POMC and Arthritis: Acupuncture Therapy/methods*, Adrenal Cortex/metabolism, Adrenocorticotropic Hormone/metabolism, Animals, Arthritis/therapy/veterinary, Electric Stimulation Therapy/methods*, Endorphins/metabolism, Horse Diseases/therapy, Horses/metabolism*, Hydrocortisone/blood*, Pain/veterinary, Pain Management, Pituitary Gland, Anterior/metabolism, Time Factors