Studies by the U.S. Department of Agriculture's Agricultural Research Service indicate that the dust stirred up by wind and restless cattle at dairies does contain bacteria, fungi and small bacterial remnants such as endotoxins, but these potentially problematic particles are not found at high levels far beyond the barnyard.
ARS microbiologist Rob Dungan is investigating dispersal patterns and transport of these bioaerosols at the ARS Northwest Irrigation & Soils Research Laboratory in Kimberly, Ida.
In the western U.S., dairy cows are kept in outdoor pens or in a combination of exercise pens and barns at open-freestall facilities. Residents in nearby communities want to know if their proximity to these facilities increases the potential risk of exposure to airborne microorganisms and endotoxins.
In one study, Dungan and his colleagues set up three sampling sites at a 10,000-cow, open-freestall dairy to measure airborne endotoxins and culturable microorganisms like bacteria and fungi during fall, spring and summer.
ARS said the researchers found that overall average inhalable airborne endotoxin concentrations were 5 endotoxin units (EU) per cubic meter of air 655 ft. upwind of the barn — their "background" levels" — and 426 and 56 EU per cubic meter of air 165 ft. and 655 ft. downwind of the barn, respectively.
Close to the barn, endotoxin concentrations at night were significantly higher than morning concentrations and similar to afternoon concentrations. The scientists attributed the higher levels to increased animal activity and lower windspeeds during these times, ARS said. However, at the other two sites, endotoxin concentrations did not vary significantly over 24 hours.
Samples of bacterial concentrations showed a similar pattern, with the highest counts — 84,000 colonies per cubic meter of air — measured near the barn, ARS said, and the other two sites had less than 8,000 colonies per cubic meter of air. As with the daily endotoxin concentrations, bacterial concentrations near the barn increased significantly at night, but concentrations farther downwind did not.