I think a lot of things that are supposed to be poisonous really aren't unless large amounts are eaten, like if they are most of the diet. Mine love poke, and oak leaves, acorns, (I just make sure they don't get too much of those, they will OD if they can for sure) they eat pine like crazy while pregnant (which some say is bad), mine eat fescue in our fields without a problem (but I don't feed hay with fescue in it towards the end of pregnancy). I've even seen them eating mintweed which scared the crud out of me. But darn, it is literally everywhere here, there is just no way to get rid of it. I've seen my horses munch on it as well. I guess a little is ok, and hopefully as long as they have plenty other to eat?
Hope yours are ok!