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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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What Drives Profitability in Farrowing? - Dr. Daniel Gascho

Video: What Drives Profitability in Farrowing? - Dr. Daniel Gascho


In this special episode of The Swine it Podcast Show Canada, marking World Veterinary Day, we welcome Dr. Daniel Gascho, swine production veterinarian and partner at Four Star Veterinary Service. He discusses how farrowing decisions must align with each farm's business model, why labor execution defines protocol outcomes, and how PRRS strategies should be tailored to each operation's health status and market position. Listen now on all major platforms!

"Protocols are only as strong as the labor that executes them, and that final step is what separates a plan on paper from results in the barn."

Meet the guest: Dr. Daniel Gascho / daniel-gascho-4a1bbb242 is a swine production medicine veterinarian and partner at Four Star Veterinary Service, based in Indiana. He focuses on individualized health strategies, vaccination planning, biosecurity, and practical protocol implementation across farrowing, nursery, and grow-finish systems.