I wonder if Ms. Riback has any statistics concerning how many horses from the great entertainment spectacle of horse racing actually end up leading happy retirement years. Not that this has anything to do with the problem!
Here is a personal question to those who think and act in the manner which is implied in Ms. Riback's post. For instance: Do you know anything about Utilitarianism? It is a philosophical theory of ethics (Jeremy Bentham and John Stuart Mill) that postulates an action is morally right, if it has consequences that lead to happiness. Thus, any society should aim for the greatest happiness of the greatest number. Today, I would suggest that this "greatest number" must be inclusive of all living, feeling beings. Are animals, other than human, happy working in the industry that seeks to entertain humans in whatever form? The very fact that you have a former racehorse negates a positive response to this question. Your horse can no longer entertain, so you have him or her. If you didn't have this particular horse, some animal, human or otherwise, would quite possibly be chowing down on him or her at this very moment.
I suggest we all have to "see" the larger picture.
(By the bye, I am not suggesting Utilitarianism as a viable or pragmatic approach to life. It is only one of many theories of ethics that exist, but it is useful in this instance. There are others that would suggest much the same.)