We have a lot of milk weed, both in pastures and our crop fields. Dogbane hasnt been too bad, but the last couple years we have been seeing more and more around, espeacially in our crop fields. All I can say is if you can try and get it under control. Both dogbane and milk weed are kinda tough to control, but 24d and banvel do pretty good jobs of getting it if applied at the right stage of growth, mainly when its younger.
Normally animals wont eat it, but the problem comes when forage is baled or chopped. Then, the cattle/horses eat it. Some toxic plants become less toxic if fermented or dried, but not these. Fifteen to 30 grams of green leaves has been reported as causing death of a horse or a cow. Nasty stuff for sure!
Jenna