The diet of cows is an unpalatable story everywhere. In the last few decades cattle in Europe, including Britain, and the US have eaten human excrement, chicken manure, and even chickens.
They have, notoriously, eaten other dead cows. They have licked sump oil, chewed cement, and munched down plastic chippings as reusable roughage.
There have been claims from US groups that cattle have been fed dead cats and dogs, circus animals, hedgehogs, birds and other animals scraped from the roads.
In a business in which input costs have to be low and outputs high, grass and hay are no longer enough: for the past century, agribusiness has been looking for cheap proteins, fibres and fats to beef up output.
Some of it grows to hand: sheep and even cattle will eat seaweed and browse from foliage. But to produce high levels of protein in milk and cheese, or in meat, they need a high-protein, high-energy diet.
British farmers experimented with human and cattle excrement - heat-treated - two decades ago. This was possible as neither human nor cattle digestion is very efficient, so there is still a lot of nourishment even in manure.
There were other farm wastes to be recycled. Farmers struggled with the cost of disposing of dead animals. But even dead, these animals were nutritious.
So they began feeding cattle chopped up, heat-treated animal carcasses as a source of cheap crunchy protein at the beginning of the century. Both experiments came to a stop in the wake of the BSE epidemic.
Cattle feed in bags is required by EU law to state the categories of contents. There is no requirement to state the precise origin.