Dairy Cattle and Bird Flu

One of the early hints that the virus could be spreading through a route other than contact with infected milking machines, Lombard said, was that the virus was spreading through herds quickly, more quickly than would be the case with machine-based spread.

Another clue, he said, came from identifying that antibodies for the virus were first showing up in cattle’s bloodstream prior to detection in the milk. That finding, he said, suggested cattle were being exposed to the virus by a route other than from contact with infected machines.

Lombard is now in the process of collaborating with members of CSU’s Department of Atmospheric Sciences to try to better understand the potential for airborne spread. The researchers are attempting to match wind patterns to dates of infected farms from a recent outbreak in California, which could support the theory that the virus moves through the air. Another possibility, he said, is that the virus is being carried from farm to farm via another species, such as birds.

In addition to learning about how the virus spreads, there have been other initial takeaways from the sampling done by Lombard’s team. Notably, he said, they detected the virus intermittently, which can make the virus more difficult to track because an animal might not test positive one day but might still be shedding the virus. Generally, Lombard said, cattle also appeared to shed the virus for a particularly long period, in some cases more than 10 weeks.

Lombard said the team’s sampling also revealed that cattle could shed the virus up to seven days prior to showing clinical signs — a so-called “subclinical” period similar to how COVID-19 behaves in humans. “By the time you have clinical signs,” Lombard said, “it’s everywhere.” In addition to decreased milk production, the most common clinical signs, he said, have included nasal discharge, decreased feed intake and inflammation of the mammary glands.

Notably, Lombard said, the cattle they tested in Colorado showed a strong antibody response to the virus, suggesting that an avian influenza vaccine could be effective in dairy cattle.

In addition to sampling cattle, Lombard’s team also sampled for the virus on trucks that transport milk from the farm to production facilities. They found a single positive, he said, suggesting milk trucks are not a high risk for spreading the virus. 

Strong student effort

To accomplish the extensive sampling throughout the summer and fall, Lombard enlisted the help of 17 students, including multiple undergraduates, from the College of Agricultural Sciences and the College of Veterinary Medicine and Biomedical Sciences. The team collected nasal, urine and blood samples from 30 to 40 cattle weekly at five Colorado dairy farms. They also collected milk samples biweekly.

Sami Smith, a first-year student in CSU’s Doctor of Veterinary Medicine program, had been working with the CSU AgNext research intern program during the summer when she learned about the opportunity to contribute to Lombard’s avian influenza sampling project. “This was a very big project,” Smith said. “I was really excited to join and help out.”

Smith had not worked with dairy cattle before, but she was headed into her first year of vet school and had an interest in large animal medicine, so the project was a good fit. The sampling days were long and often started early. She would sometimes wake up at 3 a.m. so the team could be sure to catch the same cattle for sampling and avoid the afternoon heat.

Still, even on those early mornings, Smith found the work rewarding. “It was pretty exhausting,” she said. “But our team was great; I feel like we really understood each other. I learned a lot about how a team works.”