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in Journal of the American Veterinary Medical Association
in Journal of the American Veterinary Medical Association

Objective

To assess the number of bacteria and presumptive antibiotic residues in milk fed to calves and to identify those bacteria and the antibiotic susceptibility of selected bacterial strains.

Design

Cross-sectional prospective study.

Sample Population

189 samples obtained from 12 local dairies.

Procedure

Samples of waste milk and milk-based fluids (eg, milk replacer, colostrum, bulk-tank milk) were obtained. Cumulative number of viable bacteria was determined. Bacteria were cultured aerobically, and antibiotic susceptibility testing of selected strains was performed. Presumptive antibiotic residues were detected by use of test kits.

Results

Geometric mean of the cumulative number of bacteria for waste milk samples was significantly higher than for other types of milk or milk-based products. Streptococcus sp (84/165 samples) and Enterobacteriaceae (83/165 samples) were the predominant bacteria identified, followed by Staphylococcus sp (68/165 samples). Escherichia coli was the gram-negative species most commonly isolated (52/165 samples; 32%); however, none were strain O157. Salmonella sp or Mycoplasma sp were not isolated. Of 189 samples, 119 (63%) were positive when tested for β-lactams or tetracycline by use of 2 commercially available assays. In vitro, some bacteria were resistant to commonly used antibiotics.

Clinical Implications

Waste milk that has not been effectively treated (eg, pasteurization) to reduce microbial load prior to use as calf feed should be used with caution, because it may contain a high number of bacteria that may be pathogenic to cattle and human beings. Antibiotic residues that would constitute violative amounts and existence of multiple antibiotic resistant bacterial strains are concerns in calf health management and dairy food safety. (J Am Vet Med Assoc 1997;211:1029–1035)

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in Journal of the American Veterinary Medical Association

Abstract

Objective

To determine the seroprevalence of antibodies to gram-negative core antigens (GNCA) in specific-pathogen-free (SPF) rabbits (ie, free of Pasteurella multocida) and rabbits of undefined bacterial status (conventional).

Sample Population

Serum samples were obtained from 7 groups of rabbits. The SPF rabbits comprised 2 adult groups and 1 immature group, whereas the 4 groups of conventional rabits were all adults.

Procedure

A seroprevalence survey was conducted on rabbit sera for antibodies against GNCA, using an Escherichia coli J5 antigen-capture ELISA.

Results

Collective geometric mean titer (GMT) of adult rabbits was 1:6,463. The GMT of each of the 6 groups of adult rabbits was 1:956, 1:1,133, 1:4,525, 1:5,338, 1:7,669, and 1:25,600. Titers of populations differed significantly.

Conclusion

Data analysis revealed there were anti-GNCA antibodies in rabbits. Similar to other species, the prevalence of IgM and IgG anti-GNCA antibodies increased with age. The IgG response was more marked than the IgM response. The SPF rabbits had lower IgG anti-GNCA titers than conventional rabbits, indicating possible cross-reactive epitopes between P multocida and Enterobacteriaceae. Rabbits with the highest anti-GNCA titers were those used in polyclonal antibody production, possibly stemming from endotoxin contamination of antigen or adjuvant.

Clinical Relevance

The possible cross-reactive antibodies directed at homologous wall components of Pasteurellaceae and Enterobacteriaceae could prove to be a possible heterotypic vaccination strategy for the protection of rabbits against pasteurellosis. investigators should determine whether antigen impurity (endotoxin contamination) influences epitope focus during polyclonal antibody production and whether it affects sera variability among rabbits. (Am J Vet Res 1999;60:501-506).

Free access
in American Journal of Veterinary Research

Abstract

Objective

To evaluate the ability of commercially available Escherichia coli J5 bacterin to protect rabbits from experimental challenge with Pasteurella multocida.

