Being a person who puts my pigs out all the time...i quite honestly
don't worry about what plants are around (other than chemicals but
since it's my own backyard not an issue).
I find that all the pigs I've ever owned won't eat what's bad for them.
If there is grass around, or dandelions, that is what they focus on.
If I put them in my garden...watch out carrot leaves! But the
potatoes, cabbagem onions etc.. they ignore.
On the lawn, they go nuts for grass, dandelions, bind weed BUT ignore
the creeping charlie which is, unfortunately, everywhere.
I"ve never seen them go for something that might not be good for them.
They do have a good survival instinct for the most part.