Working with animals can be tricky. Cats won't do anything you tell them and dogs well you have to feed them all the time. That's where horses come in. They are like giant two thousand pound dogs that eat grass and poop everywhere. Here's my short and dirty guide to working with horses:
Stunt Doubles and Horse Masters
You're going to need them because most actors can't ride horses and for shorts you won't want the liability. If you can find an actor that also is a capable rider you're going to need a horse master to take care of the horses when you're not riding them. Keep them happy so you're actors or stunt doubles don't get bucked off them.
Make sure they are not overworked, horses don't work well on sets when they have to be ridden around for 12-16 hours. Which is why blocking out exactly what you need them for and when you need them will not only reduce your shot list to a few key shots but they will also prevent them from getting agitated and hurting someone.
This can also be resolved by have doubles for horses, but if you're on a low budget film like we were, we just transported the horses from a local ranch to our location and took the back after the first day.
Transporting horses can be tricky, you don't want to stress them out prior to transport many horses have been familiarized with transport from a young age and most will readily allow themselves to be loaded into a transport vehicle. A small minority of horses can be difficult to transport and you'll want either avoid using them or not use horses at all. Thinking logically can help, if you put a sick horse on a truck it's going to be worse off when it gets off. After all it is a two thousand pound animal in a confined space for however many hours or minutes you plan on putting them in a trailer; what do you expect.