Reclaiming pasturland with pigs/pig tractor & toxic plant question

We recently purchased some acreage of which approximately 1.5 - 2 acres is old overgrown pasture now covered in dogbane. We were thinking that we could make a decent sized pig tractor and allow weaner pigs to till the soil for us and make that section useable again. However, I have read that dogbane is toxic to cattle, horses, etc. Can anyone tell us if this will work with pigs? We don't want to use pesticides but I'm concerned about the toxicity of the dogbane.

If we hack down the weeds, will the roots that the pigs have access to still be toxic or is it just the plant?

Any knowledge/experience would be helpful.

I find that our pigs don't eat the toxic things, rather they trample those plants down. Toxic things tend to taste bad. Think of it as a form of inter species communications. We used to have a lot of dogsbane but I rarely see it now. The pigs done a wonderful job of helping to renovate what were abandoned pastures, some of which had grown up to forest. We recut low to the ground and back to the old stone walls to reopen the pastures. We've done this twice to gradually expand our fields. See:

http://sugarmtnfarm.com/2009/08/02/field-clearing-grapple-skidder/

We use managed rotational grazing techniques:

http://www.google.com/search?q=site:sugarmtnfarm.com%20rotational%20grazing&ie=utf-8&oe=utf-8

Rather than making a pig tractor I would suggest using step in posts and polywire. Poultry netting with some modification works too:

http://sugarmtnfarm.com/2008/06/12/poultry-netting-for-pigs/

http://www.google.com/search?q=site:sugarmtnfarm.com+fencing

We have about 400 pigs out on our pastures and buy no commercial feeds or grains. While we have chickens, ducks, geese and often sheep it is the pigs who bring home the bacon for our farm.

Thank you for your useful information. We've pastured pigs about 10 years ago and used electric fencing along the perimeter. Although we don't want to breed pigs anymore we prefer pasture-raised.

I will be looking through your links tomorrow, when I come in to break from the heat...

Thanks again.