In 18w08b, zombie horses are invisible and only their shadows are visible (as you can see from the attached image. Despite, the zombie horse texture does exist in its folder, so I suppose it is a bug.
MC-126299
Zombie horses are invisible
Resolved
Duplicate
0
Noam
(Unassigned)
Unconfirmed
Minecraft 18w08b
Retrieved
Duplicate of MC-124147