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Prevalence of Salmonella spp on conventional and organic dairy farms

Charles P. Fossler DVM, PhD1,2, Scott J. Wells DVM, PhD, DACVPM3, John B. Kaneene DVM, MPH, PhD4, Pamela L. Ruegg DVM, MPVM5, Lorin D. Warnick DVM, PhD, DACVPM6, Jeffrey B. Bender DVM, MS, DACVPM7, Sandra M. Godden DVM, DVSc8, Lisa W. Halbert DVM9, Amy M. Campbell BS10, and Angela M. Geiger Zwald BS11
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  • 1 Department of Clinical and Population Science, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108
  • | 2 Present address is National Surveillance Unit, Centers for Epidemiology and Animal Health, 2150 Centre Ave, Bldg B, Mail Stop 2E7, Fort Collins, CO 80526.
  • | 3 Department of Clinical and Population Science, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108.
  • | 4 Population Medicine Center, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824.
  • | 5 Department of Dairy Science, College of Agriculture and Life Sciences, University of Wisconsin, Madison, WI 53706.
  • | 6 Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853.
  • | 7 Department of Clinical and Population Science, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108.
  • | 8 Department of Clinical and Population Science, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108.
  • | 9 Population Medicine Center, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824
  • | 10 Population Medicine Center, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824.
  • | 11 Department of Dairy Science, College of Agriculture and Life Sciences, University of Wisconsin, Madison, WI 53706.

Abstract

Objective—To describe the occurrence of fecal shedding, persistence of shedding over time, and serogroup classification of Salmonella spp on a large number of dairy farms of various sizes.

Design—Longitudinal study.

Sample Population—22,417 fecal samples from cattle and 4,570 samples from the farm environment on 110 organic and conventional dairy farms in Minnesota, Wisconsin, Michigan, and New York.

Procedure—5 visits were made to each farm at 2-month intervals from August 2000 to October 2001. Fecal samples from healthy cows, calves, and other targeted cattle groups and samples from bulk tank milk, milk line filters, water, feed sources, and pen floors were collected at each visit. Bacterial culture was performed at 1 laboratory.

ResultsSalmonella spp were isolated from 4.8% of fecal samples and 5.9% of environmental samples; 92.7% of farms had at least 1 Salmonella-positive sample. The 75th percentile for median within-herd prevalence of Salmonella spp in cattle for 5 sampling visits to a given farm was 2.0% and for maximum within-herd prevalence of Salmonella spp was 13.6%. Farms with a median within-herd prevalence of Salmonella spp of ≥ 2.0% accounted for 76.3% of Salmonella-positive samples. There was no significant difference in the prevalence of Salmonella spp between conventional and organic farms. Seasonal differences in Salmonella shedding were observed. More farms had at least 1 serogroup B isolate than any other serogroup, whereas serogroup E1 was the most common among all Salmonella-positive samples. More than 1 serogroup was isolated on 76.4% of Salmonella-positive farms.

Conclusions and Clinical RelevanceSalmonella spp were isolated from > 90% of dairy farms; however, 25% of farms accounted for > 75% of Salmonella-positive samples. This information is critical for the direction of intervention strategies to decrease the prevalence of Salmonella spp on dairy farms. (J Am Vet Med Assoc 2004;225:567–573)

Abstract

Objective—To describe the occurrence of fecal shedding, persistence of shedding over time, and serogroup classification of Salmonella spp on a large number of dairy farms of various sizes.

Design—Longitudinal study.

Sample Population—22,417 fecal samples from cattle and 4,570 samples from the farm environment on 110 organic and conventional dairy farms in Minnesota, Wisconsin, Michigan, and New York.

Procedure—5 visits were made to each farm at 2-month intervals from August 2000 to October 2001. Fecal samples from healthy cows, calves, and other targeted cattle groups and samples from bulk tank milk, milk line filters, water, feed sources, and pen floors were collected at each visit. Bacterial culture was performed at 1 laboratory.

ResultsSalmonella spp were isolated from 4.8% of fecal samples and 5.9% of environmental samples; 92.7% of farms had at least 1 Salmonella-positive sample. The 75th percentile for median within-herd prevalence of Salmonella spp in cattle for 5 sampling visits to a given farm was 2.0% and for maximum within-herd prevalence of Salmonella spp was 13.6%. Farms with a median within-herd prevalence of Salmonella spp of ≥ 2.0% accounted for 76.3% of Salmonella-positive samples. There was no significant difference in the prevalence of Salmonella spp between conventional and organic farms. Seasonal differences in Salmonella shedding were observed. More farms had at least 1 serogroup B isolate than any other serogroup, whereas serogroup E1 was the most common among all Salmonella-positive samples. More than 1 serogroup was isolated on 76.4% of Salmonella-positive farms.

Conclusions and Clinical RelevanceSalmonella spp were isolated from > 90% of dairy farms; however, 25% of farms accounted for > 75% of Salmonella-positive samples. This information is critical for the direction of intervention strategies to decrease the prevalence of Salmonella spp on dairy farms. (J Am Vet Med Assoc 2004;225:567–573)