Prevalence of Salmonella spp on conventional and organic dairy farms.
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.


METHODS
Longitudinal study.


METHODS
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 NewYork.


METHODS
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.


RESULTS
Salmonella 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 > or = 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
Salmonella 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.
Fossler
Charles P
CP
Department of Clinical and Population Science, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108, USA.
Wells
Scott J
SJ
Kaneene
John B
JB
Ruegg
Pamela L
PL
Warnick
Lorin D
LD
Bender
Jeffrey B
JB
Godden
Sandra M
SM
Halbert
Lisa W
LW
Campbell
Amy M
AM
Zwald
Angela M Geiger
AM
D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology* / Q000382:microbiology; D003612:Dairying / Q000379:methods*; D004783:Environmental Microbiology; D005243:Feces / Q000382:microbiology*; D005260:Female; D008137:Longitudinal Studies; D008824:Michigan / Q000453:epidemiology; D008910:Minnesota / Q000453:epidemiology; D009518:New York / Q000453:epidemiology; D015995:Prevalence; D012475:Salmonella / Q000145:classification* / Q000302:isolation & purification; D012481:Salmonella Infections, Animal / Q000453:epidemiology* / Q000382:microbiology; D012621:Seasons; D012703:Serotyping / Q000662:veterinary; D014922:Wisconsin / Q000453:epidemiology