February 27, 2013

Feeding animals to animals: a call for vigilance against mad cow disease

Brent Kim

Brent Kim

Project Officer, Food Production & Public Health

Center for a Livable Future

Brain tissue affected by BSE

The World Animal Health Organisation (Office International des Epizooties, or OIE) recently recommended that the United States’ risk level for bovine spongiform encephalopathy (BSE) or “mad cow disease” be lowered from “controlled” to “negligible.” Secretary of Agriculture Tom Vilsack celebrated the recommendation as an achievement for beef producers, and for the federal and state agencies responsible for monitoring BSE.

The OIE’s recommendation is based on a review of efforts to manage the risk of disease. A positive report card on such matters is commendable, but I challenge the agencies responsible for food safety to do better.

As Drs. Love and Fry explain in a recent post, feeding animals to animals is a federally approved industry practice. Rendered animal carcasses, parts of animals (e.g. blood, bones, fat, and feathers), and animal excreta are commonly used as feed additives, primarily to cut costs. Some call this practice gross. Some call it recycling. Regardless, the practice can pose public health risks.

Using products of animal origin in feed can “recycle” contaminants such as arsenic, dioxins, and heavy metals back into the food supply chain, increasing their concentrations in animal tissues, and raising exposure risks among consumers.

Prions—the lethal infectious agents responsible for BSE in animals, and variant Creutzfeldt-Jakob disease (vCJD) in humans—pose particular concerns with regard to feeding animals to animals. Prions may be present in the brain, spinal cord, intestines, and other tissues of ruminant animals (cows and their ilk). Feeding these tissues to other ruminants can spread the infection among animals—and ultimately to people, who may be exposed to prions from eating contaminated meat (Cooking generally doesn’t help.).

To reduce the transmission of infectious prions, the FDA prohibits the use of specified ruminant tissues in human food, and in animal feed. These measures, however, are not fully protective. In 2012, the USDA confirmed a case of BSE in a California dairy cow—the fourth reported case of BSE in the U.S. (many others have likely gone undetected due to limited surveillance)—suggesting a gap in preventive measures.

While the estimated prevalence of BSE in the U.S. is very low, the potential for a widespread epizootic has been demonstrated in the United Kingdom, where more than 180,000 cases of BSE have been reported over recent decades. The UK outbreak has been implicated in human cases of vCJD.

To better protect against a similar scenario, the Consumers Union recently wrote a letter to the FDA, recommending additional measures to reduce the risk of prion transmission. The letter calls for expanded prohibitions on materials that can be fed to cattle, including bovine blood products and poultry litter, both of which may harbor infectious prions. Poultry litter contains spilled poultry food, which includes rendered cattle parts as ingredients, so in a roundabout way this amounts to feeding cattle to cattle.

Before the agencies responsible for food safety rest on their laurels, I urge them to implement measures to better protect against BSE, vCJD, and other health harms associated with the practice of feeding animals to animals. That would be another achievement worth celebrating.

Photo: Dr. Al Jenny, USDA.

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