull that grow from attachment points called pedicles. The antler grows from the tip in late winter and spring. The antler starts out as cartilage which is replaced by bone. While the antler is growing it is covered in vascular skin, called velvet, which provides nutrition to the developing antler. Velvet makes the antler look fuzzy. Once the antler reaches its full size, the velvet dries up and falls off the antler. Without a blood supply the antler dries. Eventually the bone at the pedicle is destroyed by osteoclasts (a type of bone cell that breaks down bone tissue) causing the antler to fall off.
Antler size varies with age, increasing for several years until reaching a maximum size. Only males in most cervid species have antlers, the exception being reindeer (caribou) females who also have antlers. However, occasionally other cervid females with high testosterone levels will grow antlers.
Antlers are shed and regrown each year, regulated by the length of day in temperate and Arctic regions.
Growing antlers requires enormous nutritional expenditure. So why do deer and other cervids grow antlers? Antlers are used to attract females. Large antlers indicate their bearer has great metabolic and food gathering ability. Females choose stags with the largest antlers because large antlers indicate strength and fertility. Also, antlers are used when competing with other males for dominance.
Antlers that have fallen off, called “sheds”, are gnawed on by small animals as a source of calcium and other minerals. Traditionally sheds have been used, ground or as extracts, in Asia as dietary supplements and for a variety of medicinal purposes. Recently Western cultures have begun to also utilize cervid antlers. Extracts of velvet, harvested from growing antlers, are now popular among athletes because these extracts are believed to build and repair muscle tissue. (There is no scientific evidence for this claim.) I do not want to imagine how the velvet is harvested.
This mule deer (Odocoileus hemionus) in velvet was photographed along the Blue Sky Road in Hart Mountain National Antelope Refuge (Oregon).