Outside of a direct and immediate threat to your family, I would say there is never a reason to take the law into your own hands, that being said, this comment in some way may explain his over the top reaction:
Elias described “a terrifying previous incident” about six weeks beforehand when trespassers had threatened Williams with a shotgun and made threats about burning his property. That led to him “reacting on the spur of the moment to a situation he believed was far more serious than it actually was”.
A pre-sentencing report compiled to assist the judge spoke of Williams suffering “unresolved trauma which impaired his judgement” as a result of the earlier incident. Elias emphasised that the trainer had shown insight and changed his behaviour, calling the police to deal with a subsequent incident rather than intervening himself”
Oddly if the incident itself had happened 13 days later, changes to the law meant that the judge could have suspened the whole sentence, that being said, it would appear that he will most likely be out no later than 18 months into his sentence, with the balance of the three years to be served in the community.
It could end up being an extremely costly lesson not just in the immediate future but also long term in potential damage to his reputation which could affect his ability to bring in new owners to his yard (or even keep his current ones).