Reindeer shed their antlers once a year, usually during the summer months. The antlers are made of bone, and they grow during the spring and summer when reindeer have access to plenty of nutritious food. In the fall, the antlers begin to harden, and by the winter, they are fully mature. During the winter, reindeer use their antlers for combat and to attract mates. In the spring, the antlers fall off and a new set begins to grow in their place.