The majority of the horses used were owned by professional horse trainers who supplied them for the film's production. These trainers have a large network of horses suitable for filming, and they carefully select which animals are best suited for each specific role.
Some horses may have also been owned by individuals who participated in the film's production, but this information is not publicly available.
It's important to note that the film's producers likely hired the horses and their trainers on a temporary basis for the duration of filming. Once the movie was complete, the horses likely returned to the care of their original owners.