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J. Dairy Sci. 2009. 92:4229-4238. doi:10.3168/jds.2008-1494
© 2009 American Dairy Science Association ®
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The role of animal movement, including off-farm rearing of heifers, in the interherd transmission of multidrug-resistant Salmonella

B. Adhikari*, T. E. Besser{dagger}, J. M. Gay*, L. K. Fox*, M. A. Davis{dagger}, R. N. Cobbold{ddagger}, A. C. B. Berge* and D. D. Hancock*,1

* AAHP, Field Disease Investigation Unit, Department of Veterinary Clinical Sciences, Washington State University, Pullman 99164
{dagger} Department of Veterinary Microbiology and Pathology, Washington State University, Pullman 99164
{ddagger} School of Veterinary Science, The University of Queensland, Brisbane, Queensland 4072, Australia

1 Corresponding author: hancock{at}wsu.edu

Fifty-nine commercial dairy farms were sampled 7 times over 15 to 21 mo to determine the role of animal movement, including off-farm rearing of heifers, in the interherd transmission of multidrug-resistant (MDR) Salmonella spp. Farm management data were collected by on-site inspections and questionnaires on herd management practices before and after the study. Forty-four percent (26/59) of herds did not acquire any new MDR Salmonella strains. The number of newly introduced MDR Salmonella strains acquired by the remaining 56% (33/59) of herds ranged from 1 to 8. Logistic regression models indicated that off-farm heifer raising, including contract heifer raising where heifers commingle with cattle from other farms [commingled heifers, odds ratio (OR) = 8.9, 95% confidence interval (CI): 2.4, 32.80], and herd size per 100-animal increment (herd size, OR = 1.04, 95% CI, 1.01, 1.05) were significantly associated with the introduction of new MDR Salmonella strains. The negative binomial regression similarly revealed that commingled heifers [relative risk (RR) = 2.3, 95% CI: 1.1, 4.7], herd size per 100 animals (RR = 1.02, 95% CI, 1.01, 1.03), and a history of clinical salmonellosis diagnosed before the study (RR = 2.5, 95% CI, 1.3, 5.0) were significantly associated with the number of new MDR Salmonella strains that were introduced. Factors not associated with the introduction of new MDR Salmonella strains were housing of heifers and cows in the same close-up pen, a common hospital-maternity pen, and the number of purchased cattle. This study highlights the role of animal movement in the interherd transmission of MDR Salmonella spp.

Key Words: multidrug-resistant Salmonella • dairy farm • herd-level risk factor


Related articles in JDS:

Introduction of new multidrug-resistant Salmonella enterica strains into commercial dairy herds
B. Adhikari, T. E. Besser, J. M. Gay, L. K. Fox, M. A. Davis, R. N. Cobbold, A. C. Berge, R. McClanahan, and D. D. Hancock
JDS 2009 92: 4218-4228. [Abstract] [Full Text]  





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