Search Results

Abstract

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.

Design—Cross-sectional study.

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 2005;226:589–594)

Abstract

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 6 horses.

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 magnification.

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)

Abstract

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.

Abstract

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.

Design—Cohort study.

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.

Abstract

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.

Abstract

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 (C_t) 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, C_t 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 2005;66:915–920)

Abstract

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 Michigan.

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 Res 2005;66:1285–1291)

Abstract

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.

Abstract

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.

Design—Cross-sectional study.

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.