Health & Wellness

USU Scientists Share Thoughts on Highly Pathogenic Avian Influenza in Cattle and Birds

By Lynnette Harris |

Avian influenza has been reported in dairy cows in nine states, but the virus is not fatal in cattle and pasteurized milk remains safe to consume. (Credit: USU/Bronson Teichert)

As the spread of Highly Pathogenic Avian Influenza (HPAI) from birds to dairy cows continues to unfold, Dr. Tom Baldwin, veterinary pathologist and director of the Utah Veterinary Diagnostic Laboratory (UVDL), wants people to remember a few key things.

“One of those things is that this virus does not kill dairy cows, nor is this an infectious disease that means the USDA has to implement mandatory slaughter,” Baldwin said. “It’s also not like some other viruses that cause more concerning problems like cows aborting their calves and it does not cripple a cow’s milk production long-term.”

Bruce Richards, assistant professor of animal science and USU Extension dairy specialist, adds that the public also needs to know that pasteurized milk and properly cooked meat are safe to consume.

Pasteurization destroys the influenza virus and other microbes in milk. Raw milk has not been through the high-temperature processing of pasteurization and carries a number of potentially dangerous microbes. Baldwin says the reason we began pasteurizing milk was to control the spread of tuberculosis.

“And since pasteurization kills those bacteria, it will certainly inactivate flu virus,” Baldwin said.

As of May 6, Colorado was the most recent state to report cows testing positive for HPAI. The American Veterinary Medical Association notes that there are 36 confirmed infected dairy herds in nine states, three of them adjacent to Utah — Idaho, Colorado, and New Mexico.

In late April, the U.S. Department of Agriculture mandated that dairy cows must be tested for HPAI within seven days of being transported across state lines whether they are going to another dairy or a livestock show.

What does HPAI look like in dairy cows?

Baldwin said one of the first things dairy farmers have noticed is a change in the cow’s manure. Most dairy cows have very loose fecal material. What farmers report is that infected animals’ manure becomes thicker. Cows also have a sharp drop in milk production.

Dr. Carmen Lau, a veterinary pathologist at the UVDL at Utah State University, noted that cows with the virus have a low-grade fever, their milk production decreases, and the quality of the milk changes, becoming thicker than normal.

The Utah Department of Agriculture and Food (UDAF) has information online about HPAI in cattle and poultry, including instructions about testing animals. A statement issued by Utah’s Assistant State Veterinarian Dr. Amanda Price says dairies that suspect cows may have the virus should move sick animals to a hospital pen and immediately contact their veterinarian.

In the case of some illnesses, farmers and dairy workers bring samples they have taken directly to the UVDL for testing. Baldwin says that is not the procedure for suspected cases of HPAI. The state covers the cost of the test, but samples must be collected by a licensed veterinarian or “an approved sample collector” who has received a case number from UDAF before collecting the required milk samples.

Cow Udder Anatomy 101

A cow’s udder is comprised of four separate glands. Each gland is called a quarter.

“It’s suspected that the virus is being spread by milking machines because they have found in some cows that only one quarter is affected instead of the whole cow,” Lau explains. “It makes us suspect that maybe some milking equipment is not self-cleaning the way it should, and it’s shooting infected milk into that quarter. We don’t have proof of that right now, but this virus isn’t showing any of the classic cow-to-cow transmission.”

For example, Lau says pathologists find almost no HPAI virus in nasal secretions, so samples from nasal swabs alone are not reliable for diagnosing the infection and secretions are not likely to be a means of spreading it.

Baldwin and Lau say that while being vigilant about animal health is important, they do not advise testing animals that are clinically healthy as a random surveillance of herd health.

“If you are selling cows that are going across state lines, you test them,” Baldwin says. “Or if it appears you have a disease outbreak, you need to test.”

Lau explains that testing healthy animals as a way of looking for disease is discouraged because it is not necessary and because it would consume large quantities of laboratory supplies that are needed to diagnose sick animals, especially if there were to be a large outbreak.

Still a Virus Primarily in Birds

A lot of attention is currently focused on cross-species infections, but the virus still primarily affects birds. While it’s technically possible for humans to become infected, Lau says that to date, even workers at poultry farms are rarely infected where there are confirmed cases of HPAI and large numbers of sick and dead birds.

Unlike HPAI in cows, the virus is deadly in chickens and some other birds. Ducks are commonly a host species spreading the virus but they often do not die from the infection.

Richards adds that wild bird mitigation and biosecurity practices are on the agenda for the free USU Extension Dairy Producer Field Day, on June 4, at the Cache County Fairgrounds.

Baldwin and Lau point out that there are other diseases to watch for in poultry.

When a backyard chicken owner finds a single dead bird and more do not die shortly after that, it likely was not caused by avian influenza. But in a flock of 25 birds, if a quarter or half of them die over a week, it is possible that HPAI is the cause. In some cases, the numbers are more drastic.

“When you suddenly find 20 of them dead in a day, that’s avian influenza,” Baldwin said.

He adds that hotter summer temperatures will likely reduce the number of infections because the virus does not thrive in very warm temperatures. Also, fewer migratory birds that transport the disease travel through and stop in Utah in the summer. However, the virus will not be gone, and there will likely be another surge of cases in the fall as more birds migrate and temperatures decrease.


Lynnette Harris
Marketing and Communications
College of Agriculture and Applied Sciences


Tom Baldwin
Utah Veterinary Diagnostic Laboratory

Carmen Lau
Professional Practice Assistant Professor
College of Veterinary Medicine

Bruce Richards
Dairy Specialist


Animals 92stories Vet Sciences 64stories

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