A mysterious illness that swept through dairy cows in the Texas panhandle in late January and early February worried dairy farmers around the nation, including Idaho.

A second wave of concern came over the industry when veterinarians traced it to highly pathogenic avian influenza, known by the initials HPAI. Even more worrisome: it was the same H5N1 strain that had been decimating poultry flocks in the U.S. since early 2022.

HPAI had never before been seen in dairy cattle, and no one knew for sure how it spread or what the outcome would be. It was just a matter of time before it started showing up in more herds in more states.

“Amid the concern, there was some relief that the illness had finally been identified and dairymen could begin to focus on effective treatments and prevention,” said Rick Naerebout, CEO of the Idaho Dairymen’s Association.

Most producers focused on their biosecurity protocols and did their best to prevent the introduction of bird flu into their herd, he said.

USDA confirmed the first detection of HPAI on March 25 in Texas. Within a week, the agency confirmed a dozen more cases in Texas, Kansas, New Mexico and Michigan.

As of Aug. 23, USDA had confirmed the virus in 192 herds in 13 states, with the latest cases reported in Idaho and Colorado on Aug. 13.

Colorado has been hardest hit, with the infection confirmed in 64 herds. Idaho follows with the virus confirmed in 31 herds.

While the flu is lethal to birds, it is not in cows. Most cows recover with supportive care, and the milk production loss is temporary.

Symptoms of HPAI in cattle include:

• Drop in milk production.

• Loss of appetite.

• Changes in manure consistency.

• Thickened or colostrum-like milk consistency.

• Low-grade fever.

Mystery illness

Before bird flu was diagnosed, reports were coming in from Texas that cows were dropping from 90 pounds of milk production a day to zero, Naerebout said.

In mid-March, his phone started ringing with calls from dairy producers around the state. The concern was whether milk production would return and whether pregnant cows would lose their calves.

“The unknown was scary,” he said.

But they learned from affected producers that milk losses were temporary, and the herd bounced back with the use of aspirin and water.

“Once we started to understand those things, it eased the nerves a lot,” he said.

It was a temporary disruption and producers would lose some money, but it wouldn’t put them out of business, he said.

“You can manage your way through to the other side,” he said.

Idaho’s producers focused on preventing it by enhancing their biosecurity procedures on the farm and having aspirin and water on hand.

Even before HPAI was confirmed in Texas, folks from Idaho Dairymen’s Association, Idaho Cattle Association and Idaho Farm Bureau met with the state Department of Agriculture about the mysterious disease. They determined the best way to protect Idaho’s herds was to stop importing cows from Texas. Not long after, the state also restricted importing cows from New Mexico and Kansas, other states where outbreaks had been reported.

However, shortly before that, a dairy producer in south-central Idaho had imported 105 fresh heifers, all from Texas.

Infection takes hold

The first case in Idaho was confirmed on April 2 in Cassia County, east of Twin Falls, on the dairy that had imported the heifers from Texas. They arrived March 8 or 9 and were likely from a dairy where cows had not yet been diagnosed or showing symptoms, said Dr. Scott Leibsle, Idaho’s state veterinarian.

The virus was confirmed in eight resident cows on the dairy, even though they had not been commingled with the new cows from Texas. At the time, Leibsle wasn’t sure how the infection made it to the resident cows but suspected cow-to-cow transmission. Alternatively, it could have been transmitted through manure or milking equipment, he said.

The source of the first single “spillover event” that introduced HPAI to dairy cattle — estimated to have occurred in Texas in early December 2023 — was migratory waterfowl. However, the spread between dairies is not attributed to migratory waterfowl, a USDA spokesperson said.

That spread was instead attributed to the movement of cattle between dairies and to normal business operations such as people, vehicles and farm equipment moving from an infected premise to others, the spokesperson said.

The outbreak in Idaho spread through the Magic Valley’s Minidoka, Jerome and Twin Falls counties. In late May to early June, it also showed up in the Treasure Valley’s Canyon, Owyhee and Payette counties.

These areas are the centers of the dairy industry in the state, Leibsle said.

It was also confirmed in Franklin County in the southeastern corner of the state.

