ABBOTSFORD – The devastation California dairy herds are experiencing from highly pathogenic avian influenza (HPAI) has BC dairy producers taking note.
There are no reported cases of HPAI-infected dairy or beef cattle in Canada to date, but with borders still open to the free movement of non-lactating animals and BC at the northern end of the Pacific flyway that includes California, the risk is real.
“The flyway that you have here and the poultry that has been decimated from it, I can’t believe you don’t have it and I think that’s great,” California vet Murray Minnema told the Mainland Milk Producers annual meeting in Abbotsford, January 17.
Minnema retired in 2019, but has been working with dairy producers since the initial outbreaks in early 2024 and wants BC farmers to have information in their toolbox.
Texas had the first identified cases of HPAI in dairy cattle in North America in February 2024. Minnema suspected the disease was in Idaho cows about a month later, a suspicion confirmed in early April. In August, the first cases were confirmed in California.
More than 950 US herds have been infected with the B3.13 strain as of early February 2025 and another strain, D1.1 which infected a BC teen, has now been discovered in cows through genome sequencing of milk in Nevada.
The initial cases were first mistaken for winter dysentery, but this didn’t line up with the symptoms of high temperatures, respiratory distress (including bloody or mucousy nasal discharge), manure with undigested feed, thickened yellow colostrum-like milk, lesions on vulvas, reduced feeding and lack of rumination.
“A very sharp veterinarian named Barb Peterson was standing under the eave of a milk barn when a stiff breeze came by and a bunch of dead birds blew off the roof,” Minnema says.
Peterson, a Texas vet, had the dead birds and farm cats tested and confirmed HPAI. The feline deaths were suspected to be from eating birds as well as ingesting contaminated raw milk.
“The standard number of cows that we saw that needed treatment were between 60% and 70%,” Minnema says.
Asymptomatic cows ruminate about 400 to 500 minutes a day. Prior to showing symptoms, rumination drops to 100 to 150 minutes.
“Just think about that,” Minnema says. “That cow is sitting there with a rumen full of feed and she’s ruminating about 20% of what she could be.”
Milk production of the first cows infected in California went from about 35 kilograms a day to 10 kilograms. As the disease progressed, the overall milk loss per herd was as much as half of total production.
“When you look at how the cow recovers from it within 10, 15, 20 days, that rumination comes back,” he says. “But look at that production. You don’t get your milk back.”
The pattern held for older cows as well as heifers. In an analysis of a 3,500-cow dairy over 120 days, mortality rates rose from 1.3% in non-infected cows to 6.8% in affected animals. Fever abortions also occurred regularly.
Cull rates among cattle that recovered were about 31%, underscoring the long-lasting effects.
Responding to the first signs of trouble is important in managing an outbreak, but Minnema warned that diagnosis is subjective.
“It’s not like we’re sitting there doing PCR,” he says. “You’ve got to lock up the animals, look at them, make a diagnosis and do a treatment. Over time, we’re pretty confident in making these diagnoses.”
When the disease began, milkers would mark cows with chalk if they saw the symptomatic yellowish, thick milk.
“You look at the chalk mark on their leg and then you just do a quick clinical evaluation of them. Are they dehydrated? If you had time, you would temp them,” he says.
The cows would be pulled from the main herd and treated, but there are no silver bullets when an outbreak happens. Production drops and the barn quickly becomes an animal hospital.
“These cows are extremely dehydrated, extremely stressed and they need rapid attention,” Minnema says. “We modified our plan and started drenching. That at least kept them going.”
Drenching included tubing sick cows with water and electrolytes. Minnema also recommended painkillers to ease discomfort.
“These animals are miserable and they need to be rehydrated and they need that temperature to go down,” he says. “And that rumen is just sitting there. You need to inoculate that rumen. You need to give them a binder. I fed a lot of charcoal.”
With the close proximity of poultry and dairy operations in the Fraser Valley, Minnema urged producers to be on the lookout for HPAI.
“If it’s in your neighbourhood, get a test on all your cows. Dry up as many cows as you can,” he says. “Because once you’re under it, you’re stuck and you’re going to be under it for anywhere from two to three weeks. After that, it’s a variable period of time as to recovery. I wouldn’t wish this on anybody.”
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