In the weeks since the unprecedented discovery of US cattle testing positive for highly pathogenic avian influenza (HPAI), some mainstream media outlets have attempted to connect this to the use of poultry litter in cattle feed.
However, those familiar with the science and with the workings of the US livestock and poultry industry find the idea rests on shaky grounds.
Experts believe cattle infected by wild birds
In a document published on 26 April, the US Animal and Plant Health Inspection Service (APHIS) stated “The genetic and epidemiological data indicate spillover of the virus from wild birds to dairy cows and some instances of spread from dairy to dairy and from dairy premises to poultry premises.”
This followed prior reports from APHIS that the earliest dairy cattle farms confirmed to have animals testing positive for HPAI reported finding deceased wild birds on their properties.
Moreover, the assumption that cattle were infected by wild birds is held by experts outside APHIS as well. In an early release version of a paper on H5N1 in domestic dairy cattle and cats published this week, researchers from Iowa State University’s college of veterinary medicine wrote that “feces from wild birds infected with HPAI virus [are] presumed to be the most likely initial source of infection in the dairy farms.” Additionally, a research team led by a biologist at the University of Arizona analysing the genetic sequences made available by USDA late last month has stated that “data support a single introduction event from wild bird origin virus into cattle.”
Litter does not leave HPAI-infected farms
It is also difficult to believe that the litter of a poultry farm could have become contaminated with HPAI without raising alarm bells that would have prevented it from being deployed elsewhere. “On a call last week, USDA’s chief veterinary officer and deputy administrator for veterinary services confirmed to stakeholders that nothing leaves the infected premises of an HPAI-impacted poultry farm, including poultry litter or waste to be used for crop fertilizer or feed,” shared Constance Cullman, President of the American Feed Industry Association (AFIA).
Could it be possible that litter leaves poultry farms before anyone is aware the flock had HPAI? This would rely on there being so-called “silent spread” of HPAI among US poultry flocks—and unlike in cattle, HPAI is not a particularly silent virus in poultry.
“I have seen no evidence that HPAI is spreading silently in chicken or turkey flocks,” Dr. David E. Swayne, one of the country’s preeminent experts in bird flu, told Feedinfo. “When they become infected, [they] develop clinical signs quickly and they die. So clinical signs and death are evident in the flock.”
Authorities have not imposed restrictions on litter
Dried poultry litter and waste are authorised for inclusion in feed by the Association of American Feed Control Officials (AAFCO)’s Official Publication. Such authorisations are the result of a process that is “extremely rigorous and transparent,” according to AAFCO Executive Director Austin Therrell. “It includes a scientific review by the Food and Drug Administration’s Center for Veterinary Medicine, as well as approval from a majority of state regulators. This regulatory pathway takes into account many potential food safety hazards to ensure that ingredients that gain approval can be safely and effectively marketed for use in animal food in the U.S.”
Beyond the ingredient review process, he added, there are also “extensive preventive food safety measures required for all animal foods by the Food Safety Modernization Act.” Manufacturers of processed animal waste products are required to test and maintain records to show that products like dried poultry litter do not contain pathogenic organisms such as Salmonella and E. coli, as well as other contaminants including veterinary drugs, pesticides, heavy metals, parasitic larva or ova, and mycotoxins.
It should be noted that US authorities have made no moves to curb or discourage the practice of using poultry litter as cattle feed (which is, in any case, understood to be rare by both AFIA and AAFCO). None of the recently-published requirements and recommendations from APHIS for the US cattle production industry mention feed, other than to warn against the use of milk from animals infected with H5N1 in feed for other animals, including calves or cats. Meanwhile, AFIA reports the FDA stating that it is "not aware of any data showing that the use of poultry litter in cattle feed is posing human or animal health risks that warrant restrictions on its use."
