In SW MN/E SD -- dock is fairly common. I have one grazing paddock that frequently floods out and the first thing to regrow is curly dock. Cattle tend to ignore it in my experience. In hay, I'd say the same thing, cattle pick around it.
One site said cattle would need to eat 10-20 lbs of green leaves to get sick.
I've been around cattle and curly dock my entire life and I can't think of an instance that an animal got sick and it was linked to that plant.
Plant net app. Is what I have. I'm not big app person. That one is handy, and it's free. I actually want to run up in people yards sometimes and see what their shrubs, flowers, ect. Are but figure I better now. Although, I have if they were close to the road. I enjoy landscaping and like doing what certain things are if I don't know.