Massive and devastating forest fires are a reality linked to climate change, now affecting numerous regions across Canada and the United States. Fires touch everything nearby: biodiversity, farmland, human health, and even livestock. The smoke that rises from these fires carries toxic compounds that can alter dairy production in cows. Inhaling the smoke has been shown to reduce milk output by about 30 percent.
This impact was documented in a study led by researchers from the University of Idaho and published in the Journal of Dairy Science. The researchers aimed to illuminate the side effects of large-scale fires beyond what is commonly understood.
“Smoke from wildfires exposes animals to far more harmful compounds than what is typically found in urban pollution,” explains lead researcher Amy L. Skibiel.
That expansive gray plume from forest fires contains the smallest particles, known as PM2.5. These particles measure about 2.5 microns and can reach the bronchioles and settle deep in the lungs. This danger had already been shown in a Nature Communications study, which found that forest fires raise the potential for inflammation and oxidative stress in the lungs more than urban pollution.
“Fine particles can be drawn deep into the alveolar spaces of the lungs, triggering inflammation, reducing lung function, and entering the bloodstream,” says Skibiel. Yet until now, researchers had not quantified what happens to cattle in these conditions.
During the second half of 2020, the East Coast of the United States faced one of its most dramatic droughts and heat waves, with drought conditions and fires burning millions of acres across several states. Meanwhile, a herd of Holstein cows grazed nearby Idaho, largely unaware of the environmental turmoil occurring a short distance away.
Less milk in cows for a week
Although the fires themselves did not threaten the cows directly, exposure to smoke from distant fires delivered poor air quality. For seven consecutive days in mid September, cows experienced fine particle levels that reached 10 to 23 times the thresholds recommended by the Environmental Protection Agency.
During that week, milk production declined. The effect persisted for seven days after exposure. Researchers attribute these metabolic changes to a combination of higher ambient temperatures, humidity, and a thinner atmosphere caused by the toxic particles. This blend of conditions altered the cows’ protein and fat profiles and affected their immune defenses.
The main trigger behind this disruption in bovine physiology appears to be stress. The research team cautions that more work is needed to understand the causes and consequences of electrolyte imbalance resulting from exposure to fine particles. The observed metabolic changes led to an approximate 30 percent drop in milk output.
In addition to animal welfare concerns, the study highlights potential challenges for the livestock industry if measures are not taken to reduce the impact of fires on air quality and farm operations.
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