Submitted to: American Journal of Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2003
Publication Date: 1/1/2004
Citation: Purdy, C.W., Straus, D.C., Parker, D.B., Wilson, S.C., Clark, R.N. 2004. Comparison of microorganisms and concentration of endotoxin in the air of southern high plains feedyards. American Journal of Veterinary Research. 65:45-52.
Interpretive Summary: The microbial environmental impact of concentrated animal feeding operations (CAFO) on aerosols in and around feedyards is unknown. We compared the aerosol concentrations of microbial organisms (bacterial and fungal) and endotoxins of seven feedyards in the winter and summer. Endotoxins are derived from cell wall parts of Gram-negative staining fecal bacteria which may cause inflammation of the respiratory tract when inhaled. The average endotoxin concentrations of the seven feedyards were significantly higher (8.37 nanograms/cubic meter of air) in the winter than in the summer (2.63 nanograms/cubic meter of air). Seventeen genera of fungi were identified and the aerosol concentration (load) of the fungi and bacteria were established for seven feedyards in the winter and summer. Most bacterial aerosol concentrations were significantly higher in the summer than in the winter. Seven feedyards had significant differences in bacterial and fungal concentrations between them. This may imply that different management systems and many other factors such as number of animals, size of feedyard, and land topography may cause differences in aerosol concentrations. Gram-positive Enterococcus spp coming from manure were frequently found in aerosols of the seven feedyards. No Gram-negative bacteria coming from the manure were cultured from the air. This implies that there is little chance of Gram-negative pathogens (Salmonella spp and Escherichia coli O157:H7) infecting animals or humans from feedyard aerosols. These results are important to feedyard managers, veterinarians, and scientists.
Technical Abstract: The objectives were to determine the bacterial, fungal, and endotoxin concentrations in ambient air in the winter and summer of seven feedyards located in the Southern High Plains of Texas and to identify aerosolized feedyard microbial pathogens which might impact the health of animals and humans. Aerosol microbial samples were collected upwind, on-site, and downwind from each feedyard at 1 m above the ground with Andersen biological 6-stage and 2-stage cascade impactors drawing 28.4 L of ambient air/min for 5 min or 15 min depending on the type of medium used. The resulting microbial colony forming units (CFU) were reported in CFU/m3 of air. Endotoxin samples were collected for 30 min upwind and downwind into the 1st and 6th stage Petri plates of the Andersen impactors, each plate contained 20 ml of water. The mean overall endotoxin concentration were significantly higher (8.37 nanograms/cubic meter of air) in the winter than in the summer (2.63 nanograms/cubic meter of air).There were significantly more microbes on-site and downwind than upwind and more in the summer than in the winter. Among the 7 feedyards there were significantly more aerosolized mean mesophilic bacteria (1441 [195 SE] CFU/m3) than mean anaerobic bacteria (751  CFU/m3) or mean thermophilic bacteria (54  CFU/m3). Feedyard aerosols contained significantly more mean mesophilic fungi (78  CFU/m3) than thermophilic fungi (2 [0.2] CFU/m3). Seventeen genera of fungi were identified and the aerosol concentration of the fungi and bacteria were established for seven feedyards in the winter and summer.There were significant differences among the seven feedyards in microbial concentrations of the air. No Gram-negative enteric pathogens or non-pathogens were found in the feedyard ambient air in the winter or summer. Therefore, it appears that Gram-negative enteric pathogens offer little risk in translocation to remote calves or people by feedyard aerosols.