Last winter there was a horse killed by what was suspected to be a cougar, only 30 miles from my farm and my horses. This happened in south central WI. A second horse in that herd was wounded but lived. This happened in rural Watertown, WI.
I hope you’re not leaving your horses outside after dark anymore. Wouldn’t cross my mind to leave mine out at night, due to concerns about theft as well as cats, vandals, perverts, and some psycho who is going around our town cutting off horses’ tails (the hair, not the actual tail bone, so it’s ugly but not painful).