Airborne Microbial Flora in a Cattle Feedlot

Abstract

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 m 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.High dust production is a feature of many cattle feedlots (20). MacVean et al. (13) found that a broad temperature range and an increase in dust particles in the 2.0-to 3.3-m size range in feedlots were associated with an increased incidence of cattle pneumonia. This was attributed to the dust load stressing the respiratory system and predisposing cattle to infection by bacterial and viral pathogens. The numbers and types of microorganisms that are either bound to feedlot dust or individually airborne may also play a contributing role. However, there have been no previous studies that have examined the microbial composition of cattle feedlot air.Dry, warm conditions and active cattle behavior have been found to be the principal contributors to dust production in cattle feedlots. This production peaks during the evening hours (F. W. Mitlöhner, J. L. Morrow, J. W. Dailey, and J. J. McGlone, unpublished data). This is an active period for cattle, characterized by increased numbers of agonistic interactions and walking and running behaviors (8). A standard feeding practice in some West Texas feedlots is to feed at sunrise, 1000 h, and 1200 h. This protocol results in cattle that have digested their food by the evening, which coincides with the active, dust-generating period. It was hypothesized that feeding cattle at sunrise, noon, and sunset would replace the evening active period with a period of eating and...

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