Abstract
Wildfires have become more frequent and severe across the United States and globally due to a combination of factors. The smoke produced by wildfires is a complex mixture and one of the most concerning components is particulate matter 2.5 (PM 2.5). Despite the potential to harm livestock, research on wildfire smoke´s effects on health and performance is limited. In response to this gap in the literature, our group has developed a controlled indoor wildfire smoke simulation to evaluate the effects of smoke exposure on cattle performance, behavior, and health. In the first year of this study, eight heifers (Angus × Hereford, weighing 241 kg and 8 months) were individually housed in pens in a completely closed barn for 36 days. The study was segmented into three phases: acclimation, smoke exposure, and post-smoke exposure. The acclimation phase lasted from d-7 to -1, during which the animals adapted to their new environment. The smoke exposure phase occurred from d0 to 7, where the heifers were exposed to controlled smoke for seven consecutive days. The post-smoke exposure phase was from d8 to 28, where heifers were monitored for three weeks following smoke exposure. Throughout the study, blood samples were collected once a week (d -7, 0, 7, 14, and 28) for the evaluation of multiple blood parameters, and health scores were recorded daily. Heifers were individually fed alfalfa hay ad libitum, and feed intake was monitored daily. Behavioral data were collected 24/7 using four cameras, while air quality was monitored daily at one-minute intervals with two air quality monitors. Initial data from the first year of the study were evaluated using the MIXED procedure in SAS, with each heifer acting as its own control. Air quality, measured using PM2.5, exhibited changes over time (P ≤ 0.0001), with a daily average of 159 µg/m³ recorded during the smoke simulation phase, exceeding the EPA standard of 35 µg/m³. Feed intake increased over time (P≤ 0.0001) during the study, as expected for these growing heifers. Heifer plasma ceruloplasmin concentration peaked (P = 0.05) during the smoke exposure phase (29 mg/mL) and remained elevated (P = 0.39; 27 mg/mL) for one-week post-exposure before returning to baseline levels (23 mg/mL). Blood hematology showed an increase (P = 0.001) in lymphocyte percentage from d-7 (74%) to post-smoke exposure (d7; 83%), while the percentage of monocytes tended to decrease (P = 0.07; 8 vs. 5%) and neutrophil decreased (P = 0.02; 15 vs. 6%) in the same time frame. These initial findings suggest that poor air quality conditions similar to wildfire smoke can potentially trigger an immune response. This research was supported by the USDA-NIFA, Award #2023-68008-39173.