When I see something like that, the first thought that comes to mind is disease, sickness etc. hence I am not sure if I would shoot it. I shoot for fun, sport, thrill yes but also for FOOD. If I knew an animal I was to eat was sick in some way that might just possibly affect me or those eating the meat as well, I would skip that animal.
In this case, it is likely simply a genetic variant but why? What were the previous years sheds like on this animal? What are the causes of this? Are there environmental factors affecting this deer leading to this abnormal growth? Could some form of contamination have caused this? Excessive minerals in the diet... what source... heavy minerals, open pit mining, contaminated drinking water etc? These and many other chemicals are accumulated in animal tissues and travel up the food chain hence, older animals have more toxicity as well as those higher on a food chain.... This is also a greater problem in males who by nature have no ability to reduce their natural body fat (where most chemicals are stored) like lactating females do. Not so sure I would want to eat this guy without some testing of the meat for palatability first.
A remarkable creature none the less. I wonder what the does thought of him?
T