Be cautious about allowing stock access to cut, wilted plants. Often what they won't touch, alive/growing, becomes attractive when wilted. Your county ag extension should have resources to ID plants.
Another deterrent to poisoning is ensure mineral mix available so animal doesn't have unusual drive to seek missing item. I also try to ensure everyone has enough to eat as a hungry animal wiil be prone to eat whatever to not feel hungry.
I id’d it w some photos. I’m confident that’s what it is. Growing just outside my dead pen ironically. Sprayed it. Sheep won’t be in that pasture due to spear grass which should be done in a week. Spear grass hasn’t bothered the flock in the past but gets all over the dogs. This is the first hemlock I’ve seen. I wonder if it came from a neighboring abandoned farm. Thanks for the advice.