Objective—To compare antimicrobial susceptibility
patterns of Escherichia coli isolates cultured from
fecal samples from cows and calves on dairy farms
that used organic (ie, no or severely limited antimicrobial
use) versus conventional production methods.
Sample Population—Fecal samples from 10 cows
and 10 calves on each of 30 organic dairy farms and
30 neighboring conventional dairy farms in Wisconsin.
Procedure—E coli isolates obtained from the fecal
samples were tested for susceptibility to 17 antimicrobials
by means of a microbroth dilution test.
Prevalence of antimicrobial resistance was compared
between organic and conventional dairy farms.
Results—E coli was isolated from 1,121 (94%) fecal
samples. Farm type (organic vs conventional) and animal
age (cow vs calf) were significantly associated with
odds that E coli isolates would be resistant to various
antimicrobials. After controlling for age, logistic regression
analyses indicated that isolates from conventional
dairy farms had significantly higher rates of resistance
to ampicillin, streptomycin, kanamycin, gentamicin,
chloramphenicol, tetracycline, and sulfamethoxazole
than did isolates from organic dairy farms. However, no
significant differences were detected for the 10 other
antimicrobials that were tested.
Conclusions and Clinical Relevance—Results indicated
that compared with isolates from conventional dairy
farms, E colii solates from organic dairy herds have significantly
lower prevalences of resistance to 7 antimicrobials;
however, prevalence of resistance was not significantly
different for 10 other antimicrobials. Resistance
was more common for isolates from calves than for isolates
from adult dairy cows. (J Am Vet Med Assoc
Objective—To describe the vascular anatomy of the
palmar digital artery and its major branches in the
equine foot and to quantify the diameter of these vessels
by use of digital angiograms.
Sample Population—6 thoracic limbs obtained from
Procedure—Distal portions of each limb were perfused
with aerated Krebs-Henseleit solution. Digital
angiograms were acquired in standing and lateral
recumbent positions, following an intra-arterial injection
of iopamidol. Select vessels were measured on
radiographic views, and values were corrected for
Results—The palmar digital artery tapered from
2.28 mm at the coronary region to 1.61 mm at the
entrance to the solar canal, and the major arterial
branches ranged in diameter from 0.71 to 1.42 mm in
the standing position.
Conclusions and Clinical Relevance—Digital
angiography is useful for imaging small vessels, but
penumbra limits the image resolution of the
macrovasculature of the foot. The palmarodorsal projection
is more useful for evaluation of the terminal
arch and solar branches, but 2 projections are necessary
for a thorough examination of the foot. Image
magnification, position of horse, and vascular
response to contrast medium must be considered in
the quantitative assessment of vessel diameter.
Digital angiography may be performed in clinical
cases and research models for examination of vascular
perfusion of the distal portion of the limb. (Am J
Vet Res 2000;61:255–259)
Objective—To determine the effect of bovine leukemia virus (BLV) infection on absolute neutrophil and lymphocyte concentrations in healthy lactating Holstein dairy cattle.
Design—Observational cross-sectional survey.
Animals—311 healthy lactating Holstein dairy cattle from herds in Michigan (n = 2), Wisconsin (1), Iowa (1), and Pennsylvania (1).
Procedures—Whole and anticoagulated (EDTA) blood samples were collected. Serum samples were tested for antibody against BLV by use of an ELISA. Absolute neutrophil and lymphocyte concentrations were measured in EDTA blood samples with an automated hematology analyzer and manual differential cell counts.
Results—208 cows tested positive and 103 cows tested negative for anti-BLV antibodies. Neutrophil concentration was not significantly different between BLV-positive versus BLV-negative cattle. The distribution of lymphocyte concentration was positively skewed for the entire cow population (n = 311) and the BLV-positive subset (208). In contrast, lymphocyte concentration distribution was approximately normal for BLV-negative cows (n = 103). Consequently, the presence or absence of BLV infection strongly influenced the calculated neutrophil-to-lymphocyte concentration ratio.
Conclusions and Clinical Relevance—Results indicated that absolute lymphocyte concentration is significantly affected by BLV infection in dairy cattle. Accordingly, hematologic reference intervals should be derived from healthy animals that are not infected with BLV and patient BLV status must be considered for meaningful interpretation of lymphocyte concentration. We recommend that the calculated neutrophil-to-lymphocyte ratio be abandoned because it does not provide more information than direct comparison of patient absolute leukocyte concentration with updated reference intervals from healthy BLV-negative cattle.
Objective—To determine factors that influenced culling or death of cows with left displaced abomasum (LDA) subsequent to correction by a roll-and-toggle (R&T) procedure or via laparotomy.
