By Jared Strong

One of the largest dairy farms in the state — with a herd of about 10,000 in Sioux County — has cattle that are infected with avian flu, the Iowa Department of Agriculture and Land Stewardship reported Monday.

It is the seventh Iowa dairy herd with a confirmed highly pathogenic avian influenza infection. Five of those are in Sioux County, which has the most dairy cows of any Iowa county, according to U.S. Department of Agriculture data.

Infected herds are not culled like poultry flocks. While the virus is often fatal to domestic birds, affected cows typically recover within two weeks. Dairies suffer a temporary loss of production because the milk of sick cows — which contains large amounts of the virus — is discarded.

Investigations are ongoing to determine how the virus arrived in northwest Iowa, said Don McDowell, an IDALS spokesperson. O’Brien and Plymouth counties also have infected herds.

The virus is believed to have infected cows in Texas as early as December and spread to other states via the transportation of sick cows. It is likely spread locally by people and equipment that move between farms.

The virus has been identified in more than 100 herds in 12 states since late March, according to USDA data.

The avian flu variant that has been infecting cows was first discovered in Iowa in late May in a flock of 4.2 million egg-laying chickens in Sioux County. About a week later on June 5, testing confirmed the virus had infected an O’Brien County dairy herd.

Agriculture officials have implored dairies to increase their biosecurity measures and to limit visitors. The virus has been shown to transfer from dairy herds to poultry flocks and, in a few cases, it has infected people who work closely with sick animals.

Here is a timeline of highly pathogenic avian influenza infection reports in Iowa herds and flocks this year:

• May 28: A commercial egg-laying chicken flock in Sioux County with about 4.2 million birds.
• June 2: A commercial turkey flock in Cherokee County with about 103,000 birds.
• June 5: A dairy herd in O’Brien County with about 4,500 cattle.
• June 7: A dairy herd in Sioux County with about 250 cattle.
• June 12: A dairy herd in Sioux County with about 1,700 cattle.
• June 14: A dairy herd in Sioux County with about 1,000 cattle.
• June 14: A dairy herd in Plymouth County with about 3,000 cattle.
• June 15: A dairy herd in Sioux County with about 520 cattle.
• June 17: A dairy herd in Sioux County with about 10,000 cattle.

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