Lots of factors affect antler shedding, including weather, length of day, nutrition, etc. But testosterone levels probably have the greatest effect. A buck living near a large population of does that keep coming into estrous will maintain high testosterone levels, often well into March or April. However, a large population of does can also lead to over browsed habitat, which leads to poor nutrition... which can then cause earlier antler dropping.
Now, if you see bucks with fully developed antlers in May or June, that would be really unusual.
