Triple-digit temperatures lasting for days and then weeks helped fuel a firestorm of highly pathogenic avian influenza A virus (HPAI A H5N1) cases on California dairy farms last summer.
“August wasn’t too bad, September was kind of rough, and then early October was severe,” recalls Dr. Maxwell Beal. “I think part of the problem was the cows had little relief from the heat even at night.”
But even with the onset of winter, Beal, with Mill Creek Veterinary Services, Visalia, Calif., adds that, “Cooler temperatures haven’t slowed the spread.”
Indeed, cases of the virus continue to trend upward in California. The state, the single largest producer of milk in the U.S., with 1,300 commercial herds and 1.7 million milk cows, holds the dubious distinction of being the current epicenter for HPAI H5N1.
As of Dec. 19, 2024, the California Department of Food and Agriculture had confirmed 650 dairy cowherds – roughly half of the commercial herds in the state – had been infected with the virus (see AHFSS - AHB - H5N1 Bird Flu Virus in Livestock - CDFA).
Bovine Veterinarian talked with several veterinarians in the Golden State and elsewhere about what their herds, producers and farmworkers have experienced and how they are addressing the virus. This is a summary of what practitioners shared.
Younger Dairy Animals Are Being Affected, As Well As Lactating Cows.
Among production animals on the dairy farm, lactating cows have taken the brunt of the virus infections so far, but that doesn’t mean other segments in cowherds aren’t or can’t be affected.
“I’m hearing reports from California veterinarians of sick young calves and challenges with cows resuming production and reports of dry cows aborting,” says Dr. Barb Petersen, owner and operator of Sunrise Veterinary Service, Amarillo, Texas. Petersen helped confirm the first case of HPAI H5N1 identified in U.S. dairy cattle last spring.
One of those reports came to her from Beal in California.
“I tell people, ‘Don’t sleep on your heifers, calves or your bulls, because there could be issues that we don’t know about yet simply because that’s not been our focus,’” says Beal, who reports that his virus-hit dairies have all experienced an uptick of abortions in first-calf heifers.
“One thing that happens at every affected dairy is we lose more calves, that were already called pregnant, and they’ll be all over the map as far as gestational age,” he says.
“It happens to dry cows, it happens to big calves, and these heifer abortions were all at 180- to 220-days (DCC), somewhere in there,” he adds. “Whether that’s directly caused by the bird flu or it’s caused by the clinical symptoms of the flu, I don’t know. And it’s the same for other veterinarians in our practice to the point that we will go back and reconfirm pregnant animals that we had already reconfirmed.”
Dr. Blaine Melody has had similar experiences: “We’ve consistently seen more early embryonic death and fetal loss at various days of gestation. We have recommended clients switch from long-acting dry cow tubes to lactating if we’re given the heads up before clinical outbreak, via early non-negative bulk tanks,” says Melody, a partner at Lander Veterinary Clinic, Turlock, Calif.
The Virus Amplifies Existing Health And Management Issues.
While HPAI H5N1 is associated with high morbidity and mortality in birds, this hasn’t been the case for dairy cattle in most regions of the country. Most affected animals reportedly recover with supportive treatment, and the mortality/culling rate has been low at 2% or less, according to the American Veterinary Medical Association.
That percentage fits with Beal’s experience in California, but dairy producers in some parts of the state have reported higher mortality levels. Some have experienced cow mortality rates as high as 15% or 20%, according to a Reuters article published in October. See Cows dead from bird flu rot in California
“Cows that get H5N1 are compromised, so any other health issues that are present in the dairy increase,” Beal explains. “Staph aureus, mastitis, mycoplasma, all of them go up.”
“The virus takes the problems that are already on your dairy that you’ve either figured out how to cope with or they’re just sitting at a low level, and it exacerbates them for probably a month,” he adds.
Melody says management quality plays a huge role in what producers and their employees must deal with when the virus hits.
“If you have overcrowded pens, bad cow comfort, poor nutrition management, poor transition cow management or any other underlying risk factors, you will have a worse outcome with a clinical HPAI outbreak. That’s a given,” he says.
In mid-December, California Gov. Gavin Newsom declared a State of Emergency to address the virus in California dairy cattle, ramping up monitoring, quarantine efforts, and resource deployment. See California Issues State of Emergency Warning in Response to More Bird Flu Found on Dairies
The number of farmworkers infected with the virus is likely higher than what’s being reported.
Officially, there have been 66 confirmations of human being infected by the virus in the U.S. See H5 Bird Flu: Current Situation
Melody, Beal and other veterinarians told Bovine Veterinarian they have seen presumed infected employees on farms working with cows.
“Some of these workers are at potential risk, because we don’t know all the ways this virus is spreading yet,” Melody says.
“They just put their heads down and work, so they can keep their paycheck,” Beal adds.
Drenching Cows Can Help, But Rest Can Do As Much Good In Some Scenarios.
Both Beal and Melody say drenching can help clinical HPAI cows, but veterinarians and their producers need a good plan for the treatment to work well.
Beal says there is a significant learning curve for people who have never or seldom drenched a cow. Employees on some of the infected dairies he works with went from never using the practice to suddenly treating hundreds and even thousands of cows a day.
In that intense scenario, Beal says it’s nearly impossible for employees to succeed.
“When you run a drench hose through 1,000 cows, you will not do as good a job with that last cow as you did with the first one,” he explains.
