Hi evie
I dont really have any knowledge of horses but about a year ago i was asked by a friend if i thought Reiki could help a his girlfriends horse, it was suffering with a leg problem and hadn't been ridden for 3 weeks.I agreed to give reiki a try and really just applied reiki to the areas of the back where i thought the chakras would be (based on the human body)concentrating quite heavily on the tail bone area and also working locally on the swollen area low down on the leg, as i was working a small group of stable girls gathered and couldnt believe how quiet and calm the horse was as it had a reputation for being very fidgety and unfriendly, well after only 2 sessions the swelling had almost gone and she was back riding the horse. one woman actually commented that the day after the healing session the horse ran out in the paddock like a 2 yearold and it made the hairs on the back of her neck stand up to see such a sudden change in both the physical and mental state of the horse.
So until you learn more about the finer points of treating horses maybe just follow your intuition, remembering that reiki will find its own way to the areas that need it most.
hope this helps
good luck
namsate omshanti (Mike)