There are few horsemen who haven't had to deal with an old bow tendon at one time or another. You might get the horse when the bow feels as hard as a rock, but don't let it fool you. It can swell up and become mushy ever so easily. Once the swelling comes in then it immediately costs you. When the old bows become soft, then it's hurting the horse. A horse in pain will simply not race or perform at his optimum.
Keep the tendon as tight as possible. As long as you can keep it tight, then the horse will race well. If you back off from working on the leg, then you can kiss the money goodbye.
Here are a few pointers on how to treat:
1) The most important point is never to race the animal over his head. If anything, keep him down a bit in class. He should be racing where he's bringing in cheques every week, with little effort. If you're going to push the horse, then be prepared to have lots of trouble with the leg.
2) When the horse is just jogging during the week, keep lots of heat on the leg, (warm water ,hot paints ect.). This will allow the horse to heal any injury that occurred in the last race.
3) Prepare the animal properly for racing. Why should he feel pain? Certainly you would not want to hurt while in competition. Use lots of cold therapy 12-24 hours before the race.
4) This is the most important point. After racing always think that the worst has just happened, no matter what. Decide that the horse has just re-bowed. Give him some phenylbutazone, put the leg in cold water for an hour or so, put cortisone and DMSO on the leg and do him up in a cool cast. Give him two days off before returning to the track.
Remember that every time the old bow gets filling in it, then the inflammation has returned once a more. With each of these sessions, more and more scar tissue will enter the tendon proper. Eventually, what was once a tendon, becomes one big mass of scar tissue. No matter what you do at this point, the animal can simply not sustain any heavy work. For all intents and purposes, he's done racing or performing.