When I was training for the plod in 1988 we were informed that all pet food was required by Law to be fit for Human Consumption.The Canadian wheat thing I read here too last year about RAOC bread, because we had the facilities to store this particular type of flour it actually improved, Now commercial flours are chemically "improved". Manitoba flour springs to mind.
The cat/dog food thing is actually odd. Fast Food Nation said that cats and dogs were formally ingredients of pet food but there was uproar when it became known. It then was basically meat not fit for human consumption classification used , but have heard recently it was law change that meant they had to use meats/by-products fit for human consumption. The human emergency need may be a bit far-fetched but it is cheaper than other emergency options