horses suffocate when going into nether portal

Horses susffocate when goign into small (normal sized) nether portals. 

when they enter the nether they end up in the obsidian and die. 
or in a netherbrick wall . 

horses mules  and donkeys all ahve this problem 
they can also not be ridden into a portal ( at least for sure with pigs) and have to be pushed.