Animals—810 Holstein dairy cows with LDA.
Procedures—Data regarding method of repair and risk factors for survival after correction of LDA were collected during a 1-year period. Outcomes were compared at days 14 and 60 after LDA correction for 3 groups of cattle (veterinarians performed R&T [V-R&T], herd personnel performed R&T [H-R&T], and veterinarians performed surgical repair via laparotomy [V-Surg]).
Results—Survival rates 14 days after LDA correction for the V-R&T, H-R&T, and V-Surg groups were 87% (286/329), 81% (327/403), and 85% (66/78), respectively. At 60 days after LDA correction, survival rates for the V-R&T, H-R&T, and V-Surg groups were 79% (260/329), 71% (286/403), and 73% (57/78), respectively. Multivariable analysis indicated that factors positively associated with failure to remain in the herd at 60 days after LDA correction included current mastitis status, history of a previous LDA, high preoperative risk, and correction of LDA by herd personnel rather than by a veterinarian.
Conclusions and Clinical Relevance—Correction of LDA by veterinarians via an R&T procedure yielded results that were generally comparable to those for correction by veterinarians via laparotomy. Although survival rates at days 14 and 60 after surgery differed significantly between the V-R&T and H-R&T groups, herd personnel in this study used the R&T procedure to correct LDA and achieved survival rates within the range for those of practicing veterinarians.
Objective—To determine the effect of hyperimmunization with an Escherichia coli J5 bacterin on serum IgG2 concentration, incidence of clinical mastitis, and rate of survival to the end of the lactation period (ie, day 305) in adult lactating dairy cattle.
Design—Randomized controlled trial.
Animals—1,012 Holstein cows in their second lactation and greater.
Procedures—All cows were given 3 doses of the J5 bacterin; cows in the hyperimmunization group were given an additional 3 doses during the first 3 months of lactation. Blood was collected from a small sample of cows to determine anti-J5 IgG2 concentrations.
Results—Cows in the hyperimmunization group had higher mean serum anti-J5 IgG2 concentrations than did control cows 28 days after administration of the fourth, fifth, and sixth doses of the J5 bacterin. However, mean serum anti-J5 concentrations during the subsequent lactation were not significantly different between groups. The proportions of cows that developed clinical mastitis were not significantly different between groups. However, control cows were more likely to have severe clinical mastitis than were cows in the hyperimmunization group. The percentage of control cows that remained in the herd to day 305 was significantly lower than the percentage of cows in the hyperimmunization group that did.
Conclusions and Clinical Relevance—Results suggested that hyperimmunization of mature lactating dairy cattle was associated with increased serum anti-J5 IgG2 concentrations and decreased incidence of severe clinical mastitis, but did not alter survival rate of cows that developed severe clinical mastitis.
Objective—To compare 5 methods of preparation of
RNA from feline urine samples for use in a feline calicivirus
(FCV), p30 gene-based, real-time reverse-transcriptase
polymerase chain reaction (RT-PCR) assay.
Sample Population—Urine and blood samples from
6 specific-pathogen-free cats.
Procedures—Aliquots of each urine sample (unmodified,
centrifuged, or mixed with whole or hemolyzed
blood) were spiked with FCV and serially diluted in
urine. Serial dilutions of FCV in tissue culture medium
were used as positive controls. Viral RNA was prepared
via dilution and thermal inactivation (DT
method), polyethylene glycol precipitation (PEG
method), isolation with oligo(dT)25-coated magnetic
beads (dTMB method), or extraction by use of 2 silica
gel–based columns (RN or QA method). Lower detection
limits and mean RT-PCR threshold cycle (Ct) values
associated with each RNA preparation method
and sample type were compared.
Results—Because DT-prepared samples yielded negative
results via RT-PCR assay, this method was not evaluated.
Lower detection limits (TCID50/sample) for the
assay in urine were 1,950, 104, 11, and 7 for PEG-,
dTMB-, RN-, and QA-prepared samples, respectively. For
RN and QA preparations, Ct values were similar and significantly
lower than those for dTMB and PEG preparations.
Overall, urine modifications did not affect FCV RNA
detection in dTMB-, QA-, and RN-prepared samples.
Conclusions and Clinical Relevance—Of the methods
evaluated, the RN and QA methods of RNA
preparation were most appropriate for the FCV RTPCR
assay. An RT-PCR assay optimized for detection
of FCV in feline urine may aid investigations of FCVinduced
urinary tract diseases in cats. (Am J Vet Res
Objective—To estimate herd-level sensitivity (HSe),
specificity (HSp), and predictive values for a positive
(HPVP) and negative (HPVN) test result for several
testing scenarios for detection of tuberculosis in cattle
by use of simulation modeling.
