Dr. Sue Dyson from England has developed an ethogram to determine pain in ridden horses.  An ethogram simply a catalog of behavioral signs in an animal and she indicates it is sometimes difficult to determine if a ridden horse is painful, so she developed and validated a catalog of behaviors that a horse might display under saddle when in pain.  She tested her ethogram using individuals with no specific training by using nerve blocks to numb painful areas and noted the responses of the evaluators before and after the numbing or blocking process.  

After much research, she cataloged 24 behaviors and indicated that if 8 or more of the 24 behaviors were present, the horse was likely in pain.  And although the ethogram was successful in identifying pain, training on the technique was required to better identify the lame and painful horses.  Potential pain-indicating behaviors on the facial area included ears rotated back, eyes closed or semi-closed, being able to see the sclera or white portion around the eyes, and an intense stare.  Also, opening the mouth regularly, exposing the tongue and moving it in and out of the mouth, and pulling the bit through the mouth to the left or right.  Body movements potentially indicating pain include repeated head position changes or head tilt, moving the head side to side, tossing the head and clamping, or swishing the tail.  Some gait abnormalities that can indicate pain include and irregular rhythm, hind limbs not following the front limbs, incorrect lead or gait changes, stumbling or toe dragging, spooking, reluctance to move, rearing and bucking.  All of these symptoms can occur due to many causes and not just pain but Dr. Dyson says if you see eight or more of these, musculoskeletal pain is likely and you should contact your veterinarian.