There is real potential to cause more harm than good to the animal physically, Melody adds.
“Drenching can help, but if you’re locking cows up too long or drowning cows because you’re drenching lots of cows and you’re exhausted, that undoes any good you’re trying to accomplish,” he says.
Beal says after working with a couple of outbreaks, he decided to try a different approach.
“We started to use a let-the-cows-rest approach, and I felt like we were still doing just as much good for the animals and not exhausting our staff in the process,” he says.
However, he continued to encourage workers to drench the ones that were clinically dehydrated or exhibiting signs of duress.
“I would say the ones that showed clinical signs to the degree that they warranted treatment has averaged around 30% in a herd,” Beal says. “The ones that are obviously clinically affected we need to treat, but not necessarily the ‘she’s got a runny nose,’ cows.”
What Is Your Definition Of Disease?
Melody says one of the challenges is how veterinarians and producers define disease as well as their definition of severity. With regard to HPAI H5N1, he has observed inconsistent practices and varied approaches to reporting, because people don’t have a consistent benchmark for reference.
“When you get HPAI on dairies, every cow that gets sick is then called a flu cow, but you can’t conflate that it’s all influenza,” he says.
Melody also encourages practitioners to keep a tight rein on their treatment protocols and to maintain consistent practices with regard to regulations.
“If you make things gray, when it comes to regulatory standards, we can quickly start to spiral, because you start going, ‘Well, we made this exception for this, so why not here too?’” Melody says. “Stay with your established playbook, and don’t deviate from it.”
Melody and Beal both say they have been frustrated at times by slow turnarounds by state laboratories responsible for providing test results. Their advice: Be a squeaky wheel with regard to getting virus test results.
“Many testing labs are overrun with samples, and the process gets bogged down, or the results don’t get to the veterinarian because of confidentiality rules,” Melody says.
“Some people are shipping animals that are infected but don’t know it because they didn’t get the information back in a timely fashion from the bulk tank tests,” Beal adds. “There needs to be a reworking of the testing protocols.”
Nutrition And Cow Comfort Practices Can Help Affected Animals Return To Good Production Levels.
Melody and Beal say most of their clients’ cows return to a good level of production post infection.
“Now, do they all come back 100%? No, I haven’t seen that on any of my dairies,” Beal says. “If people compare production now to last December, there’s likely a deficit. Some of the cows are ending up 5 lb. to 6 lb. under where they were this same time last year. That’s not unusual.”
Beal adds that veterinarians who can talk with their clients about what ramifications to expect from the disease, before it ever reaches their herd, can probably save a significant number of cows from being culled in the future.
What can improve that scenario for virus-impacted cows in the future is investing dollars in nutrition and facilities as farm resources permit, Melody adds.
“Renovate your dry cow barn, put some shade over those animals, put a little extra metabolizable protein into the fresh cows right now to make sure they’re getting off to a good start,” Melody advises. “Do good management, the things that you know are going to make your cows strong. Those things will pay for themselves whether you’re in the midst of a virus outbreak or wanting to help cows in the long-term.”
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‘No Established Gold Standard’
Dr. Blaine Melody, a partner at Lander Veterinary Clinic in Turlock, Calif., says somatic cell counts (SCC) are not a gold standard for defining parameters of the HPAI A H5N1 virus. He says SCCs can be wildly different for each farm because of management differences — whether dumping not dumping milk, sturdy versus frail cows, good or bad preexisting milk quality practices.
“My goal is trying to get as close to an apples-to-apples comparison between farms, and you can only decipher that by knowing the farms and asking more questions when people start throwing numbers around,” he says.
Melody offers one real-life example from his experience:
“Two dairies get HPAI at the same time,” Melody says. “One farm gets hammered with a 15% cow clinical mastitis case rate for the duration of the epidemic. The other farm may say it never had any HPAI clinical mastitis cows and only treated a handful of febrile cows with no milk, respiratory or GI disease. You look at their records and can confirm that to be ‘true.’ You ask more questions and also learn that the primary method of identifying mastitis is different between those two farms: the first farm strips and visually screens each quarter for abnormal milk, while the second does not and relies solely on milk conductivity sensors.”
“The vast majority of these clinical cows in our area are mild cases of mastitis with no effect on the udder or cow,” he adds. “This thick, clinical HPAI milk did not get flagged with conductivity sensors. Even within the same brand there can be modified settings farm to farm. The truth in this example ‘lied’ in the salable milk quality when their SCC more than doubled.
“The importance is understanding the farm management differences and knowing what further questions to ask rather than jumping at naked numbers that are often without clear denominators,” Melody says.
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200-Plus Mammal Species Infected
While researchers have learned a lot about HPAI A H5N1 since its confirmation in a Texas dairy herd in March 2024, much is still unknown, including the various ways the disease might spread and which animals it infects.
According to USDA’s APHIS, in addition to dairy cows, more than 200 other mammal species in the U.S. have been infected by the virus since 2022. One of the hardest hit animal populations on farms are barn cats, which often consume colostrum and raw milk, not to mention potentially infected birds and vermin.
Other U.S. mammals infected with the virus include a bottlenose dolphin, foxes, bobcats, mountain lions, coyotes, skunks, harbor and grey seals, opossums, squirrels, minks, otters, black bears, brown bears, polar bears, and a single pig on a backyard farm in Oregon, confirmed in late October.
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