I have been trying for several days to get my horse to go into the nether. I am playing survival vanilla Minecraft 1.14.4. At first, I thought maybe it wasn't possible to get a horse into the nether. But I did some research and found that as long as you are not riding the horse, it will go through the portal. This is a quote from the Official Minecraft Wiki on Horses:
It is impossible for a player to use a Nether portal while on a horse. It is possible however, to enter the portal on the horse and then dismount, sending the horse through the portal on its own, or use a lead to position the horse, then push it through the portal.
I tried both pushing the horse through the portal and dismounting from the horse in the portal multiple times but nothing seemed to work. I restarted the game and my computer and it still wouldn't work.
**I am able to go through the portal.
Here are some pictures of me dismounting from my horse while positioned in the portal:
I am curious if anyone else is experiencing this issue. Please let me know of any tips to get my horse into the nether.