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U.S. Department of Agriculture detects second bird flu strain in dairy cattle

U.S. dairy cattle tested positive for a strain of bird flu that previously had not been seen in cows, the U.S. Department of Agriculture said on Wednesday, ramping up concerns about the persistent spread of the virus.

The H5N1 virus has reduced milk output in cattle, pushed up egg prices by wiping out millions of hens, and infected nearly 70 people since April as it has spread across the country.

Genome sequencing of milk from Nevada identified the different strain, known as the D1.1 genotype, in dairy cows for the first time, the USDA said. Previously, all 957 bird flu infections among dairy herds reported since last March had been caused by another strain, the B3.13 genotype, according to the agency.

Reuters reported news of the detection of the second strain on Wednesday ahead of USDA’s announcement.

The second strain was the predominant genotype among wild birds this past fall and winter and has also been found in poultry, the USDA said. It was identified in dairy cattle through an agency program that began testing milk for bird flu in December.

“We’re seeing the H5N1 virus itself be smarter than all of us,” said Beth Thompson, South Dakota’s state veterinarian.

“It’s modifying itself so it’s not just staying in the poultry and the wild waterfowl. It’s picking up a home in the mammals.”

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Biosecurity Compliance - Dr. Jean-Pierre Vaillancourt

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In this episode of The Swine it Podcast Show Canada, Dr. Jean-Pierre Vaillancourt, professor of veterinary medicine at the University of Montreal, discusses the human side of biosecurity compliance. He explains why protocols often fail when people are tired, unconvinced, undertrained, or working with impractical systems, and how leadership, employee input, technology, feedback, and small incentives can make biosecurity more consistent on swine farms. Listen now on all major platforms!

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Meet the guest: Dr. Jean-Pierre Vaillancourt is a veterinarian and professor of veterinary medicine at the University of Montreal. His work focuses on biosecurity, infectious disease control, and practical risk reduction in animal production systems, with experience across swine and poultry health. Learn more from Dr. Jean-Pierre Vaillancourt on The Swine it Podcast Show Canada, available on all major platforms.