Forbes Bird flu outbreaks have affected 34 dairy cow herds across nine states, causing some to question whether the use of contaminated poultry litter as cow feed may be the source of transmission, though experts say not enough is known to draw this conclusion.
Poultry litter (also known as chicken or broiler litter) is a mixture of chicken feces, feathers and bedding materials like sawdust, peanut hulls and pine shavings sweeped up from chicken coops, and typically used as a fertilizer and as feed for cattle, according to a study published in International Journal of Environmental Research and Public Health.
Though there are no federal regulations, some states like California ban the use of poultry litter as feed for lactating dairy cows—which are the only cows affected by the bird flu outbreaks circulating in the U.S.—but still allow its use in beef cows and other cattle.
Studies have shown chicken litter can harbor bacteria like salmonella and E. coli, so some experts worry the chicken litter feed cows eat contains traces of the bird flu virus, and therefore is the cause of bird flu outbreaks in cattle.
However, there’s not enough information available on how exactly cows contracted the virus from birds to draw this conclusion, Jodie Guest, the senior vice chair of the Department of Epidemiology at Emory University’s Rollins School of Public Health, told Forbes.
“We also do not have a good understanding of how common this practice is,” she said, so until it’s known how many of the affected herds use chicken litter as feed, “it would be really hard to link these two together.”
The Department of Agriculture said wild migratory birds are believed to be the root cause of the outbreaks, though it has confirmed infected unpasteurized milk may be causing cow-to-cow transmission.
Forbes has reached out to the Food and Drug Administration for comment. Poultry litter is used as feed among cattle because it’s a cheap source of protein, and an inexpensive way to dispose of the waste, according to the Department of Animal Sciences at the University of Missouri. The FDA initially discouraged the use of poultry litter as feed in 1967, but rescinded this suggestion in 1980 after extensive research was conducted and left the decision up to state governments. Once the U.S. reported its first case of bovine spongiform encephalopathy—or mad cow disease—the FDA placed a temporary ban on feeding cattle poultry litter in 2003 to prevent the spread of the disease. However, it later reversed this decision and instead prohibited the use of cow brains and spinal fluid—which are known to transfer mad cow disease—in chicken feed. This is because chickens have the potential to spread mad cow disease to cows via poultry litter if the birds ingest—and later excrete—infected cow brains and spinal fluid. The European Union and Canada have banned the use of chicken litter as animal feed due to the spread of diseases like mad cow disease.