Sample Population—Empirical distributions of all
herds (15,468) and herds in a 10-county area (1,016) in
Procedures—5 test scenarios were simulated: scenario
1, serial interpretation of the caudal fold tuberculin
(CFT) test and comparative cervical test (CCT);
scenario 2, serial interpretation of the CFT test and
CCT, microbial culture for mycobacteria, and polymerase
chain reaction assay; scenario 3, same as scenario
2 but specificity was fixed at 1.0; and scenario 4,
sensitivity was 0.9 (scenario 4a) or 0.95 (scenario 4b),
and specificity was fixed at 1.0.
Results—Estimates for HSe were reasonably high,
ranging between 0.712 and 0.840. Estimates for HSp
were low when specificity was not fixed at 1.0.
Estimates of HPVP were low for scenarios 1 and 2
(0.042 and 0.143, respectively) but increased to 1.0
when specificity was fixed at 1.0. The HPVN remained
high for all 5 scenarios, ranging between 0.995 and
0.997. As herd size increased, HSe increased and HSp
and HPVP decreased. However, fixing specificity at
1.0 had only minor effects on HSp and HPVN, but HSe
was low when the herd size was small.
Conclusions and Clinical Relevance—Tests used
for detecting cattle herds infected with tuberculosis
work well on a herd basis. Herds with < approximately
100 cattle should be tested more frequently or for
a longer duration than larger herds to ensure that
these small herds are free of tuberculosis. (Am J Vet
Objective—To determine effects of injection site on antibody response to J5 Escherichia coli bacterin.
Animals—28 adult Holstein cows.
Procedures—Cows were randomly assigned as control cattle (n=4cows), not administered J5 E coli bacterin; 3X (8), administered 3 doses of bacterin SC in the left side of the neck; 5XN (8), administered 5 doses of bacterin SC in the left side of the neck; or 5XSR (8), administered 5 doses of bacterin SC sequentially in the left side of the neck, right side of the neck, right side of the thorax, left side of the thorax, and left side of the neck. Blood samples were collected from the cows to determine anti-J5 E coli IgG1 and IgG2 concentrations.
Results—Vaccinated cows had higher mean serum anti-J5 E coli IgG1 concentrations than did control cows. The 5XN and 5XSR cows had higher mean serum anti-J5 E coli IgG1 concentrations than did 3X cows. Additionally, 5XSR cows had higher mean serum anti-J5 E coli IgG1 concentrations than did 5XN cows. Vaccinated cows had higher mean serum anti-J5 E coli IgG2 concentrations than did control cows. The 5XN and 5XSR cows had higher mean serum anti-J5 E coli IgG2 concentrations than did 3X cows. The 5XSR cows had higher mean serum anti-J5 E coli IgG2 concentrations than did all other groups at 84 days after the fifth vaccination.
Conclusions and Clinical Relevance—Sequential doses of core-antigen bacterins administered at different anatomic locations may improve antibody response in dairy cattle.
Objective—To determine and compare levels and patterns of antimicrobial resistance among Escherichia coli isolated from pigs on farms that did not use antimicrobial agents versus pigs produced under conventional methods.
Sample Population—35 antimicrobial-free and 60 conventional swine farms.
Procedures—Farms were visited once, and fecal samples were collected from 15 finisher pigs if available. One E coli isolate from each sample was tested for susceptibility pattern to 14 antimicrobial agents by use of microbroth dilution.
Results—E coli isolates were recovered from 1,381 (97.1%) of 1,422 fecal samples. Herd size was significantly larger for conventional swine farms. Resistance to ceftriaxone, ciprofloxacin, or nalidixic acid was not observed on any of the 95 farms. Three isolates from 2 conventional farms were resistant to ceftiofur. Conventional farms had significantly higher levels of resistance to ampicillin, sulfamethoxazole, tetracycline, and chloramphenicol, compared with antimicrobial-free farms. Fourteen percent of E coli isolates were susceptible or had intermediate resistance to all the tested antimicrobial agents. The 3 most frequent patterns of multiple resistance were streptomycin-tetracycline, sulfamethoxazole-tetracycline, and kanamycin-streptomycin-sulfamethoxazole-tetracycline.
Conclusions and Clinical Relevance—Cessation of antimicrobial use did not appear to result in an immediate reduction in antimicrobial resistance in swine farms. Prospective studies of long-term antimicrobial usage and cessation are needed to estimate the extent to which food animal production may be contributing to antimicrobial drug resistance and might provide a direct measure of the rates of reversibility of antimicrobial drug resistance that might be achieved by curtailing antimicrobial usage.