Premarin sounds like an innocent treatment which is offered to women as hormone replacement. It's made from PREgnant MARes urINe. Horses are bred, not for the foals, not for the joy of riding or companionship, but simply to "harvest" the pregnant mother horses's pee. And that, girls, is what goes into those hormone replacements. The brood mares, and the foals they produce, are nothing but a means to produce the money-making drug.
There are organizations who rescue, heal, and rehome these discarded, beautiful horses. Check out http://hope4horses.com, http://kisshorses.com. Read the story of Lazarus here: http://hope4horses.com/?page_id=66