aggressive behavior all of a sudden!

Question
I have 2 neutered pot bellied pigs,(brothers) about 100 lbs each. They are about 3 years old. We own a petting zoo and I have raised them together since they were a couple months old. One of the pigs has started non-stop attaching the other. I have never even seen them squabble before. They do have worn down tusks that I saw when the farrier was trimming their feet. Could this be causing problems? How do I figure out if the pig is in discomfort or sick? What else could cause this very docile pig to react this way to his brother?
I am quite disturbed as this is a childrens petting zoo and I cannot have this type of behavior.
Thank you for your time

Answer
Pigs see the world as ladder, and each pig (and person) has his own rung on the ladder. Pigs also reach emotional or mental maturity between ages 2 and 4.

One possibility is that the attack pig was, up until recently, the #2 pig, and his brother was the #1 or dominate or Alpha pig. Now that he's older, he wants to be the Alpha pig. So he is attacking the other pig because he is insecure about his position, he wants to establish his dominance. If this is the case, then chances are things will settle down soon, when both pigs have established the new pecking order and settled in. Once they've established who is boss and who is not, you can encourage them to remain peaceful by going along with their decision. In other words, when filling food bowls, fill the Alpha pigs bowl first.

Pigs are very good at hiding pain or sickness. That's because in the wild, a sick or injured pig is an easy dinner for a hungry predator. Sometimes, when one pig in a group is sick or injured the other pigs may try to push that pig out. But, that's really not a common behavior in pot-bellied pigs.

What is more common is that the sick or injured pig was a dominant pig. The lower pigs sense the sick pigs weakness. To a lower pig, this is a chance to steal the dominant pigs position, so they attack the sick pig. It isn't so much about chasing the sick pig away, it's more about establishing dominance over the sick pig.

At age 3 their tusks should be just starting to come out to the lip. Pigs like to grind their teeth to keep their tusks worn down. Also, fighting and rooting can break a tusk off.

Try separating the pigs at meal time and check each pig out closely and carefully. Look for any sign of injury, or illness like runny eyes or nose.

It sounds as if the farrier was there recently, did the behavior begin after his visit? If so, then something about his visit triggered this behavior. If the pig being attacked was the dominant pig but now has sore feet, that is the kind of situation where the other pig would try to become dominant through aggression. If this is the case, there will probably be fighting until the pigs are comfortable with their new positions, or the injured pig recovers and reclaims his role as dominant pig.

I highly recommend Priscilla Valentines book Pot-Bellied Pig Behavior and Training. Pris really understands how pigs think and explains their point of view. She has several chapters devoted to aggression in pigs, and goes into much more detail than I can here. Her book is available from Amazon.com or her website www.valentinesperformingpigs.com