Effects of wildfire smoke PM2.5 on indicators of inflammation, health, and metabolism of preweaned Holstein heifers

Abstract

Wildfires are a growing concern as large, catastrophic fires are becoming more commonplace. Wildfire smoke consists of fine particulate matter (PM2.5), which can cause immune responses and disease in humans. However, the present knowledge of the effects of wildfire PM2.5 on dairy cattle is sparse. The present study aimed to elucidate the effects of wildfire-PM2.5 exposure on dairy calf health and performance. Preweaned Holstein heifers (N = 15) were assessed from birth through weaning, coinciding with the 2021 wildfire season. Respiratory rate, heart rate, rectal temperatures, and health scores were recorded and blood samples were collected weekly or twice a week for analysis of hematology, blood metabolites, and acute phase proteins. Hourly PM2.5 concentrations and meteorological data were obtained, and temperature-humidity index (THI) was calculated. Contribution of wildfires to PM2.5 fluxes were determined utilizing AirNowTech Navigator and HYSPLIT modeling. Mixed models were used for data analysis, with separate models for lags of up to 7 d, and fixed effects of daily average PM2.5, THI, and PM2.5 × THI, and calf as a random effect. THI ranged from 48 to 73, while PM2.5 reached concentrations up to 118.8 µg/m3 during active wildfires. PM2.5 and THI positively interacted to elevate respiratory rate, heart rate, rectal temperature, and eosinophils on lag day 0 (day of exposure; all P < 0.05). There was a negative interactive effect of PM2.5 and THI on lymphocytes after a 2-d lag (P = 0.03), and total white blood cells, neutrophils, hemoglobin, and hematocrit after a 3-d lag (all P < 0.02), whereas there was a positive interactive effect on cough scores and eye scores on lag day 3 (all P < 0.02). Glucose and NEFA were increased as a result of combined elevated PM2.5 and THI on lag day 1, whereas BHB was decreased (all P < 0.05). Contrarily, on lag day 3 and 6, there was a negative interactive effect of PM2.5 and THI on glucose and NEFA, but a positive interactive effect on BHB (all P < 0.03). Serum amyloid A was decreased whereas haptoglobin was increased with elevated PM2.5 and THI together on lag days 0 to 4 (all P < 0.05). These findings indicate that exposure to wildfire-derived PM2.5, along with increased THI during the summer months, elicits negative effects on preweaned calf health and performance both during and following exposure.

Keywords: acute phase response; air quality; dairy calf; hematology; inflammation.

Figure 1.

Average daily PM_2.5 concentrations and THI from July 1 to October 1, 2021, which encompassed the duration of the study period. There were multiple wildfire events over the course of the study period, resulting in spikes in daily average PM_2.5. Purple squares indicate THI and green circles represent PM_2.5. Yellow stars below the x-axis indicate dates in which samples were collected.

Figure 2.

Maps of active wildfires, PM_2.5, and air mass trajectories on two separate days. (A) A day with wildfire smoke present (August 13, 2021), resulting in a 24-h average PM_2.5 concentration of 118.75 μg/m³. (B) A day without wildfire smoke present (August 29, 2021), resulting in 24-h average PM_2.5 concentration of 3.42 μg/m. AirNow-Tech Navigator (https://www.airnowtech.org) mapping system was used to produce the maps, with NOAA HYSPLIT atmospheric transport and dispersion modeling system utilized to visualize air mass trajectories. Air masses are shown as 72-h backward trajectories, at atmospheric heights of 50, 100, and 150 m (green, blue, and red lines, respectively). Colored dots indicate ranges of PM_2.5 concentrations at monitoring stations. HMS indicates Hazard Mapping System, with smoke plumes and wildfire locations displayed. The yellow star depicts the location of the University of Idaho Dairy Center where the research was conducted.

Figure 3.

Interactions between fine particulate matter (PM_2.5) and temperature–humidity index (THI) at lag day 0 on (A) calf respiratory rate (RR), (B) heart rate (HR), and (C) rectal temperature (RT). Preweaned Holstein heifer calves (N = 15) born in July of 2021 were naturally exposed to wildfire smoke multiple times throughout the summer. Respiratory rate was increased as a result of PM_2.5 and THI interactions (P = 0.04). PM_2.5 and THI had a positive interaction on heart rate (P < 0.001). Rectal temperature was increased due to the positive interaction of PM_2.5 and THI (P = 0.04).

Figure 4.

Interactions between PM_2.5 and THI at lag day 3 on (A) total white blood cell count, (B) neutrophil count, (C) hemoglobin concentration, and (D) hematocrit. Preweaned Holstein heifer calves (N = 15) born in July 2021 were naturally exposed to wildfire smoke multiple times throughout the summer. Total white blood cell count was reduced after exposure to elevated THI and PM_2.5 together (P = 0.01). PM_2.5 and THI interacted to decrease neutrophil count (P < 0.01). Hemoglobin concentration was decreased as a result of the interaction of PM_2.5 and THI on lag day 3 (P < 0.0001). Combined increased PM_2.5 and THI resulted in lower hematocrit (P < 0.0001).