Excerpt:
October 4, 2024
‘More serious than we had hoped’: Bird flu deaths mount among California dairy cows
Since the end of August, the Central Valley has suffered multiple heat waves, with daytime temperatures exceeding 100 degrees.
“Heat stress is always a problem in dairy cattle here in California,” he said. “So you take that, you add in this virus, which does have some affinity for the respiratory tract ... we always see a little bit of snotty noses and heavy breathing in animals that are affected ... and for some of them, just the stress takes them.”
Indeed, most of the deaths are not directly the result of the virus, he said, but are “virus adjacent.” For instance, he has seen a lot of bacterial pneumonia, which is likely the result of the cow’s depressed immune system, as well as bloat.
Although dairy operators had been told to expect a mortality rate of less than 2%, preliminary reports suggest that 10% to 15% of infected cattle are dying, according to veterinarians and dairy farmers.
“I was shocked the first time I encountered it in one of my herds,” said Maxwell Beal, a Central Valley-based veterinarian who has been treating infected herds in California since late August. “It was just like, wow. Production-wise, this is a lot more serious than than we had hoped. And health-wise, it’s a lot more serious than we had been led to believe.”
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He said that when the cows aren’t feeling well, they often don’t eat.
“The digestive tract, or rumen, basically requires movement. There has to be things moving out of that rumen constantly in order for the pH balance and microbiome to stay where it should be,” he said. So, when they’re not eating, things in the digestive tract stagnate.
That, in turn, causes them to “asphyxiate because their diaphragm has too much pressure on it.”
In addition, he and others are seeing a lot of variation in the duration of illness.
Although early reports had suggested that the virus seemed mild and lasted only about a week or two, others are seeing it last several weeks. According to the industry newsletter, at one dairy, cows were shedding the virus 14 days before they showed clinical signs of illness. It then took three more weeks for the cows to get rid of the virus.
They’re also noticing the virus is affecting larger percentages of herds — in some cases, 50% to 60% of the animals. This is much more than the 10% that had been previously reported.
Some say the actual rate may be even higher.
“I would speculate infection is even higher; 50[% to] 60% are showing clinical signs due to heat stress or better herd monitoring earlier in infection. Unfortunately, few or no herds have been assessed retrospectively through serology testing to determine actual infection rates,” said John Korslund, a retired U.S. Department of Agriculture veterinarian epidemiologist.
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https://www.latimes.com/environment...deaths-increasing-among-california-dairy-cows
