Airborne microbial flora in a cattle feedlot.

A total of 1,408 cattle held in eight commercial feedlot pens were used to examine the quantity and diversity of microorganisms in cattle feedlot air. The effect of two feeding patterns on the generation of airborne dust and the total numbers of microorganisms was also examined (four feedlot pens/treatment). Microbial samples were collected, and dust particles that were 2.5 microm or less in diameter were measured with a Dustrak monitor during the evening dust peak for 4 days at sites both upwind and downwind of the feedlot pens. An Andersen biological cascade sampler was employed with different medium and incubation combinations for the capture and identification of bacteria and fungi. The results showed that when bacteria were considered, only nonpathogenic gram-positive organisms were recovered. However, gram-negative bacteria may have been present in a viable but nonculturable state. Fungi were recovered in smaller numbers than bacteria, and none of the fungi were pathogenic. The Dustrak results showed that one feeding pattern resulted in cattle behavior that generated levels of downwind dust lower (P = 0.04) than the levels generated by the behavior resulting from the other feeding pattern. However, the Andersen sampler results showed that there were no differences between feeding patterns with regard to the total number or diversity of microorganisms. The disparity may have been due to the different operating principles of the two systems. The overall numbers of microorganisms recovered were lower than those reported in studies of intensively housed farm animals in which similar recovery techniques were used.