In a recent development, epidemiologists are investigating how dairy cows in the Midwest became infected with a highly pathogenic strain of avian flu. As they search for answers, attention is being drawn to a common farming practice employed by thousands of farmers across the United States: the feeding of animal waste and parts to livestock intended for human consumption.

According to Michael Hansen, a senior scientist with Consumers Union, it is legal and common to feed chicken litter - the material that accumulates on the floors of chicken growing facilities - to cattle. This practice has come under scrutiny as it has been associated with previous disease outbreaks, including botulism.

Poultry litter consists of manure, feathers, spilled feed, bedding material, and even foreign objects like dead rodents, birds, rocks, nails, and glass. It can contain disease-causing bacteria, viruses (including H5N1), antibiotics, toxic heavy metals, pesticides, and other contaminants. Although California bans the feeding of poultry litter to lactating dairy cows, it remains legal to sell it as feed for beef and other cattle.

While the exact source of the avian flu infection in the cows is still unclear, the U.S. Department of Agriculture and the Food and Drug Administration have stated that it is "very unlikely, though not impossible" that poultry litter caused the bovine cases. However, the lack of federal regulations on poultry litter in animal feed raises concerns about potential food safety risks.

California's animal feed law requires that animal waste products sold for feed must not contain residues of pathogens, metals, pesticides, or antibiotics. The state's Department of Food and Agriculture's Feed Program conducts inspections of facilities manufacturing dried poultry litter and verifies treatment records to ensure compliance. However, it remains unclear whether there are regulations addressing the private exchange or production of poultry litter for feed outside of commercially sold feeds.

The controversy surrounding the feeding of poultry waste to cattle extends beyond California. Many states, including Missouri, Alabama, and Arkansas, lack regulations regarding contamination or processing of poultry litter. The federal government has also not taken regulatory action on poultry litter in animal feed, raising further concerns.

The practice of feeding poultry waste to cattle has drawn comparisons to the past concerns over mad cow disease in Europe. The exchange between cattle and poultry waste creates a potential route for prions, the agents that cause the disease, to re-enter the food supply. However, the FDA mandates the removal of prion-carrying tissues from poultry diets to mitigate this risk.

While the use of heated poultry litter feed in California is meant to kill bacteria and viruses, including E. coli and H5N1, research has shown that poultry litter can still carry antibiotic-resistant strains of E. coli. Samples from U.S. broiler chickens have been found to be resistant to multiple antibiotics.

As the investigation into the avian flu outbreak continues, the controversy surrounding the feeding of poultry waste to cattle raises questions about the potential risks it poses to food safety. The lack of comprehensive regulations and oversight at the federal and state levels has prompted calls for stricter measures to protect both animal and human health. It remains to be seen how this issue will be addressed in the future.