Poisonous to Horses

I am so glad we are boarding Blondie at a stable right now, so that we can research the plants on the property (and get the fencing in place).

I am finding plants that can hurt horses, and we need to remove them.  Here are some of the poisonous plants that we found here (I have milkweed growing along the creek and isn't near where the horse will go, or the goats):

and Dogbane (no photo yet).  I guess we have some work to do.

Amaranthus (pigweed family)?

I'm working with a park expert and a master gardener, to identify flowers and weeds on my property.  However, we are still unsure of this red colored one.  I think the chickens are the reason we have it all over this year.  I'm not exactly sure what it is.  Unless I hear back from the experts, I may have to keep looking in books and on-line.