fine particulate matter heaved into the atmosphere by wildfires can irritate lungs, raise respiration and heart rates, and diminish immune function.

Wildfires are nature’s way of renewing the landscape. However, Mother Nature’s wildfires have grown larger and raged longer in recent years, driven by larger reserves of stored fuel across the Western landscape. In 2022, over 90 large fires spread across seven Western states and dramatically reduced air quality.

Humans are advised to take caution when fine particulate matter climbs over 35 micrograms per cubic liter (PM2.5). During the peak of last fall’s fire season, air quality plummeted, almost reaching 300 PM2.5. While humans often could take shelter, animals, including dairy calves and cows, had to inhale the full brunt of that particulate-laden air.

“We still see effects up to seven days after air quality returns to normal levels, and that includes a reduction in milk yields,” explained Amy Skibiel, an assistant professor at the University of Idaho. “On day zero of the 2020 air quality episode, we have a drop of 1.5 kilograms of milk per day per cow,” said Skibiel, who studied the cows at the University of Idaho Dairy Center in Moscow, Idaho. That 1.5 kilogram drop in milk yield was based on a 100 (PM2.5) rise in particulate matter.

Pitiful air quality

“Remember, air quality diminished to almost 300 (PM2.5). So, multiply that 1.5 kilogram number times three,” she said, emphasizing milk production fell by 4.5 kilograms or 8 pounds per cow. The impact lingered even though air quality began to improve.

“Up to seven days later, we are still seeing a drop of 1.2 to 1.5 kilograms per day per cow for every 100 (PM2.5) increase in particulate matter,” said Skibiel at the 2023 Pacific Northwest Animal Nutrition Conference held in Boise, Idaho. “It’s important to keep in mind that this yield reduction due to compromised air quality is independent of the impact of temperature-humidity index (THI).

“In addition to reduced milk yields, we also found that milk protein concentrations were 0.14% lower for every 100 (PM2.5) elevation in particulate matter,” said Skibiel, who collected detailed data.

“Again, this situation persists for at least seven days after the last day of exposure. We did not monitor cows beyond that point of time. So, it’s possible that there are even longer-term effects. This is certainly an area of further research,” she explained.

“When it comes to metabolism, cows experienced decreases in blood urea nitrogen (BUN) and body condition score, but an increase in nonesterified fatty acids when both particulate matter and THI climbed at the same time,” said the lactation physiology specialist. “So, there is an interaction with PM and THI on metabolism. That could play a role in milk production and composition.

“Also, as particulate matter increases, there is a corresponding linear increase in blood carbon dioxide levels,” she said of compromised health. “That could be taking place because there could be an impact on gas exchange in the lungs. It could also just be a by-product of more smoke in the air. Remember, carbon dioxide is a component of smoke as well.

“Cows also experienced higher respiration rates when THI and PM levels rose,” said the Idaho researcher. “That’s a problem because the higher the breathing rate, the more particulate matter will be breathed into the lungs.”

The same situation holds true when looking at blood hematology data. We see reductions in red blood cell counts and hemoglobin with high particulate matter and THI levels. This reduces oxygen levels in the cow’s bloodstream and body.

“Interestingly, we did not see the effects until Day 3 . . . not on the first day of exposure,” pointed out the animal scientist, who collaborated with the University of Idaho’s Pedram Rezamand. “We also see, after three to five days, that there were higher eosinophil and lower neutrophil counts. That would be indicative of an infection or an immune response.”

Calves are another story

“It’s well known that there are critical windows where calves and other mammals are especially susceptible to environmental stressors. The preweaning period is one of those,” said Skibiel.

“We know that the preweaning period is absolutely critical in future performance. There are many studies that have shown compromised respiratory health in the preweaning period has negative impacts on their weight gain and lactation performance later in life,” said Skibiel, who studied the University of Idaho’s calves in depth during the 2021 fire season that had smaller fires over a longer period of time when compared to the major fires of 2020.

While fire’s impact on dairy calves has been rarely studied, there are other studies that one can draw upon.

“In monkeys that faced naturally recurring wildfires around 3 months old . . . wildfires had an immediate effect on lung function. Researchers also went back and looked at lung function in adulthood,” said Skibiel in reviewing the research. “Unfortunately, those monkeys were still having problems well into adulthood when they were exposed to wildfires in their infancy.

“In 2021, our lab enrolled 15 heifer calves into a trial during that summer,” she said. “The calves were housed in hutches in a barn at the University of Idaho Dairy Center that was fully enclosed on three sides and partially enclosed on a fourth side. Even with this building design, the calves were still exposed to the prevailing environmental conditions.

“Just like the cow study in 2020, we collected blood samples and took other measures of health on all the calves. When contrasting 2020 to 2021, there were multiple wildfire events during the calf study. That being the case, there were multiple spikes in particulate matter. THI events were rather consistent between the years,” she noted.

“When particulate matter and THI together were elevated, there was an increase in respiration and heart rates. Looking at hematology, we see decreases in white blood cells and neutrophils across the board. Again, that is an indication of an infection or an immune response,” she reminded the audience.

“Our research team also looked at calf health scores. We saw more eye discharge and coughing, and this means that these calves faced more ocular and respiratory irritation with the smoke. This took place after a three- to four-day lag with elevated particulate matter and THI,” she said.

“To summarize the effects we see in calves, there seems to be a decrease in overall population and circulation of immune cells. In these calves, we also saw fewer neutrophils in the blood, potentially because they are migrating to the lungs to fight inflammation,” she said of the calves housed in the nation’s third-largest dairy state. “During this time, we also saw elevated respiration rates . . . just like we do in the cows.”

What can be done?

“Our findings indicate it’s important to study these extreme weather events, including wildfires,” explained Skibiel. “Also, in the western United States, if we are only doing mitigation strategies for high temperatures and humidity, we are not doing enough.

“That begs the questions, ‘What are some practical solutions? How can we help our animals out during these wildfire outbreaks? What are some of the current recommendations to protect livestock during and after wildfires?’

“Before sharing that list, I want to add this disclaimer: These are vague and very general. Some of the recommendations are not feasible,” Skibiel recognized.

Monitor animals to see if they are off feed, if they are not drinking water, or if their eyes look awful, she began. That’s the moment you need to consult a veterinarian.

Limit exercise during periods of smoke. “This is probably the best thing you can do for animals right now. As we have shown, respiration rates increase when temperatures are high and when there is smoke in the air,” she said. “So, we don’t want to be doing anything to our animals that is going to require additional activity that will increase their respiration rate even more.”

Make sure animals have adequate water. “Hydration is really important in combating fine particulate matter. When the airways are moist, fine particulate matter can get trapped in mucus,” said Skibiel.

Keep animals indoors. “This comes back to the feasible situation,” said the practical professor. “It’s not really feasible, so we need to employ different strategies.”

Allow time for animals to heal. “Remember, the effects last for at least a week, if not months even after air quality has improved,” Skibiel said.

Good barn and field maintenance can help avoid or limit fires. “This strategy includes removing dead vegetative debris and other combustibles to prevent wildfires from starting in the first place or their ability to approach your property,” advised Skibiel.

Finally, have an evacuation plan prepared in case it is necessary to leave. The ability to act quickly during a natural disaster can help protect animals and humans from danger.