You are what they eat.(animal feeds)

Humans are at the top of the food chain. As a result, we're vulnerable to pathogens, drugs, and contaminants consumed by the animals we eat. And we eat a lot: an average of 137 pounds of beef, chicken, fish, and shellfish per American in 2002, the latest year for which figures are available.

Food animals used to eat what grew naturally--grass and grain for cows and chickens; small fish or other sea life for big fish. But life on today's farm--often a 30,000-cow feedlot or a 60,000-chicken coop--isn't so simple. The need of such facilities for huge quantities of high-protein rations and the need for slaughterhouses to find a cheap, safe way to dispose of waste gave rise to a marriage of convenience between renderers and food producers, and to the inclusion of animal by-products in animal feed.

The pairing was seen as a boon: Waste was recycled into needed protein and other nutrients for animals. But the addition of the rendering industry to the animal-feed mix has meant more trouble controlling and monitoring feed production, more vulnerability to problems, and another layer of regulation.

To assess the safety of the nation's animal feed and implications for consumers, we interviewed feed-industry experts and critics; reviewed recent research and spoke to scientists who conducted it; and tested chicken for arsenic, an approved additive in an antiparasitic drug given to many healthy birds to make them grow faster.

We asked feed-company executives to talk with us, but only representatives of fish-feed makers and the heads of four feed trade associations were willing.

Our investigation raises concerns that the federal government isn't doing enough to protect the feed supply and that as a result, the food we eat may not be as safe as it could be: Regulatory loopholes could allow mad cow infection, if present, to make its way into cattle feed; drugs used in chickens could raise human exposure to arsenic or antibiotic-resistant bacteria; farmed fish could harbor PCBs and dioxins.

WHAT THEY EAT, AND WHY