It is not supposed to be capitalised when referring to a thoroughbred racehorse (or a standardbred), because, in the racing industry, this simply refers to whether or not a horse is purebred. Most of our readers are not horse breeders. The article mentions "thoroughbred" once, and "Thoroughbred" about 12 times. It should be the other way around. But in any case, capitalised or not, they're just as tasty.