Jun 18, 2022
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Cows exposed to wildfire smoke produce less milk

Cows exposed to wildfire smoke produce less milk

In the past few decades, forest fires have been occurring more and more frequently around the world. In the US, wildfires burned 10.3 million acres in 2020, the largest area burned in a single year since 1960. Scientists predict that by the end of this century, the area burned annually by forest fires will increase by 76-152 percent.

Wildfire smoke inhalation is known to cause health and reproductive problems in humans, as well as impacting air quality, biodiversity and land use, but the impact of this environmental hazard on dairy cows has not been studied.

“Evidence suggests that wildfire smoke can lead to significantly greater exposure to harmful compounds than is typically seen in non-fire-related urban air pollution,” explained lead researcher Dr. Amy L. Skibiel, an expert in the Department of Animal Science, Veterinary and Nutritional Sciences University of Idaho.

Wildfire smoke contains fine particulate matter, which is a known air toxin and a major source of air pollution-related illness in humans. “Fine particulate matter can be inhaled deep into the alveolar cavities of the lungs, where it can cause inflammation, impair lung function, and be absorbed into the bloodstream,” explains Dr. Skibiel. However, the physiological response of dairy cows to fine smoke particles from forest fires has been largely unknown until now.

The research team observed 13 cows at the University of Idaho Dairy Center during the wildfire season from July to September 2020. Cows were kept in outdoor stalls and pens and were thus exposed to the atmospheric air. Fine particulate matter (PM2.5), air temperature and relative humidity were measured at a nearby monitoring station. Based on these measurements, the researchers determined that in mid-September, the cows were exposed to seven days of continuous exposure to high levels of fine particulate matter from wildfires. PM2.5 levels were 10 to 23 times the average 24-hour air quality limits set by the US Environmental Protection Agency.

Before, during and after this exposure, the daily milk yield of each cow was recorded, as well as the chemical composition of the milk. Before, during and after exposure, blood was taken from each cow from the jugular vein and analyzed for hematology, blood biochemistry and blood metabolites.

An analysis of these results showed that each cow produced an average of 1.20 to 1.55 kg of milk per day for every 100 µg/m3 increase in PM2.5 during seven days of exposure and seven days thereafter. Milk composition also depended on PM2.5 and temperature and humidity levels. The percentages of fat, milk protein and lactose were lower during periods of high solids and high temperature and humidity.

In addition, higher air temperature and humidity, combined with a large amount of fine particulate matter, altered protein and fat metabolism in cows, as well as reduced the population of immune cells in the blood of cows. The balance of essential blood minerals was also altered under these conditions, possibly due to sweating or the individual’s physiological response to stress.

White blood cells in the blood of cows have also been adversely affected during and after exposure to air pollution from wildfires. Cows and calves can suffer from respiratory diseases, which are the main cause of death in cases where the death was not caused by predators. Obviously, a decrease in the number of white blood cells (which are part of the immune system) may indicate a violation of the immune response and, thus, an increased vulnerability to respiratory infections.

This study is the first to examine the long-term and persistent effects of wildfire-induced PM2.5 emissions on dairy cattle immune response and lactation performance, and highlights the potential implications for dairy cattle welfare, farmer costs, and the supply of dairy products to the US population as increase in the frequency of forest fires against the backdrop of climate change.

The study was published in the Journal of Dairy Science.

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