Whitetail bucks begin growing antlers in March but they do not reach substantial size until late May or early June. Antlers are covered with a soft velvet coating, which contains a network of blood vessels to nourish the underlying bony structure.
By August, the antlers are fully grown and the velvet dries, cracks, and eventually comes off in strips. The animals usually hasten the process by aggressively rubbing trees and shrubs. In Pennsylvania many bucks lose the velvet in late August or early September.
The bucks above were photographed in Shenandoah National Park on August 28th. Usually the larger bucks lose the velvet first, but in this instance the opposite is true.
This small Pennsylvania buck which I am able to observe on a regular basis still had velvet on September 14th, but on the morning of the 16th it was mostly gone. As you can see it is quite a bloody affair when the velvet first comes off.