Wildfires and smoke exposure
How does it affect livestock and how to prepare?
By Juliana Ranches
The risk that wildfires pose to people and the environment is increasing due to numerous factors, including, but not limited to, climate change. The most recent report from the Intergovernmental Panel on Climate Change (IPCC) indicates that weather conducive to wildfires (hot, dry and windy) has become more frequent in some regions and will continue to increase with greater levels of global warming (IPCC, 2021). Accordingly, eliminating the risk of wildfires is not possible, but much can be done to manage and reduce risks, such as creating a fuels management plan, defensible space areas, fire breaks, etc.
According to the National Oceanic and Atmospheric Administration (NOAA) and National Centers for Environmental Information, in the last few years, the number and size of fires have been above the 20-year average (7,000,513.55 acres; 68,707.25 fires; 103.92 acres/fire). In fact, 2020 was a record-breaking year, with the largest number of acres burned (10,274,679) and the largest number of acres burned per fire (176.37). Although most are not immediately endangered by wildfires, a larger population is affected by the resultant smoke, particulate matter, and other chemicals from combustion, which is carried by the air miles away from the center of ignition.
A recently published article reporting the findings of a survey conducted with more than 100 livestock producers in California, Nevada and Oregon shared the direct and indirect impacts of wildfires. Among the respondents, 26% reported they had to evacuate livestock, and 19% reported pasture losses as a direct impact of the 2020 wildfire season. Indirect losses from smoke exposure, including pneumonia and reproductive losses, were reported more broadly, but reduced weight gain and reduced milk yield were also reported by the producers (O’Hara et al., 2021).
As wildfires increase in frequency, size and duration, more humans and animals are exposed to the resultant wildfire smoke and the hazardous health effects. Smoke from wildfire is chemically complex, comprising a range of potentially toxic combustion products and fine particulate matter. The composition of smoke depends on factors such as fire behavior, vegetation type, season, burn conditions, available fuel, etc. The particulate matter (< 2.5 μm; [PM2.5]) is the major smoke product of concern. A mixture of solid particles and liquid droplets found in the air—is the principal public health threat of wildfire smoke.
Wildfire smoke contains several other hazardous components such as carbon monoxide, nitrogen dioxide, nitrous oxide, polycyclic aromatic hydrocarbons, ozone, sulfur dioxide, and hydrogen cyanide, etc. Air quality during wildfire events can be monitored using the air quality index (AQI).
The U.S. Environmental Protection Agency (EPA) establishes an AQI for five major air pollutants regulated by the Clean Air Act: ground-level ozone, PM2.5 and PM10, carbon monoxide, sulfur dioxide, and nitrogen dioxide. Specifically, for PM2.5, EPA standards suggest that the annual average should not exceed 15.0 µg/m3 or 35 µg/m3 over 24 hours.
Wildfire smoke exposure, impact on livestockIn a recently conducted study, our group evaluated changes in blood markers of cattle naturally exposed to wildfire smoke. Eighteen beef-on-dairy calves (Jersey ´ Simmental) from a commercial farm located in Vale (Oregon) were enrolled in this study at birth (May to June 2022).
Blood samples for analysis of cortisol (stress hormone), acute phase proteins (inflammatory markers), immunoglobulins, and pro and anti-inflammatory cytokines were collected before (June to August), during (September), and after wildfire smoke exposure (September and October), in a total of seven collections. Additionally, rectal temperature and health scores were collected from each calf at those time points. Air quality data, specifically PM2.5 near the study location, was obtained from the AirNow database.
Air quality before wildfire smoke exposure was considered adequate, and PM2.5 was, on average, 4.9 ug/m3 from June to August. In September, a wildfire event occurring approximately 10 miles from the study location reduced the air quality, increasing PM2.5 to an average of 44.6 ug/m3 for 4 consecutive days. After the fire was contained, air quality improved, and PM2.5 dropped to 8.6 ug/m3. Therefore, during the study duration, calves were exposed to 4 consecutive of poor air quality.
Blood cortisol concentrations of samples collected before smoke exposure did not differ (P = 0.89) at 4.4, 2.0, and 1.9 ng/mL (SEM:1.3). Blood cortisol concentrations increased (P< 0.001) and peaked during wildfire smoke exposure at 10.3 and 7.0 ng/mL (SEM:1.4). Immediately after smoke exposure, cortisol concentrations averaged 6.3 ng/mL, intermediate between those before and during wildfire smoke exposure (P = 0.89; SEM:1.3). Interestingly, in the last post-smoke exposure sample, blood cortisol concentration averaged 9.5 ng/mL, similar to concentrations during wildfire smoke exposure period (P = 0.99; SEM:1.3; Figure 1).
This increase in blood cortisol concentration post-smoke exposure was unexpected but likely explained by the calves having been weaned two days before this final sampling. Weaning is an essential procedure but has been reported to be stressful for the calves. Increases in blood cortisol levels have also been associated with poor livestock performance and increased susceptibility to diseases. Therefore, the increase in blood cortisol concentration as a result of exposure to wildfire smoke is concerning.
