Sometimes incorrectly referred to as horns, deer antlers are cast and regrown annually. Horns, on the other hand, grow continually much like hooves. Another difference between horns and antlers is that horns, like hooves, are composed of keratin, whereas antlers are composed of bone. The actual composition of antlers depends upon their stage of growth. Growing antlers are 80 percent protein and 20 percent ash.
Antlers are most dense on young deer and tend to become more porous as the animals grow older.
Antler growth requires a substantial amount of protein and minerals, yet body growth always takes precedence. This is true especially for young deer because they are still putting energy into body growth. Measuring specific nutritional and mineral effects on wild deer antler growth is difficult because of the animals' large home range and varied diet. A number of studies on penned deer have found relationships between nutrition and antler growth in young deer. Whitetail fawns fed a ration containing less than 9.5 percent protein developed smaller racks, weighed less and cast their antlers earlier than fawns fed 16 percent protein rations.