State response

When the illnesses first surfaced in Texas and veterinarians didn’t know what the pathogen was, Idaho was the first state to clamp a full restriction on importing Texas cattle — dairy and beef.

Once the pathogen was identified, most states required testing of lactating dairy cattle seven days before crossing state lines, Leibsle said. Later, the federal government also mandated testing, so most states — including Idaho — backed off their requirements as redundant.

Federal requirements were handling interstate movement, quarantines were handling affected dairies in Idaho and there were no other restrictions on movement within the state.

The state’s priorities were to limit the spread of the disease and the movement of lactating cows, assist dairy producers with milk production losses and enable them to sell milk from healthy cows, Leibsle said.

The federal testing and reporting have generated data from across the country, improving USDA’s understanding of the virus. Additionally, the agency is using the latest data to learn about the virus and quickly contain the disease, the USDA spokesperson said.

Milk losses

While bird flu wasn’t as bad as producers first feared, it did impact Idaho’s milk production. Dairy Checkoff receipts were down 3.5% in May year over year and down 3.2% in June.

“Those are shocking numbers to be down,” Naerebout said.

That decline represents about 2 million pounds of milk a day. For perspective, the large Chobani Greek yogurt plant in Twin Falls processes 2.5 million to 3 million pounds a day.

Idaho’s milk production has only been down year over year twice in the last 30 years, during the economic downturns in 2009 and 2013.

With the prevalence of bird flu in some of the state’s dairy herds, Naerebout is expecting less milk production overall this year.

The impacts on individual herds’ milk production have varied in Idaho, from a 2% to 5% decline on the low end to 20% on the high end, he said.

“Our average dairy (2,500 cows) was losing $8,000 to $10,000 a day” because of the flu, he said.

The illness lasted two to four weeks in a herd. Veterinarians didn’t know why it lingered in some herds and not in others.

In addition, some cows left the herd due to bird flu or a secondary illness such as pneumonia and mastitis. Culling and illness caused an uptick in death loss while the virus was working its way through the herd.

“And we don’t have replacement heifers,” he said.

If replacements can be found, the price is about $3,000 a head.

“We don’t have the ability to turn up milk production like normal,” he said.

Flu underreported

USDA is encouraging testing in every way possible. The federal agency continues to work with states to provide every possible type of assistance as they consider actions in addition to those by USDA to further limit the spread between herds and contain and eliminate the virus, the USDA spokesperson said.

“Making sure producers understand the supports available, encouraging testing, deploying USDA to carefully investigate every new herd detection, and increasing our epidemiological understanding of this virus will help us reach our goal of eliminating this virus in the nation’s dairy herd,” she said.

But a lot of producers were still reluctant to get tested.

“What’s the upside? They know how to diagnose it and manage it,” Naerebout said.

Most of Idaho’s herds had already been through the illness before USDA announced reimbursement for production losses, and USDA trailed the industry in knowing how best to manage the outbreak, he said, adding that there was no upside to test and report it. The best source of information was peers.

In addition, there was and still are concerns about harming relationships with milk buyers and beef buyers, as well as USDA’s variability in response.

Movement restrictions

USDA initially chastised Idaho state officials for invoking import restrictions, he said.

“We went from that to USDA putting in even stricter animal requirements,” he said.

Producers were watching the escalation in USDA’s response and were concerned what USDA might do in the future, he said.

USDA was having producers whose herds tested positive fill out a 22-page epidemiology survey, testing cattle repeatedly and sharing information with the Centers for Disease Control and Prevention. The Idaho Department of Health and Welfare also wanted to interview and test employees, he said.

Managing on their own, producers had to triage their herds. There is only so much room in the hospital pen. The most severe cases were put in the hospital pen and their off-color or off-consistency milk was disposed of. The others went into the milking stream.

“We knew pasteurization was inactivating the virus. The virus is heat sensitive. FDA (U.S. Food and Drug Administration) testing confirmed that,” he said.

And it’s just common sense, otherwise there would have been a lot of sick Texans by the time bird flu was diagnosed, he said.

FDA testing of commercial milk found about 1 in 5 samples tested positive for HPAI viral fragments with a greater proportion of positive results coming from areas of infected herds.

