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, according to US Department of Agriculture research.
In the western US, dairy cows are kept in outdoor pens or in a combination of exercise pens and barns at open-freestall facilities. According to the USDA, residents in nearby communities want to know if their proximity to these facilities increases the potential risk of exposure to airborne microorganisms and endotoxins.
A recent study by the USDA’s Agricultural Research Service 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.
According to the study, overall average inhalable airborne endotoxin concentrations were 5 endotoxin units per cubic meter of air 655 feet upwind of the barn — their “background” levels” — and 426 and 56 EU per cubic meter of air 165 and 655 feet 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 attribute the higher levels to increased animal activity and lower windspeeds during these times. But at the other two sites, endotoxin concentrations did not vary significantly over 24 hours, the study shows.
Samples of bacterial concentrations showed a similar pattern, with the highest counts — 84,000 colonies per cubic meter of air — measured near the barn. 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, the study shows.
Methane emissions generated by manure and ruminants such as cattle and sheep as well as those produced by fossil fuel extraction and refining are much higher than estimates reported by the EPA, according to a study published in the Proceedings of the National Academy of Sciences in November.
Methane emissions produced by agriculture could be twice as high as EPA estimates, according to the Anthropogenic Emissions of Methane in the United States study. The discrepancy in methane source estimates is particularly pronounced in the south-central United States, where researchers found total emissions 2.7 times greater than other estimates.