Abstract
IntroductionWildfire smoke degrades air quality across the United States, including major dairy-producing regions, largely through emissions of fine particulate matter (PM2.5). Although wildfire smoke is a well-recognized public health concern, its impacts on livestock health and productivity remain poorly characterized. This study evaluated respiratory function and immune and metabolic responses in lactating Holstein cows exposed to wildfire smoke.MethodsPrimiparous (n = 8) and multiparous (n = 13) cows housed in open-air freestall pens were monitored during the 2024 wildfire season (July-October). Sampling occurred opportunistically following naturally occurring wildfire smoke events. Environmental data, including PM2.5 concentration, air temperature, and relative humidity were obtained from a monitoring station located 5.7 km from the farm. Air temperature and relative humidity were used to calculate temperature-humidity index (THI). Daily milk yield (MY) was recorded. Blood, milk, and pulmonary function measurements, including tidal volume (VT), minute ventilation (VE), and respiratory rate (RR) were collected at three time points: 1 day after each of two separate 72-h wildfire smoke episodes (WF1 and WF2), and once two weeks later under low ambient PM conditions (LP). Blood hematology, metabolites, acute phase proteins, and milk composition were evaluated. At WF1 and LP, phagocytosis of granulocytes in whole blood was measured, and blood granulocytes and mononuclear cells were isolated for gene expression.ResultsWildfire smoke exposure altered breathing patterns, characterized by reduced VT and increased RR, while VE remained unchanged. Plasma haptoglobin concentration was greater at WF1 than at WF2 and LP. The proportion of phagocytosing granulocytes was higher at WF1 compared with LP, and expression of IL1B, CXCL8, TNF, and SELL was upregulated in circulating immune cell populations during WF1 relative to LP. Elevated PM2.5 interacted with THI to reduce MY on lag day 6 and 7. Milk fat percentage was lower at WF2 and LP, compared with WF1. Concentrations of plasma β-hydroxybutyrate and non-esterified fatty acids were greater at WF1 compared to WF2 and LP, whereas glucose concentration was reduced at WF1 relative to WF2 and LP.DiscussionAlthough stage of lactation likely contributed to some extent to these inflammatory and metabolic changes, the present findings demonstrate that even moderate wildfire-PM2.5 exposure is associated with altered pulmonary function and coordinated immune and metabolic responses in lactating dairy cows.