How smart are pigs and how quickly can they be trained?

I'm writing a book, and in one scene I need a sorcerer to practice a memory spell on an animal. Preferably an animal you'd find on a farm. I was thinking to have him use a shock collar or rod (like what you use to train dogs) to train this animal to be scared of something, then perform the memory spell to see if the animal forgets its fear. I've heard pigs are quite smart. Would a pig work or should I just stick with a dog? Any other suggestions for animals would work too. I've thought about using a horse as well.