Its there
Lots of corruption for sure. My best friend put some liniment on his horses ankles before a race once, and it turned out that another trainer had given it to him, it was laced, and after winning the race the drug test turned out positive for steroids. He lost all his customers and had to sell his barn. But, most trainers work the heck out their two year olds before races. Barbaro sat for five weeks before the Ketucky Derby, then only had two weeks before the Preakness, this type of training may have had something to do with everything that happened. As far as drugs in horses, if I remember right they are tested after every race. Sometimes before.
Give me a good pony horse over any thoroughbred, I exercised for a barn when I was a kid of fourteen (only weighted 90#), they had a old pony horse sitting saddled by the barn while the exercising/racing was going on. He would sit there slipshod, half asleep, until he was needed to catch a run away. That horse would launch, and could catch any thoroughbred in the field. He was getting up in the years, but was plain fast.
All I know is that the jockey for Barbaro did a hell of a job getting that horse stopped and off. Only met a couple of jockeys in my day, they were a breed of their own, tough little buggers. Had one show up for a owner to evaluate a horse. He showed up in a Caddilac, had his saddle and all his gear in the trunk. He saddled up this horse he had never ridden, and was only half warm, got a hand up, and handled this animal like they had been buddys all their lives. Unbelievable. I only exercised these horses for about a year, and had problems with arm strength at that time, had a little philly who hated me, she would drop her head and take off with me. The last time I rode her she put me through a fence rail, I quit... ... :-laf