Cant go that far back, but in the 60s, I knew all the Lurcher owners, and a few Greyhound Lads from my town,
there was a Knackery that sold cooked Beef for dog food, they all bought this, and Sheep heids from the Butcher it was always mixed with brown bread, never complete, and most added SA50 supplement, the Lurcher Lads would also boil up Rabbit and Hare, the big difference to now, I never saw anybody feed raw, it was always cooked.