Sadly as you have found, boar trios generally don’t work out long term. It’s incredibly difficult to get the character compatibility right and most boar trios fail.
While some chasing is normal in a bond, due to the issues boar trios face this can very quickly turn into full on fights. Sadly such a fight warrants immediate and permanent separation and if that were to occur, depending on who was fighting, it’s possible they could all end refusing to live together and you’ve then got three single piggies. Best case scenario is two of them dont fight with each other and can remain together post fight and then one will be single.
They are now right at the thick of the hormones and this is when problems start to come to light. As you are noticing one seems unhappy, now is sadly the time to split them up before things take a more serious turn, and the one unhappy piggy becomes further withdrawn. If you have two of them who do get on well, then keep them together and separate one of them into his own cage side by side with the pair.
The cage sizes you have - is that a 3 foot by 2 foot cage? If so, then then the cage isnt big enough to use at all. The welfare minimum for two sows is 4ft by 2ft but that isnt big enough for boars. The minimum size for two boars is 5x2ft with 6ft x 2ft being the recommended size.
The size increases greatly when attempting a boar trio from 12 sq ft recommended size for two boars to 32 square feet minimum when attempting a boar trio. However, even with the large space, a boar trio is still not likely to make it but giving them as much space as possible allows them to get away from each other and can diffuse tensions a little.
The pair who remain together will need a 6ft by 2ft (180x60cm) cage to themselves. Your 4x4 ft run is a good size for two boars to have as a run space.
The piggy who ends up single will need to be kept side by side with the pair so they can interact through the bars only so stop him from becoming lonely. He will need a minimum of a 4ft by 2ft cage while he is single but ideally he will then be bonded with his own character compatible friend, again in a separate cage measuring 6ft by 2ft cage.
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