Animals

40 P multocida-free New Zealand White rabbits.

Procedures

Rabbits were assigned to 1 of 4 groups of 10 rabbits each. Three of the groups were inoculated SC with J5 bacterin at 8 weeks old. Inoculation was repeated 3 and 6 weeks later. The fourth group was not inoculated and served as controls. Groups 1, 2, and 3 were given 109, 108, and 107 colony forming units (CFU), respectively. Response was monitored by titer assessment, using an E coli J5 antigen capture ELISA. Five weeks after the last inoculation, all rabbits were challenged with P multocida and observed for an additional 5 weeks. Clinical, hematologic, serologic, culture, and necropsy data were collected.

Results

Inoculation of rabbits with 109 CFU of E coli J5 bacterin-induced titers that were significantly greater than titers of rabbits vaccinated with 108 or 107 CFU or those in controls. The incidence of acute bacteremia was lower in rabbits with high titers. At necropsy, prevalence of lesions typical of P multocida was not significantly different among groups. Prevalence of histologic lesions was also not significantly different among groups.

Conclusions and Clinical Relevance

Although the bacterin induced considerable antibody response and possibly reduced the rate of bacteremia, antibodies were not protective against long-term colonization or infection of the frontal sinuses or tympanic bullae by the challenge strain of P multocida. This bacterin in its currently available form is unlikely to aid in reducing the prevalence of pasteurellosis in rabbits. (Am J Vet Res 1999;60:853–859)

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in American Journal of Veterinary Research

Objective

To evaluate alterations in lymphocyte subpopulations, CBC results, and clinical signs in neonatal calves inoculated with 3 commercially available proprietary multiple-antigen vaccines containing known quantities of endotoxin.

Design

Prospective, randomized controlled field trial.

Animals

36 healthy Holstein heifer calves between 3 and 31 days old.

Procedure

Vaccines were administered to 18 calves according to label instructions, except for the recommended age of administration. The 18 other calves served as unvaccinated controls. Two weeks after entry into the study, calves were given secondary doses of the same vaccines. Calves in both groups were examined and blood samples were collected for determination of lymphocyte subpopulations and hematological parameters once daily for 5 days beginning on the day that both the primary and the secondary vaccinations were given. Lymphocyte subpopulations, including BoCD2*, BoCD4+, BoCD8+, B cells, and γ/δ T cells, were determined by use of flow cytometry, using monoclonal antibodies as markers.

Results

Vaccinated calves did not develop clinical signs of illness. There were no significant differences in absolute numbers of lymphocyte subpopulations between vaccinated and unvaccinated calves. Vaccinated calves had significantly higher rectal temperatures, total WBC counts, and absolute neutrophil counts than did control calves. These differences persisted for 3 to 4 days after vaccination.

Clinical Implications

Findings confirm empirical observations that vaccination with multiple products at the same time may induce evidence of an inflammatory response in most calves. Additional research is indicated to further evaluate the safety of using multiple vaccines simultaneously. (J Am Vet Med Assoc 1996;209:638-642)

Free access
in Journal of the American Veterinary Medical Association

Summary

Antimicrobial drug residue testing was performed on milk samples obtained from 8 cows with experimental endotoxin-induced mastitis, using 4 commercially available assay kits. Although none of the cows in the study received antimicrobials, only 1 of the 4 assay procedures, assay C, had consistently negative results (specificity = 1.00). The proportion of positive assay results varied from 0 to 1.00 among combinations of sampling time, sample status (endotoxin-infused quarter vs composite noninfused sample). The proportion of positive results found when assay C was used (0) differed significantly from the proportion found when the 3 other assays were used. The proportion of positive results did not differ significantly between assay A (0.45) and assay B (0.48); however, both assays had a significantly lower proportion of positive assays than did assay D (0.86).

Logistic regression models were developed predicting positive milk antimicrobial drug residue assay results as a function of assay kit, sample status, and time interval following experimental challenge exposure. Using assay A as a baseline risk, assay B and assay D were more likely to have positive assay results, and assay C had a decreased risk of positive assay results. Milk samples from endotoxin-infused quarters were at increased risk for positive assay results, compared with noninfused composite samples. Samples collected from endotoxin-infused quarters or control quarters were at increased risk for positive assay results following the intramammary infusion of endotoxin. Our findings suggest that specificity of milk antimicrobial drug residue assays varies greatly among assay kits and that intramammary inflammation may increase the proportion of false-positive assay results.

