287. Effects of Simulated Wildfire Smoke Exposure on Immune Indicators of Beef Heifers.

Abstract As climate change intensifies, the frequency and severity of wildfires are increasing, exposing livestock to harmful components of wildfire smoke, particularly fine particulate matter (PM2.5), one of the most concerning air pollutants. The impacts of wildfire smoke on cattle remain poorly understood, therefore, this study used a controlled wildfire smoke simulation to evaluate responses of beef heifers before, during, and after smoke exposure. In a two-year study, sixteen weaned beef heifers (Angus × Hereford; 8 months, 230 kg) were individually housed in pens inside a closed barn during a 36-day trial. The experiment consisted of three phases: baseline/acclimation (days −7 to 0), during which heifers acclimated to the environment; smoke exposure (days 1 to 7), where heifers were exposed to controlled simulated wildfire smoke daily for seven consecutive days; and a post-smoke exposure (days 8 to 28), where heifers were monitored for 3 weeks. During the smoke exposure, simulated wildfire smoke was generated each afternoon for seven consecutive days to intentionally reduce air quality. The air quality conditions were continuously monitored using two air quality monitors, with PM2.5 used as the primary indicator. Throughout the study, heifers had ad libitum access to alfalfa hay and water, and daily feed intake was recorded. Health scores were collected daily by trained technicians using the University of Wisconsin Calf Health Scoring System. Blood samples were collected weekly to evaluate physiological markers. In addition, animal behavior was continuously recorded throughout the experimental period. Preliminary data were analyzed over time using the MIXED procedure of SAS, with each heifer as its own control and year included as a random effect. Air quality, measured with PM2.5, changed over time (P ≤ 0.0001), reaching a daily average of 142 mg/m3 during smoke exposure, exceeding the EPA 24-h air quality standard for humans (35 mg/m3). Plasma immunoglobulin M (IgM; P < 0.001) and A (IgA; P = 0.06) concentrations changed over time. Plasma IgM concentrations were greatest during the baseline/acclimation (3.7 ± 0.30 mg/mL) and decreased following smoke exposure (d7; 2.38 ± 0.30 mg/mL), remaining suppressed through d14. Plasma IgM reached the lowest concentration on d21 (1.65 ± 0.43 mg/mL) remaining below baseline/acclimation concentrations (d28; 2.65 ± 0.30 mg/mL). Similarly, IgA concentrations were greatest during the baseline/acclimation (0.70 ± 0.26 mg/mL) and decreased following smoke exposure (d7; 0.59 ± 0.26 mg/mL), reaching the lowest concentration on d21 (0.54 ± 0.27 mg/mL) before partially recovering by d28 (0.59 ± 0.26 mg/mL). These findings suggest that wildfire smoke exposure may alter humoral immune response in beef cattle and highlight the importance of understanding climate-driven stressors in livestock production systems. This research was supported by the USDA-NIFA, Award #2023-68008-39173.