OK, so they're property...but the property was not shown to have been damaged, or otherwise rendered unfit for slaughter. Therefore, no mischief.

If someone poisoned the pigs, or damaged them in some material fashion, then the charge might stick. 

But the only evidence in this case was that the defendant gave the pigs water, which did not preclude their entry into the food chain.

If you think that should be otherwise, write your MP or MPP and seek to change the laws accordingly. But don't bring obviously losing cases at great public expense, when the Courts are already clogged and real criminals are walking free due to delay in prosecution.