title: Sensitivity of solid culture, broth culture, and real-time PCR assays for milk and colostrum samples from Mycobacterium avium ssp. paratuberculosis-infectious dairy cows.
abstract: Mycobacterium avium ssp. paratuberculosis (MAP) can be shed in feces, milk, and colostrum. The goal of this study was to assess assays that detect MAP in these sample types, including effects of lactation stage or season. Understanding the performance of these assays could improve how they are used, limiting the risk of infection to calves. Forty-six previously confirmed MAP-positive cows from 7 Atlantic Canadian dairy farms were identified for colostrum sampling and monthly sampling of milk and feces over a 12-mo period. Samples were assayed for MAP using solid culture, broth culture, and direct real-time PCR (qPCR). Across assay types, test sensitivity when applied to milk samples averaged 25% of that when applied to fecal samples. For colostrum samples, sensitivity depended on assay type, with sensitivity of qPCR being approximately 46% of that in feces. Across sample types, sensitivity of qPCR was higher than that of the other assays. Sensitivity of qPCR, when applied to milk samples, was significantly higher in summer than in other seasons. Summer was also the season with highest agreement between milk and fecal samples collected within the same month. Our results suggest that qPCR would detect more cows shedding MAP in their milk and colostrum than solid or broth culture assays, particularly during the summer, thus providing better management information to limit exposure of calves to this infectious organism.
authors.affiliation: Department of Health Management, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, Prince Edward Island C1A 4P3, Canada. Electronic address: elaurin@upei.ca.
authors.forename: Emilie
authors.initials: E
authors.lastname: Laurin
authors.affiliation: Department of Health Management, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, Prince Edward Island C1A 4P3, Canada.
authors.forename: Shawn
authors.initials: S
authors.lastname: McKenna
authors.affiliation: Department of Health Management, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, Prince Edward Island C1A 4P3, Canada.
authors.forename: Marcelo
authors.initials: M
authors.lastname: Chaffer
authors.affiliation: Department of Health Management, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, Prince Edward Island C1A 4P3, Canada.
authors.forename: Greg
authors.initials: G
authors.lastname: Keefe
mesh_terms: D000818:Animals; D002170:Canada; D002417:Cattle; D002418:Cattle Diseases / Q000175:diagnosis / Q000382:microbiology*; D003126:Colostrum / Q000382:microbiology*; D005243:Feces / Q000382:microbiology; D005260:Female; D007774:Lactation; D008892:Milk / Q000382:microbiology*; D016927:Mycobacterium avium subsp. paratuberculosis / Q000302:isolation & purification*; D010283:Paratuberculosis / Q000175:diagnosis / Q000382:microbiology*; D060888:Real-Time Polymerase Chain Reaction / Q000662:veterinary*; D012621:Seasons; D012680:Sensitivity and Specificity
keywords: Mycobacterium avium subspecies paratuberculosis; milk and colostrum; real-time PCR; season