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Reliability of environmental sampling to quantify Mycobacterium avium subspecies paratuberculosis on California free-stall dairies

S. S. Aly^*,1, R. J. Anderson, R. H. Whitlock, T. L. Fyock, S. McAdams, J. M. Adaska, J. Jiang^# and I. A. Gardner^*

^* Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis 95616
California Department of Food and Agriculture, Animal Health Branch, Sacramento 95814
Johne’s Research Laboratory, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, 382 West Street Road, Kennett Square 19348
California Animal Health and Food Safety Laboratory, Tulare Branch, 18830 Road 112, Tulare 93274
^# Department of Statistics, University of California, Davis 95616

¹ Corresponding author: saly{at}ucdavis.edu

The reliability of environmental sampling to quantify Mycobacterium avium ssp. paratuberculosis (MAP) based on collector and time was evaluated. Fecal slurry samples were collected using a standardized protocol simultaneously by 2 collectors of different experience levels. Samples were collected from 30 cow pens on 4 dairies every other day on 3 occasions while cow movements between pens were minimal. The 4 study herds had moderate MAP seroprevalence and were housed in free-stall dairies in central California. Results of testing the environmental samples for MAP using PCR and culture were strongly correlated. The reliability of environmental sampling simultaneously by different collectors as estimated by the intraclass correlation coefficient was excellent (81%) for PCR and good (67%) for culture and may justify comparison of quantitative results of samples collected by different investigators. The reliability of environmental sampling over a 5-d period was good (67 and 64% for PCR and culture results, respectively), which justifies the utility of environmental sampling to identify pens with a high MAP bioburden between routine cow pen changes on a dairy. Environmental sampling of free-stall pens using the standardized sampling protocol yielded comparable PCR and culture results across collectors with different experience levels and at different times within a 5-d period.

Key Words: reliability • environmental sampling • Mycobacterium avium ssp. paratuberculosis • quantitative real-time PCR