Abstract
Wildfires have recently increased in size and area burned and are projected to further escalate. Certain climatic conditions, such as increased temperature and decreased snowpack, create the ideal fuel conditions for wildfire ignition. As wildfires increase, so does the amount of ambient wildfire smoke. Among many pollutants found in wildfire smoke, fine particulate matter (PM2.5) is an ongoing health concern, as it is strongly associated with respiratory disease and mortality in humans. Relative to mature cattle, calves have developing lungs and immune systems that predispose them to respiratory disease, and therefore may make them especially vulnerable to wildfire smoke derived PM2.5 (wildfire-PM2.5). Recent research has shown that prenatal and postnatal exposure to wildfire-PM2.5 affects dairy calf health and metabolism, but it is unclear how early-life exposure affects health and development months later. My thesis research investigated early-life exposure of Holstein heifer calves to wildfire-PM2.5 and how that affects growth, pulmonary function, the immune system, and metabolism throughout the first year of age. We conducted a trial in which a group of calves was exposed to wildfire-PM2.5 in early postnatal life (within the first 2 weeks of age) and another age-matched group of calves was not exposed. We found that early-life exposure to wildfire-PM2.5 led to a brief period of compensatory growth after weaning, followed by a stunting of growth beginning at 26 weeks of age compared with that of unexposed calves. Pulmonary function was also affected; there was a delayed effect of lower tidal volume a few weeks after exposure. Reduced tidal volume coincided with increased lung consolidation, suggesting that accumulation of fluid and inflammatory products in the lung, because of exposure, negatively affects pulmonary function. However, the exposed heifers showed signs of pulmonary function recovery at 47 weeks of age. The heifers exposed to wildfire-PM2.5 also exhibited acute local inflammation in the lung, marked by changes in immune cell populations present in the lung. Acute systemic inflammation was also observed through changes in circulating leukocytes and an acute-phase response. There were differences between groups in circulating leukocyte counts at 39 weeks and 52 weeks of age as well, which may have been associated with changes occurring during puberty development. Shifts in blood metabolites were also seen at 12 weeks and 26 weeks of age, indicating possible changes in rumen development following exposure. Our results suggest that early postnatal wildfire-PM2.5 exposure in dairy calves elicits an inflammatory response, can negatively affect early pulmonary health and function, and restricts growth. Future research into reproduction and lactation performance after puberty would provide more insight into how early-life exposure to wildfire-PM2.5 affects heifer fertility and production.