After you have consulted with a vet, you may use the following exercises to help your horse recover from his back pain. It’s very effective and relatively quick, and you can return to using the method at any time.
Set up heavy poles on the ground in a straight line, approximately 4 1/2 feet apart. You may have to increase or decrease the distance if the horse can’t manage this distance. It’s easiest to put the poles perpendicular to an arena fence, so that the horse can’t evade sideways. Try to use poles that won’t roll, either stabilized with an “X” of wood at each end of the pole, or with some other device to keep the polls still. If the horse kicks one, simply re-align it with the others. In the beginning, you will only be leading him through them at a walk.
Start walking him through the poles, using a bridle to gently pull his head down below the withers. Don’t wrestle with him or alarm him. Just calmly put your lead hand down toward the ground and exert steady pressure downward. When he allows you to lower his head, release the pressure on the reins. When you can reliably get his head down to perhaps knee level, begin to walk him through the poles at a steady pace. Go through them about 10 times each direction, walking steadily, but not hurriedly. If he kicks a poll, simply put it back in position. Don’t scold the horse, as he could be having trouble raising a leg high enough because his back is sore. After ten or so times successfully negotiating the poles, take him back to his stall. After a few days of this, if he’s not stumbling, and if you can lower his head from the saddle without using draw reins or other devices than the snaffle reins, you can ride him through the poles at the walk, and later at the posting trot. Be sure to wear a helmet. When this is going well, you may longe your horse through the poles if you can keep his head lowered toward the ground, at the walk and then at the trot. If he hops on a few poles, and doesn’t quit this after a few times through, you may need to shorten or lengthen the distance a little bit between poles. The exercise of going through the poles at walk or trot will stretch the long muscles of his back if you keep lowering his head. This stretches the muscles and allows them to loosen so that they will pulse as he moves. Work up to ten repetitions through the poles each way at the trot. After a week or two, he should be flinching much less when you palpate his back. You may continue this exercise, using it as a warm-up if you want, until the horse no longer palpates sore. The exercise is a wonderful warm-up for whatever work you want to pursue.