Yes, for a portion of the treatment of PTSD.
There are three phases I use to treat trauma. The first phase is the stabilization phase.
I believe that working with horses could be very useful for that phase; you bring a person to an arousal level that's lowered and you build their coping skills. You make sure that they are doing well in everyday life before going into the traumatic event, because you could really destabilize them a lot if you would just go into it when they're already pretty shaky. In that first phase, using the horses would be really useful.
There's the third phase of reintegration, once the trauma has been processed, once we have looked into the thoughts that keep a person feeling guilty, feeling shameful, feeling responsible, or feeling not good enough. Then we can start doing work with horses again and bring in their families or their children or their spouse and get their supports back up.