A well-fed horse should live for 5 days. I've tested this with a new horse. I've lost over a dozen horses since the wipe. I have a stable and keep them fed. Seems I can't keep one for more than 12 hours, regardless. My neighbor said he has had the same problem, and was disappointed because he outfitted his horse with armor and horse shoes.
I am playing on US Survival
-Chinaski
Server: Pure