Don't laugh at my story because there is nothing funny about it.
I started running into feral pigs on my trail rides in the mountains and canyons south of the ranch about 5 years ago. They were terrified of them. One caused a serious wreck with a good really trail gelding that I was riding. It ended up with me getting a $9000.00 helicopter ride, a 3 week hospital stay and nearly a year in re-hab and PT. This was the ONLY serious wreck I had riding in more than 50 years of training horses, So --- I take pigs really seriously.
I bought a pot bellied pig and have had her in a pen near the barn for over 4 years. She has been perfectly happy by herself for the last 4 years. There is a big tree next to her pen and there is a horse tied to it right now. I have several horses that still do not like her, but now they all tolerate her. I ride them back and forth and back and forth until they walk by without trying to bolt away from her.
If I have a horse that has been ridden very hard and is tired, that is where I will unsaddle him and tie him up until he is cooled out and ready to be put up. It is one of these horses that is standing next to her pen right now. I know of no other way to get a horse to tolerate a pig. They just do not like them or trust them unless they have been raised around them. Then, they are fine with them.