We have cougars here and I have yet to have one attack any livestock. As someone posted above unless it is starving a full grown horse and cow are much too large for a cougar to take down.
I would not worry about it you running on a trail are more vulnerable to attack than your horse is grazing in a pasture.
We do have donkeys but only to protect from feral dogs. We have yet to ever lose a cow or calf to a coyote. Too many mice and cotton tails around for them to be interested in something as hard to kill as a calf or a colt. Shalom