Hi Denny. I deal with this all the time. You don't have to chop and drop the whole blackberry thicket all at once. Do it a little at a time. The hogs will be curious and will follow you around. Chop and drop above a particular root mass that you want them to attack, and dump a bucket of their feed around and over it. They will get the hang of it and will make short work of all those blackberries soon enough if you repeat this procedure, root mass by root mass.
I am getting ready to put 16 head on a blackberry-infested pasture next week, and I expect to be out there doing this in rainy-ass Washington every day.

Ultimately, those uprooted blackberries dry out. The canes can then become biochar or hugelkultur feedstock. But the root balls go right into the biochar barrel. I'm taking no chances with them, haha.