Hiya I believe when a horse passes over it is lovingly back in it's true spiritual form surrounded by other spirit horses and horse loving angels (when i pass over i will happily bring horses back to the spirit world and care for them) your horse will be in a very happy place indeed - never worry about that.

Also don't be surprised if you get a visit, horses do that! you might find hoof prints on the morning dewy grass when there is no horse to be seen or get a clear cut vision, it's like a goodbye,,, be open to it, horses always say goodbye to their master.