Have you ever been to a farm store and seen the meds isle for equines? What animals do vets treat most besides dogs and cats? Feed lots for cattle as you describe them are a myth. The X-rays you get from the dentist or doctor are probably more harmful to your health than what trace of a chemical you get from your diet. The dietary laws were for good health nothing more and the people that observed them did not need to know an animal existed or not but were told to not eat the ones that did not meet a certain standard. Your knowledge of good food is as vague as your knowledge of dietary laws.If they tighten up the regulations of transport, farming and slaughter of the horses to make it more humane that there is no problem.
Also 'unclean' meat is only a religious idea and there are not scientific facts to say these animals are unhealthy for human consumption The religious books don't say anything about eating rhino, panda or polar bears - because the people who wrote the book did not know they existed, so how would we know if they are 'clean' or not?
I horse is not a 'bottom feeder'. It eats grass same as a cow! In fact a horse would be better for us that beef as they are not raised of huge cattle lots and fed a diet of corn, antibiotics and steroids.