We get plenty of horses on our trails. The ones who know that they were built by, maintained by, and constantly used by riders are generally really good (other than often walking horses up jumps and making a mess of them).
The ones who stumble across the trails and think that they personally discovered and own them are less friendly when bikes whizz around blind corners at speed.
If I see horses, I give a wide berth, or stop and let them pass quietly. Lots of our long established trails nearby are being closed to bike to allow better access to horses and walkers....the last thing I want to do is ruffle more feathers on my home trails.