Immunoglobulin concentrations in plasma, specifically IgA and IgM, were also evaluated in the study due to their functions in the respiratory tract. The concentration of plasma IgA in calves exposed to wildfire smoke increased over time and peaked after smoke exposure (P= 0.001). The concentrations of plasma IgM increased from pre-exposure to during exposure (P = 0.001) and remained similar (P = 0.43) post-smoke exposure.
Collectively, the changes in immunoglobulin concentrations suggested an activation of the immune system and the development of an inflammatory response in calves exposed to wildfire smoke. Furthermore, alongside the elevation in blood cortisol concentration during exposure to wildfire smoke and changes in immunoglobulin concentrations, calves also exhibited alterations in health scores, including an increase in the percentage of calves exhibiting coughing and nasal discharge.
Colleagues at the University of Idaho recently reported similar findings from a study conducted during the summer of 2020. In that particular summer, a wildfire event near the research location (Moscow, Idaho) lasted for about seven days, resulting in daily PM2.5 concentrations up to 300 ug/m3. When evaluating the health scores of dairy calves, a few days after wildfire smoke exposure, nose discharge, more tearing from the eyes, and an increase in coughing were observed, potentially predisposing them to infections such as pneumonia.
In that study, the milk yield of Holstein cows was reduced due to exposure to wildfire smoke. The reduction in milk yield was observed up to seven days after the last day of wildfire smoke exposure. This reduction in milk yield, was reported to be approximately 3 lb per cow per day for every 100 ug/m3 increase in PM2.5 (Anderson et al., 2022).
The published literature on the effects of wildfire smoke exposure on livestock health and production is scarce; although a lot of questions remain to be answered, ongoing research efforts already demonstrated the negative impacts of wildfire smoke exposure on livestock health and production. Therefore, it is important for producers to recognize the importance of this environmental challenge and prepare accordingly. Planning and proactive actions are essential to reduce the negative impacts caused by wildfire and smoke exposure.
Tips on handling livestock during wildfire smoke exposureAccording to the American Veterinary Medical Association (AVMA), common signs of possible smoke or dust irritation in animals include but are not limited to: coughing or gagging, difficulty breathing, including open mouth breathing and increased noise when breathing, eye irritation, and excessive watering, nasal discharge, asthma-like symptoms, increased breathing rate, fatigue or weakness, disorientation or stumbling, reduced appetite and/or thirst.
Inflammation of the throat or mouth is also noticed when near to the wildfire. Although this is a long list, animals may show none of these signs and still experience stress from exposure to wildfire smoke.
During wildfire smoke exposure, monitor animal health daily, and if possible, keep track of feeding habits; distressed and sick animals often go off-feed. Provide livestock with plenty of fresh water strategically located near feeding areas.
Proper water intake is important to keep the airways moist and facilitate clearance of inhaled particulate matter. Dry airways allow particulate matter to remain in the lungs and airways, potentially worsening the symptoms of smoke exposure and eventually leading to opportunistic infections caused by bacteria as respiratory defense mechanisms are compromised.
Additionally, minimize animal exercise in order to reduce the flow of PM2.5 into the lungs, and when possible, postpone other stressful activities, such as vaccination, weaning, transportation and commingling until smoke clears. Those management practices are essential; however, known to be stressful and/or to elucidate an inflammatory response; therefore, postponing such practices to when environmental conditions are not challenging might be best.
ResourcesIPCC. 2021. Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change.
UNEP. 2022. Spreading like Wildfire – The Rising Threat of Extraordinary Landscape Fires. Nairobi.
Anderson, A., P. Rezamand, and A. L. Skibiel. 2022. Effects of wildfire smoke exposure on innate immunity, metabolism, and milk production in lactating dairy cows. J. Dairy Sci. 105:7047–7060. doi:10.3168/jds.2022-22135. Available from: http://dx.doi.org/10.3168/jds.2022-22135
Skibiel, A. L., A. Anderson, and P. Rezamand. 2023. Effects of wildfire smoke exposure in cattle : a review of the current state of knowledge and future directions. In: 2023 Pacific Northwest Animal Nutrition Conference Proceedings. p. 13.
O’Hara, K. C., J. Ranches, L. M. Roche, T. K. Schohr, R. C. Busch, and G. U. Maier. 2021. Impacts from Wildfires on Livestock Health and Production: Producer Perspectives. Animals. 11:3230. doi:10.3390/ani11113230. Available from: https://doi.org/10.3390/ ani11113230%0AAcademic
Ranches, J., G. M. P. Hernandez, A. R. Santos, M. Ferreira, and J. Cruickshank. 2023. Pre- weaned calves have increased cortisol levels post-wildfire smoke exposure. In: ASAS-CSAS-WSASAS 2023 Annual Meeting.
Ranches is an assistant professor and beef Extension specialist at Oregon State University.
