杏吧原创

WHAT on earth are we feeding our farm animals? Farmers will apparently stop
at nothing in their quest for cheaper ways of producing meat, milk and eggs. And
that includes feeding waste and even sewage to livestock.

The practice can leave a nasty legacy. Cattle developed mad cow disease after
eating other cows鈥� brains. In Belgium, chickens fed waste put dioxin into the
human food chain. And the French feed their animals sewage. Pretty disgusting,
right?

Well, perhaps not. Global demand for meat, milk and eggs is booming,
especially in the developing world. We can never meet this demand by only
grazing animals on pasture. And if we feed them too much grain, people might starve
(see 鈥淧rotein at a price鈥�). The alternative is to feed them things
that humans cannot eat. So why not wastes? Indeed, why not excrement?

In the European Union, it is illegal to use sewage sludge in animal feed.
Last year, five French rendering plants were fined for hosing down their floors,
filtering out bits of carcass that had ended up in the waste-water treatment
system, and putting them back in the pot. Toilets at the plant flushed into the
same system but the results were sterilised. Was that so bad? Some animals eat
excrement naturally and pigs are still fed it on some cattle farms. True, the
BSE crisis showed us what happens when a pathogen recycled in feed isn鈥檛 killed
by sterilisation. We need precautions, such as not feeding a species its own
waste.

If you stay alert to dangers to human health, then feeding sewage to animals
is no more disgusting than the business of slaughtering them. Having killed the
beast, we ought to use as much of it as we can.

We should, of course, do what we can to make animal feed safer. In North
America, excrement from hen houses is fed directly to cattle, which thrive on
the protein and uric acid it contains. But occasionally a dead bird gets mixed
in, and this can give the cattle botulism. These risks would be avoided if the
waste were fermented as silage or pasteurised. But in the EU it is simply dumped
or burnt, as is the protein-rich bacterial sludge that grows in waste-water
treatment tanks. German researchers have found that pigs thrive on this
material, so wouldn鈥檛 this be a better use for it?

We need more of this research. The key is to work out how we can safely feed
waste to animals instead of burning or dumping it. As the demand for meat in
developing countries rises, farmers there are increasingly feeding chicken
litter, rendered carcasses and myriad other kinds of waste to their livestock.
These countries do not have the money to ensure that what they are doing is
safe. If people in rich countries can get over their repulsion, and decide to
replace some of the grain their own animals eat with waste, the safety research
is more likely to get done.

Feeding livestock on waste may be unpalatable, but it makes sense. After all,
which makes your queasier? Knowing your cheese came from a cow that dined on
sterilised chicken droppings鈥攐r knowing it came from a cow raised on grain
that could have fed a hungry child?