Effects of Location for Collection of Air Samples on a Farm and Time of Day of Sample Collection on Airborne Concentrations of Virulent Rhodococcus equi at Two Horse Breeding Farms


Objective: To determine whether airborne concentrations of virulent R equi varied by housing location, time of day, and month (February through July) at 2 horse breeding farms.

Sample Population: 2 farms with recurrent R equi foal pneumonia in central Kentucky.

Procedures: From February through July 2008, air samples were collected hourly for a 24-hour period each month from stalls and paddocks used to house mares with foals. Virulent concentrations of airborne R equi were determined using a colony immunoblot technique and differences were compared using zero-inflated negative binomial methods to determine effects of location, time, and month.

Results: The presence of mares and foals at the sampling site significantly (P = 0.017) modified the effect of location (stall versus paddock) by increasing airborne concentrations of virulent R equi. Relative to the period from midnight through 5:59 AM, airborne concentrations of virulent R equi were significantly (P = 0.016) higher between 6:00 PM through 11:59 PM midnight. There were no significant differences in airborne concentrations between farms or among months.

Conclusions: Airborne concentrations of virulent R. equi were significantly increased by sampling when horses were predominately housed in the sampling site area (ie, higher in stalls when horses were predominately stalled, and higher in paddocks when horses were predominately in paddocks). For ecological and epidemiological studies, there appears to be no difference in airborne concentrations of virulent R. equi among air samples collected between the hours of 6:00 AM and midnight.

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Notes/Citation Information

Published in American Journal of Veterinary Research, v. 72, no. 1, p. 73-79.

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Funding Information

Funded by the Grayson-Jockey Club Research Foundation; additional support was provided by the Link Equine Research Endowment, Texas A&M University. Dr. Wang was partially supported by a grant from the National Cancer Institute (CA74552).