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.
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.
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
≥ 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 Relevance—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. (J Am Vet Med Assoc 2004;225:567–573)
Objective—To describe antimicrobial susceptibility patterns in Campylobacter spp isolated from dairy cattle and farms managed organically and conventionally in the midwestern and northeastern United States.
Sample Population—128 farms.
Procedure—Samples and data were collected every 2 months from August 2000 to October 2001. Fecal samples were collected from calves and cows. Milk samples were obtained from the bulk tank and milk line filters. Environmental samples were obtained from a water source, feed bunks of lactating cows, and cattle housing areas. Campylobacter identification and antimicrobial susceptibility testing were performed at a central laboratory by use of microbroth dilution with 2 customized antimicrobial susceptibility panels.
Results—460 and 1,570 Campylobacter isolates were obtained from organic and conventional dairy farms, respectively. Most isolates from both farm types were susceptible to most antimicrobial agents tested, and antimicrobial susceptibility of conventional dairy isolates was decreased, compared with organic dairy isolates. Low proportions of isolates resistant to ampicillin (< 10%) and moderate proportions resistant (30% to 60%) to kanamycin, sulfamethoxazole, and tetracycline were observed on both farm types. The proportion of isolates resistant to tetracycline was higher for conventional than organic farms.
Conclusions and Clinical Relevance—Campylobacter isolates from dairy cattle and farms managed organically and conventionally had similar patterns of antimicrobial resistance; the proportion of resistant isolates was higher for conventional than organic farms.