How long does it take a horse to eat a round bale?

There is no one answer to that question. It's dependant on too many things, such as the season and weather temperature, the size and eating habits of your horse, as well as how much other grazing or food he or she is getting and if they have unlimited, 24-hour access to the round bale, (which is not recommended) Generally, (and this can vary quite drastically) one round bale of hay will last an average sized horse 5 - 6 weeks. Two horses - about a month or so, Three horses - about 2 1/2 to 3 weeks, etc. *This is assuming that the round bale does not get ruined by rain and the horses urinating and defacating on it, etc.