2016 Incidence rate of pathogen-specific clinical mastitis on conventional and organic Canadian dairy farms

J Dairy Sci. 2016 Feb;99(2):1341-1350. doi: 10.3168/jds.2015-9809. Epub 2015 Dec 10. Levison LJ1, Miller-Cushon EK2, Tucker AL1, Bergeron R3, Leslie KE4, Barkema HW5, DeVries TJ6. Author information 1 Department of Animal Biosciences, University of Guelph, Guelph, ON, N1G 2W1, Canada. 2 Department of Animal Sciences, University of Florida, Gainesville 32611. 3 Department of Animal Biosciences, University of Guelph, Alfred, ON, K0B 1A0, Canada. 4 Department of Population Medicine, University of Guelph, Guelph, ON, N1G 2W1, Canada. 5 Department of Production Animal Health, Faculty of Veterinary Medicine, University of Calgary, Calgary, Alberta T2N 4N1, Canada. 6 Department of Animal Biosciences, University of Guelph, Guelph, ON, N1G 2W1, Canada. Electronic address: tdevries@uoguelph.ca. Abstract Mastitis is a common and costly production disease on dairy farms. In Canada, the incidence rate of clinical mastitis (IRCM) has been determined for conventionally managed dairy farms; however, no studies to date have assessed rates in organically managed systems. The objectives of this observational study were (1) to determine the producer-reported IRCM and predominant pathogen types on conventional and organic dairy farms in Southern Ontario, Canada, and (2) to evaluate the association of both mean overall IRCM and pathogen-specific IRCM with management system, housing type, and pasture access. Data from 59 dairy farms in Southern Ontario, Canada, distributed across conventional (n=41) and organic management (n=18) systems, were collected from April 2011 to May 2012. In addition to management system, farms were categorized by housing method (loose or tie-stall) and pasture access for lactating cows. Participating producers identified and collected samples from 936 cases of clinical mastitis. The most frequently isolated mastitis pathogens were coagulase-negative staphylococci, Bacillus spp., Streptococcus spp., Staphylococcus aureus, and Escherichia coli. The IRCM was higher on conventional farms than organic (23.7 vs. 13.2 cases per 100 cow-years) and was not associated with housing type (loose or tie-stall), pasture access, or herd-average milk yield. Bulk tank somatic cell count tended to be lower on conventional farms than organic (222,000 vs. 272,000 cells/mL). Pathogen-specific IRCM attributed to Staph. aureus, Bacillus spp., and E. coli was greater on conventional than organic farms, but was not associated with housing or any other factors. In conclusion, organic management was associated with reduced overall and pathogen-specific IRCM. KEYWORDS: clinical mastitis; dairy cow; organic; pathogens PMID: 26686728 DOI: 10.3168/jds.2015-9809