I worked in the greyhound kennels at brough park in the early nineties, and they were fed on a mixture of red meat, dry food, bread, two powders went into the mix, one was white and the other black, at a guess i would say they were bonemeal and charcoal, but could have been something else, this all went into a metal dustbin, which then went under a boiling pot full of meaty marrow bones, and when the tap was turned a light gravy came out, and the dogs were fed while it was piping hot and the food was well soaked, never saw any cowpats in their paddocks either