Assume No Animal Products Are Safe

By Karen Davis, PhD

Like all modern farmed animals, cattle suffer from many diseases because of how they are raised and fed with little known effects on the people who eat them and their products. Despite salmonella, E. coli, avian influenza, SARS, campylobacter and other evidence of farmed-animal-to-human disease transmission, government and industry reassure us that virtually no farmed animal diseases infect humans.

When a known transmittable infection is confirmed in a particular animal, as mad cow disease was confirmed in a cow in Washington state in December, they reassure the public there is nothing to worry about. It’s just “one animal”; the nation’s food supply “remains safe.”

But scrutiny belies these assurances. For example, on December 23, U.S. Agriculture Secretary Ann Veneman told reporters that the infected Holstein cow was never meant for the U.S. food supply (1) and, at the same time, that inspectors were trying to trace the whereabouts of the infected flesh (2). In fact, no one knows where it went. It could be, or it could have been, by now an ingredient in dog food, pig chow, poultry feed, hamburger, chicken nuggets or all of the above. It could be stewing in a sewage plant somewhere or “misfolding” in an individual’s neural pathway.

Talk about “isolated cases” is nonsense regardless. Agribusiness is global, and for this reason alone the synergies of animal and human diseases elude exactitude. However, we do know some things from which reasonable conclusions and choices may derive.

Take cattle feed, for example. Realizing that cattle get fatally infected with mad cow disease by eating feed containing tissue from the central nervous systems of infected cattle, and that a variant of this fatal neurological disease may be transmitted to human consumers of beef products, the U.S. and Canada banned certain cattle-derived feed ingredients from cattle feed in 1997 – brain, spine and the bones called vertebrae that protect the spinal cord.

However, nervous system tissue along with the stomachs and intestinal contents of poultry and pigs are fed to cattle (3), as are poultry manure and used poultry-house bedding, or “litter,” into which the birds excrete their waste, die prematurely and decompose by the millions each year (4). Cattle raised next to chicken houses are often “grazed” on this noxious waste (5).

Thus, even if feeding cattle to cattle is banned in the U.S. and Canada, feeding the banned cattle tissue to poultry and pigs is common and legal in both countries. Protein additives extracted from diseased cows and fed to chickens and pigs contain the same infectious prions that cause mad cow disease (6). When the birds and pigs who ate the prions are in turn fed to cattle, the infectious tissue is recycled back to its source.

If the danger of this circular disease route seems remote, consider that the prion proteins responsible for mad cow disease can withstand the intense heat that is used to render diseased cattle into poultry and pig feed (3), and that birds have been shown to have the same type of prion proteins as mammals, including humans (7).

For these reasons, the 2002 Nobel Prizewinning professor of biophysics at the Federal Institute of Technology in Zurich Switzerland, Kurt Wüthrich, warned last summer that chickens could be a “prion reservoir” that poses a “mad cow” threat to humans (7). Other distinguished scientists including D. Carleton Gajdusek, the first to be awarded a Nobel Prize in Medicine for his work on mad cow-like diseases (8), and Dr. Paul Brown, medical director for the U.S. Public Health Service, speculate that pigs and chickens could be harboring mad cow disease and passing it on to humans (9).

And while to date no pigs, chickens or turkeys have been reported with the disease, Michael Greger, M.D. of Cornell University says that these animals die so young, “they may not have time to develop symptoms,” yet they could act as “silent carriers” (10).

Knowing what we now know about mad cow disease and how it travels – including the fact that its travels cannot truly be traced, given the realities of the industrial economy – we should give serious thought to the role of animal products in our diet and that of our children. A vegetarian diet is not only an ethical opportunity to create a less violent world but an intelligent food safety initiative that doesn’t depend on the government.


(1) U.S. Reports First-Even Mad Cow Case, Associated Press & Canadian Press, Dec. 23, 2003.

(2) Sandi Doughton, Mad Cow Disease Suspected in Washington State, Seattle Times, Dec. 23, 2003.

(3) Kim Murphy, Canada May Step Up Its Livestock Controls, Los Angeles Times, May 30, 2003.

(4) Dennis Bueckert, If You Are What You Eat, then Canadian Cattle May Be Pigs or Chickens, Canadian Press, June 1, 2003.

(5) J Gerstenzang, Poultry Production Threatens Potomac River’s Health, San Francisco Chronicle, April 21, 1997.

(6) Fears over BSE in chicken, Vetscite (, June 5, 2002.

(7) Mad Chicken Disease? The Scientist (BioMedNet, July 25, 2003), July 30, 2003.

(8) Unconventional viruses and the origin and disappearance of kuru, Dec. 13, 1976. Quoted on NBC Dateline, March 14, 1997. Cited in Michael Greger, M.D., Mad Cow Disease: Don’t Just Switch to Chicken, Dec. 26, 2004.

(9) Fred Pearce, BSE May Lurk in Pigs and Chickens, New Scientist, April 1996: 5. Cited in Michael Greger, M.D., above.

(10) Michael Greger, M.D. Mad Cow Disease: Don’t Just Switch to Chicken, Dec. 26, 2003.


Karen Davis, PhD is the President of United Poultry Concerns, a nonprofit organization that addresses the treatment of domestic fowl in food production, science, education, entertainment, and human companionship situations and promotes the compassionate and respectful treatment of domestic fowl.