Dairy calves exposed to ambient fine particulate matter have increased bovine respiratory disease risk.

Even low ambient PM2.5 concentrations significantly increase BRD risk in preweaned dairy calves.

This retrospective observational study evaluated the association between ambient fine particulate matter (PM2.5) exposure and bovine respiratory disease (BRD) risk in 45 preweaned dairy calves in northern Colorado over an approximately 11-week period (May–August 2023). Calves were screened for BRD twice weekly using clinical scoring, yielding 900 total screenings that identified 27 clinical and 190 subclinical BRD events. Daily PM2.5 data were sourced from EPA monitors and analyzed using logistic mixed-effects models incorporating distributive-lag nonlinear models. Mean daily PM2.5 was 4.5 μg/m3, with peak concentrations reaching 54.3 μg/m3 during a wildfire smoke event. A 5 μg/m3 increase in PM2.5 was associated with a 66% increase in odds of incident BRD (OR 1.66; 95% CI, 1.08–2.53). Temperature-humidity index (OR 1.17) and male sex (OR 1.65) were additional significant predictors. Lagged analyses across a 0–30 day window demonstrated increased BRD odds at PM2.5 concentrations between 4.8 and 8 μg/m3—levels below current U.S. regulatory thresholds for human health. These findings suggest that even relatively low ambient air pollution levels may meaningfully elevate respiratory disease risk in young cattle. The authors recommend that veterinarians incorporate ambient air quality monitoring into BRD risk assessment and client advisory conversations. Prospective, multi-farm studies are needed to further characterize exposure-disease relationships and identify effective mitigation strategies.

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