Free access
in Journal of the American Veterinary Medical Association

SUMMARY

Immunoglobulin reactions to Salmonella dublin in serum and milk from 4 groups of lactating cows were measured by an indirect elisa. The groups consisted of (1) cows that were natural carriers of S dublin in the mammary gland, (2) experimentally infected cows that did not become carriers, (3) cows inoculated with a commercial S dublin bacterin, and (4) cows used as S dublin-negative controls. Milk and serum samples were obtained at monthly intervals. Models for predicting carrier status were developed by use of stepwise logistic regression. Independent variables consisted of serum and milk IgG and IgM titers to S dublin lipopolysaccharide and a ratio of IgG to IgM. The utility of a single sample vs multiple samples obtained at 1-month or 2-month intervals was tested by comparison of goodness-of-fit χ2 P values for 8 models predicting carrier status.

Immunoglobulin reactions specific to S dublin were a significant predictor of carrier status (P < 0.001). Serum IgG titers specific for S dublin were the most important variable for predicting carrier status. Two serum IgG titers to S dublin obtained 2 months apart was a better predictor of carrier status than measurement of the IgG:IgM ratio from a single serum sample. Immunoglobulin recognizing S dublin epitopes also were detected in milk samples. In milk, performing 2 ELISA 60 days apart to determine IgG and IgM reactions to S dublin appeared to be useful for the prediction of carrier status, but was not as accurate as models for serum immunoglobulin reactions.

Free access
in American Journal of Veterinary Research

SUMMARY

Logistic regression was used to develop models predicting preweaning survival in 334 neonatal swine. Measured risk factors included birth weight, litter size (live born), dam parity, serum IgG concentration, serum elisa titers recognizing common gram-negative core antigens, and serum concentrations of the third component of complement. Larger birth weights were associated with increased probability of preweaning survival. The highest mortality was observed in litters with more than 12 pigs. Pigs with serum concentration of the third component of complement (C3) in the lowest stratum, < 20% adult pooled C3 standard (APC3), had reduced mortality, compared with high (> 38% APC3) and middle (20 to 38% APC3) groups. Associations between all other variables, including total serum IgG concentration and preweaning survival were not significant. Few pigs had hypogammaglobulinemia, < 3% of the study population had serum IgG concentrations < 1 g/dl. Of all measured variables, only birth weight and dam parity were significant predictors of preweaning gain. Larger pigs and pigs born to third or greater parity dams had more preweaning gain than other pigs.

Free access
in American Journal of Veterinary Research

Abstract

Objective—To compare the results of regulatory screening and confirmation assays with those of highperformance liquid chromatography (HPLC) in the detection of ceftiofur metabolites in the tissues of culled dairy cattle.

Animals—17 lactating Holstein dairy cows.

Procedure—Daily IM injections of ceftiofur sodium were administered at a dose of 2.2 mg of ceftiofur equivalents/kg (n = 6) or 1.0 mg of ceftiofur equivalents/kg (10) for 5 days. Following withdrawal times of 12 hours (high-dose ceftiofur) and either 5 or 10 days (low-dose ceftiofur), cows were slaughtered and liver, kidney, and diaphragmatic muscle specimens were harvested and analyzed by HPLC and standard regulatory methods that included the following assays: the swab test on premises, the fast antimicrobial screen test, the calf antibiotic and sulfa test, and the 7-plate bioassay confirmation test.

Results—In all tissue specimens, residues of ceftiofur and desfuroylceftiofur-related metabolites, as measured by HPLC, were less than regulatory tolerance, as defined by the FDA. False-positive screening assay results were more likely for tissue specimens that had been frozen for shipment to a federal laboratory, compared with fresh tissue specimens that were assayed at the slaughter establishment (23% vs 3% false-positive results, respectively).

Conclusions and Clinical Relevance—The observation that fresh tissues had negative results on screening assays, whereas subsets of the same tissue specimens had false-positive results on screening assays following freezing, suggests that freezing and thawing interferes with microbial inhibition-based regulatory screening assays. (Am J Vet Res 2004;65:1730–1733)

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in American Journal of Veterinary Research