From my Wild Mammals of New England book:
New antlers begin to grow in April. Growth is slow at first but becomes much faster as summer advances. By August or September full development is reached when the velvet dries and is rubbed off on shrubs and trees. The antlers are usually shed in December or January, but may be shed as late as March.This was newly shed because there was still a bit of blood at the base. Pretty cool, eh, wot?!