Why?

It's generally because the mods didn't like something about it.

Ok, thank you.

It may be that it's been removed temporarily for editing OR whilst they deal with a complaint about it.  Either it'll come back or you'll get a message explaining what happened.

In the meantime perhaps you could have a read of the Terms of Service which might give you a clue.  http://www.champdogs.co.uk/html/terms.html

It could also be because a poster has two posts running at the same time about the same topic.

It did go off topic, could that be the reason, if so I guess those post that were off topic will be removed and the thread returned, I would have expected that you would have been told why if it has been permanently deleted. If it is because it went off topic I think I may have been one of the guilty ones and I apologise.