Dean over at Pullthepocket wrote an excellent blog entry regarding horse slaughter. I encourage everyone to take a look at it. If there is one thing which is going to cause harness racing to go the way of greyhound racing, it is the treatment of unwanted horses. These noble athletes are born to race and it is our responsibility that they don't end up in your dog's bowl or on a plate in France or Canada. Make no mistake, send a horse to an auction is worse than dumping your dog at the animal shelter, at least the dog will get a humane death.
If a person can not afford to take care of their horses when their career is done through adoption or if the horse is too lame, euthanasia, then they have no business owning a horse. It is up to the tracks and the industry to make sure these people are no longer in the game.
On the right side of the blog, there is a list of some standardbred rescue groups. If you race a horse now, research these groups and identify one you will use if the time comes to retire a horse which you can't afford to keep. Otherwise, do the right thing and pay for one last vet bill to euthanize the horse.