Are horses afraid of pigs?

It's a common understanding that horses are terrified of pigs.

Horses that aren't used to pigs will often shy away from them - perhaps because pigs are omnivores that wouldn't shy away from a meal of horse meat.

Pigs also smell funny even to humans and make strange noises. Oh, and they're inclined to come running up to say hi, which horses also don't appreciate.

However, I've also known an entire of herd horses to welcome a pet pig as a buddy...so once they get used to them they're fine. Or perhaps once they realize that pig is being well fed by the humans...