Yes, reindeer do lose their antlers once a year. The process of antler shedding is called "antler casting." Reindeer shed their antlers in the summer months, usually in June or July. As the antlers grow, they become covered in a thin layer of skin called the "velvet." During the summer, the velvet is shed, and the antlers become hard and mature. The process of antler shedding is a natural part of a reindeer's life cycle, and it occurs every year.