Antlers are an amazing feat of nature.  Aside from providing protection for Elk, Moose and Deer, there have been studies that indicate that moose antlers may also assist in amplifying their hearing. *
Antlers grow very quickly and are naturally shed each year and re-grown again.  The new antlers can grow up to an inch every day, and initially are covered by a velvet texture that the animal rubs off on trees and brush.   This "velvet" antler is full of nutrients and has been prized for centuries for it's reputed health benefits for people.  Antlers are bone that is fed by blood carried in the outer velvet covering.
Deer, Elk, and Moose need both protein and minerals to grow their antlers. This is in contrast to horned animals whose horns are made of keratin (like fingernails), who do not shed, and who need only protein to grow their horns.  Animals who have horns, like cattle, sheep and goats add gradually to their existing horns rather than shedding yearly. 

Our chews are made from the naturally shed calcified antlers that remain after the velvet has been rubbed off.