Delay Losing Antlers

One of our older breeder bucks scores a little over 200". He lost his first half of his antlers on January 19. He still has his other side. He has about 2" of growth on the side he lost and the side that still has antlers is swelling around the base. Last year he went about 1 month after losing his first side. Not sure what causes this. It's typical for him.