There is some confusion around acupressure. What is it? It is really just the same as acupuncture, however the acupuncture points are stimulated in other ways e.g. by the hands with the same effect as when needles are used.
Acupuncture/acupressure is an ancient treatment, used at least 5000 years ago, and is said to have been used to treat animals for more than 3000 years. Literature from the 10th century describes acupuncture used to treat heatstroke in horses.
Acupuncture/acupressure is part of traditional Chinese medicine, and is based on the thought that we have a system of energy channels, called meridians, connected to the inner organs. The meridians may become imbalanced, and a therapist strives to re-establish balance in order for the energy to flow freely. Which means that a therapist does not treat diseases, but imbalances of the energy flow. The meridians cannot be seen, but has been located due to increased neuro electrical voltage. The neuro electrical voltage is even higher in an acupuncture point than along the meridians.
Research
In humans research has shown improvement of migraine, nausea, urinary tract infection, pains, infertility etc.
Personal experiences
Experiences I have acquired though treatment is that horses becomes calmer, less nervous and less quarrelsome.