Remember this weed from last week? I took your suggestions and contacted our local extension agency, and this is what I heard back:
I believe this plant is Cutleaf Nightshade Solanum trifolum. As D---- mentioned, this plant is poisonous to livestock. I suggest scouting the pasture and eradicating all of the plants you can find. Digging and removing the entire plant will work if there are a small number in the pasture. Widespread populations may require the use of herbicides. Since it sounds like you have found only 2 plants, that is a good sign. It is an annual weed and it may come back from seed in the future. Keep an eye on the field and remove any plants before the fruit develops and deposits the seed to prevent future weeds from growing.
As a horticulturalist, I am not knowledgeable enough to give advice on livestock. I would echo Diana's suggestion of contacting your vet. They would know best about your horse's health.
So, my horses didn't eat it, they spit it out. I think it must be unpalatable to them.
Thanks to everyone who commented on Beautiful's baby book pictures. I'm a proud mama who only publishes the good shots! The bad ones--and there are many--go in the cyber garbage can.
Is she roaned? Good question! I can't figure her color out! I don't think so. It appears to just be very light. I think her color is very unusual.
For more information on the "Wild Tomato" weed that grew in my pasture: here's a link.