The agency said the commercial milk supply is safe because pasteurization inactivates the virus and milk from sick cows is diverted or destroyed.

USDA tested retail ground beef in states with infected dairy cows, and all 30 samples were negative for the virus.

USDA also tested tissue samples and muscle meat from 96 condemned cull cows and one tested positive. Meat from condemned cows is prohibited from entering the food supply.

Vaccine development

Where government can help dairy producers is developing vaccines that prevent the flu. Idaho dairy producers are proponents of vaccination as an option to manage the disease, Naerebout said.

Vaccines haven’t been approved to control HPAI in the U.S., but they are used elsewhere as a preventive, emergency or routine measure.

More than 20 countries have used HPAI vaccination since 2005, the World Organisation for Animal Health reported in 2023.

Included on that list is China, Egypt, Mexico, Indonesia, Pakistan, Vietnam and Russia.

In October 2023, France began vaccinating its commercial duck population against HPAI. The move caused the country to lose market access for duck and foie gras in a handful of countries, including the U.S.

“USDA has work ongoing with vaccines for both poultry and bovines. Ultimately, we want to eliminate the virus and developing a vaccine to prevent another emergence of H5N1 in cattle will be an important step towards that end,” the USDA spokesperson said.

Vaccines for poultry are one part of USDA efforts to contain and mitigate the virus and it is pursuing their development, while keeping in mind a vaccination strategy would be challenging to implement domestically due to the wide distribution of birds, she said.

In addition, vaccines would have significant trade ramifications that would affect poultry farmers, and still might not be guaranteed to eliminate the virus.

“Having a vaccine to protect bovines, now that we know they are susceptible under some circumstances, could offer important protection for our dairy producers to blunt impact of the current or future outbreaks,” she said.

Slowing spread

Only one case of HPAI in dairy cows has been identified in Idaho this month.

“We had the surge in May and June,” state veterinarian Leibsle said, but it’s tough to say what’s ahead.

“We seemed to have peaked as far as dairies. I would also extrapolate that to the rest of the nation,” he said.

He puts duration of the illness in Idaho dairy cows at three to five weeks of lower milk production, and full milk production returned in every case.

Most of the affected dairies are out of quarantine, which requires two consecutive negative tests from all bulk milk tanks on the dairy.

While Idaho did lose cows, some dairy producers in Texas culled aggressively early on. Unfortunately for them, that wasn’t necessary, Naerebout said.

He doesn’t think the virus is still spreading in Idaho’s dairy herds. But if poultry is any indication, it’s going to be seasonal or reoccurring, he said.

“To us that indicates there’s a high probability this wasn’t a ‘one-off,’” he said.

Judging by the milk production losses in May and June, he thinks there were more Idaho dairies affected than the 31 USDA-confirmed positive cases.

Those who didn’t report an illness won’t be eligible for USDA reimbursement, he said.

“USDA is picking winners and losers depending on who played the game the way they wanted to see it played,” he said.

Interestingly, no bird flu cases were reported in Idaho’s neighboring states except for one case in Wyoming. It also hasn’t been reported in the two largest milk-producing states of California and Wisconsin.

“You only find it if you test for it,” Naerebout said.

With all the cattle movement in the West, Midwest and in an out of California, it’s hard to believe the No. 1 and No. 2 dairy states haven’t gotten it, he said.

Colorado: 64.

Idaho: 31.

Michigan: 27.

Texas: 24.

Iowa: 13.

Minnesota: 9.

New Mexico: 8.

South Dakota: 7.

Kansas: 4.

Oklahoma: 2.

Ohio: 1.

North Carolina: 1.

Wyoming: 1.

HPAI highlights

• Since Feb 2022, nearly 101 million birds have been infected in 1,173 flocks in 48 states. Of those, 508 flocks have been commercial and 665 flocks have been backyard, according to USDA.

• The World Health Organization reports a total of 891 cases of H5N1 in humans and 463 deaths in 24 countries from 2003 to May 22, 2024. Almost all were linked to close contact with infected live or dead birds or contaminated environments.

• As of Aug. 16, the CDC reports 13 cases in humans in the U.S. since April, four were associated with exposure to dairy cows and nine were associated with exposure to poultry.