November 15, 2021

During Oregon’s September 2020 wildfires—the worst in memory—dairy farmers told Jenifer Cruickshank, PhD, they were worried about the effects the smoke could have on their cows.

“The air quality was really awful for days and days, and I was getting questions from producers like, ‘What effect is this having on the cows?’” she said. “And I had to say, looking through the literature, ‘I don’t know that those questions have been answered.’”

Dr. Cruickshank is an assistant professor at Oregon State University College of Agricultural Sciences, and she works with dairies through the university extension service. She and Juliana Ranches, PhD, who is an extension beef specialist, started a three-year study this past summer into the effects of smoke exposure on cattle health and, for those in the dairy herd, their milk production.

A summary from the U.S. Department of Agriculture National Institute of Food and Agriculture, which awarded $37,000 for the study, indicates the researchers will conduct the study with 16 lactating dairy cows from the main dairy herd at Oregon State University’s campus in Corvallis and 16 beef cows at the Eastern Oregon Agricultural Research Center in Burns.

Another research team at the University of Idaho also has been analyzing the effects of exposure to smoke and wildfire-associated particulate matter on cattle health and milk production.

Amy Skibiel, PhD, assistant professor of lactation physiology at the University of Idaho Department of Animal, Veterinary, and Food Sciences, has been part of a team that collected data on the effects of smoke exposure on dairy cows at the university’s dairy center for the past two years and collected baseline data in summer 2019. She said preliminary results show some effects on immune cell populations in the blood—which suggest an inflammatory response—and a decline in milk production following exposure to heavy smoke originating from wildfires in California, Oregon, and Washington.

Even two weeks after the smoke event, the cows have not fully rebounded in terms of their milk production.

Amy Skibiel, PhD, assistant professor of lactation physiology at the University of Idaho Department of Animal, Veterinary, and Food Sciences

Drs. Cruickshank and Ranches said prior studies showed the effects of smoke exposure on humans, nonhuman primates, and laboratory mice. But neither found data specific to cattle or even more broadly to livestock.

A review article published in March 2021 in the open-access journal Animals indicates that authors from the University of Melbourne’s veterinary school similarly found little information on the effects of wildfire smoke on cattle exposed for extended periods. Unlike the health effects seen in humans, any effects in cattle are likely transient, they wrote.

“We conclude that cattle do not appear likely to be severely impacted by chronic smoke haze exposure, as evidenced by the lack of reports,” the article states. “We hypothesize this may be because cattle do not tend to suffer from the co-morbidities that, in the human population, seem to be made worse by smoke and pollution.”

Dr. Ranches said scientists want to characterize the health and production effects of smoke on cattle to help develop management strategies. Cattle exposed to smoke could be more prone to dehydration, she said, or they could benefit from feed supplements to bolster their immune systems.

Dr. Skibiel said that, in the University of Idaho’s study, a typical cow that had been producing 80 pounds of milk daily before smoke exposure produced about 3 pounds less per day afterward.

“Even two weeks after the smoke event, the cows have not fully rebounded in terms of their milk production,” she said.

Dr. Skibiel also is examining health and production records from dairies in the region, and she has secured participation so far from two in Idaho and one in Washington. Preliminary analysis of those data so far suggest associations between exposure to air with high particulate matter from wildfire smoke and increases in overall disease among dairy cattle and increases in calf mortality, as well as an unexplained correlation between increased exposure to particulate matter and increased mastitis.

Though dairy producers expressed concerns during Oregon’s September 2020 wildfires, they also told Dr. Cruickshank they hadn’t noticed any large declines in production, nor had they seen obvious clinical signs such as nasal congestion or coughing. Figures from Oregon State University’s cattle suggest exposure to wildfire smoke may have caused a small production decline, but Dr. Cruickshank noted that the decrease was still within the expected variation.

“Producers may not see that because it’s not a big, dramatic effect,” she said. “But having an understanding of what’s going on at the physiological level, we can understand the degree to which they’re affected.”

The Oregon team was able to collect baseline data on dairy cows in Corvallis in summer 2021, but the area lacked significant wildfire events over the summer that could be used to measure smoke exposure. In Burns, on the other hand, wildfires caused poor air quality since the beginning of summer, so the team was unable to collect the samples needed from beef cows to provide baseline data that are needed before collecting samples for smoke exposure data.

But these delays are built into the design of the three-year study, during which Drs. Cruickshank and Ranches expect at least one wildfire event will produce sufficient smoke to measure effects in each herd.