Relative and Qualitative Aspects of Aerial Bacteria and Dust in Swine Houses

Aerial levels of bacterial-colony-forming particles (BCFP) in lung-depositable size ranges were determined using an eight-stage Andersen viable sampler with tryptose agar. Aerial levels of BCFP≤4.7 µm and ≤3.3 µm in aerodynamic diameter were significantly and positively correlated with total-aerial-BCFP level in swine-house air. On average, 31% of aerial BCFP were ≤4.7 µm and 15% were ≤3.3 µm in four University enclosed swine houses (n = 192); 30% and 22%, respectively, in a University modified-open-front house (n = 44) and 28% and 11%, respectively, in 12 houses at five commercial operations (n = 24). Aerial-dust level was determined using a Staplex high-volume sampler. Aerial-BCFP and -dust levels were significantly and positively correlated. There tended to be fewer aerial BCFP per unit of aerial dust in the modified-open-front house than in the enclosed houses at the University. Ten swine houses at commercial operations and four at the University were studied a total of 16 times to determine concentrations and sizes of aerial bacterial particles which formed colonies on tryptose (general medium), Chapman-Stone (special medium for staphylococci), KF Streptococcus (fecal streptococci) and MacConkey (coliforms) agars, respectively. Ratio of bacterial-colony-forming-particle (BCFP) count on Chapman-Stone agar to that on tryptose averaged .36, that on KF Streptococcus to that on tryptose averaged .13 and that on Mac-Conkey to that on tryptose averaged less than .01. Twenty-one percent of the staphylococcal BCFP and streptococcal BCFP, respectively, and 9% of the coliform BCFP, were lung-depositable (≤4.7 µm in diameter). Nitrogen content of aerial dust in a swine-finishing house, in which a 13% crude-protein (CP) diet was fed, averaged 4.6%, or (4.6 × 6.25) = 28.7% CP (n = 17). Settled dust in a farrowing house, in which a 12% CP diet was used, averaged 23.3% CP (n = 6), whereas that in a room in which diets having 12 to 16% CP were prepared averaged 13.0% CP (n = 4). It was concluded that much of the dust in swine-house air was feed dust.