I'm not a veterinarian, but it looks like his ears have some signs of past frostbite (dark blotches and irregular edges). I wouldn't think that Belgium would be that cold, so maybe this species is especially sensitive, or this individual came to the zoo from a more northern zoo, or perhaps it's an older individual with poorer circulation? Sorry for the wild speculation, but it caught my eye in this very good photograph.
@Summer Tanager If I'm reading ZTL correctly this is either a male that came from Howletts (UK) or a male born at Pairi Daiza. There were some - for Belgium - freezing cold days in the winter before this image was taken, but not something that could not be handled with a shelter or stable. I don't know about the age of this animal, other than that if it's the UK male it has been at Pairi Daiza since 2018. I can't comment on the veterinary aspects of deer.
@KevinB Thank you for the background - you did a deep dive into this and I appreciate that. I've only seen six or seven Hog Deer here in the U.S. and of them were at southern zoos, so it may be a more cold-sensitive species than I thought or this is a more normal condition of aging than I think. Thank you again!
