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- Author or Editor: Bruce A. Wagner x
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Objective—To evaluate associations among herd infection status, herd management practices, and familiarity of the herd manager with Mycobacterium paratuberculosis (Johne's disease) or prior disease diagnosis in that herd to support development of Johne's disease-control programs.
Design—Population-based cross-sectional study.
Sample Population—1,004 US dairies, each with ≥ 30 cows, representing 79.4% of US dairy cows.
Procedure—Questionnaires were administered to dairy managers, and blood samples were collected from cows during herd visits. Sera were tested for antibodies to M paratuberculosis, using a commercially available ELISA. Multivariable logistic regression analyses were used to evaluate associations between use of management practices, herd disease status, and familiarity of the manager with Johne's disease or prior diagnosis of Johne's disease in that herd.
Results—Results from serologic testing revealed that 3.4% of cows and 21.6% of dairy herds were infected with M paratuberculosis. Factors associated with infection included number of cows in herd, region of country, percentage of cows born at other dairies, group housing for periparturient cows, and group housing for preweaned calves. Few preventive practices were positively associated with prior diagnosis of Johne's disease (time of separation of newborn calf from dam) or familiarity of the manager with the disease (teats and udder washed before colostrum collected).
Conclusion and Clinical Relevance—Risk factors associated with Johne's disease in this study confirmed those management practices generally recommended for disease control. An educational problem, however, is the finding that herd managers familiar with Johne's disease generally use management practices similar to those used by managers unfamiliar with the disease. (J Am Vet Med Assoc 2000;216:1450–1457)
Objectives—To assess the sensitivity of the current surveillance program used in Denmark for detecting outbreaks of infectious bovine rhinotracheitis (IBR) at the herd level and to evaluate the impact of alternative sample collection strategies on the sensitivity of the system in an acceptable time frame.
Sample Population—Data from the Danish Central Husbandry Register on cattle of 24,355 and 25,233 beef herds and on 13,034 and 12,003 dairy herds in the years 2000 and 2001, respectively.
Procedures—Surveillance programs were evaluated under current sample collection conditions and under 3 alternative scenarios by use of simulation modeling. Data from the current detection component of the surveillance system were used as input, taking into consideration the sensitivity and specificity of bulktank milk and serologic testing.
Results—The current system identifies infected dairy herds within a 3-month period with desired accuracy largely because of the test characteristics and number of bulk-tank milk samples. The system is less likely to detect infected beef herds in a timely manner because surveillance in beef herds depends solely on serologic testing at the time of slaughter. The efficiency of surveillance in dairy cattle herds was not decreased substantially when the slaughter-surveillance component was omitted.
Conclusions and Clinical Relevance—Geographically targeted sample collection during the high-risk season (winter) was predicted to increase the probability of rapid detection of IBR infection in cattle. This approach can be used for assessing other surveillance systems to determine the best strategies for detection of infected herds. (Am J Vet Res 2005;66:2149–2153)
Objective—To evaluate site-to-site variation within fecal pats from cattle with regard to detection of Escherichia coli O157 and determine the effect on the accuracy of prevalence estimates of assay of multiple samples collected from the same fecal pat.
Sample Population—120 freshly voided fecal pats collected from 2 beef feedlots.
Procedures—5 samples were systematically collected from each fecal pat and analyzed for E coli O157 via selective preenrichment techniques, immunomagnetic separation, and biochemical tests. Presumptive isolates were definitively identified via agglutination assays and polymerase chain reaction techniques. Best estimators of prevalence were calculated from the distribution of E coli O157–positive samples per pat.
Results—Of the 120 fecal pats, 96, 13, 4, 2, 3, and 2 fecal pats had 0, 1, 2, 3, 4, and 5 E coli O157–positive samples, respectively. The greatest estimate of E coli O157 prevalence (20%) was achieved when all 5 samples were assessed; this estimate represented a 2.4- fold increase in prevalence, compared with that provided via analysis of 1 sample/pat (8.2%). Compared with assessment of 5 sites/pat, the relative sensitivity of detecting an E coli O157–positive fecal pat via analysis of 1 site/pat was 40.1%.
Conclusions and Clinical Relevance—Results suggest that estimates of E coli O157 prevalence derived from sampling of 1 location/pat are likely underestimates of the true prevalence of this pathogen in fecal pats (and by extension, cattle). Additional research is warranted to confirm these results in situations of high and low prevalence and across different feedlots. (Am J Vet Res 2005;66:2023–2027)
Objective—To evaluate the effectiveness of various sampling techniques for determining antimicrobial resistance patterns in Escherichia coli isolated from feces of feedlot cattle.
Sample Population—Fecal samples obtained from 328 beef steers and 6 feedlot pens in which the cattle resided.
Procedure—Single fecal samples were collected from the rectum of each steer and from floors of pens in which the cattle resided. Fecal material from each single sample was combined into pools containing 5 and 10 samples. Five isolates of Escherichia coli from each single sample and each pooled sample were tested for susceptibility to 17 antimicrobials.
Results—Patterns of antimicrobial resistance for fecal samples obtained from the rectum of cattle did not differ from fecal samples obtained from pen floors. Resistance patterns from pooled samples differed from patterns observed for single fecal samples. Little pen-to-pen variation in resistance prevalence was observed. Clustering of resistance phenotypes within samples was detected.
Conclusions and Clinical Relevance—Studies of antimicrobial resistance in feedlot cattle can rely on fecal samples obtained from pen floors, thus avoiding the cost and effort of obtaining fecal samples from the rectum of cattle. Pooled fecal samples yielded resistance patterns that were consistent with those of single fecal samples when the prevalence of resistance to an antimicrobial was > 2%. Pooling may be a practical alternative when investigating patterns of resistance that are not rare. Apparent clustering of resistance phenotypes within samples argues for examining fewer isolates per fecal sample and more fecal samples per pen. (Am J Vet Res 2002;63:1662–1670)
Objective—To estimate the prevalence of Mycobacterium avium subsp paratuberculosis infection among cows on beef operations in the United States.
Design—Cross-sectional seroprevalence study.
Sample Population—A convenience sample of 380 herds in 21 states.
Procedure—Serum samples were obtained from 10,371 cows and tested for antibodies to M avium subsp paratuberculosis with a commercial ELISA . Producers were interviewed to collect data on herd management practices.
Results—30 (7.9%) herds had 1 or more animals for which results of the ELISA were positive; 40 (0.4%) of the individual cow samples yielded positive results. None of the herd management practices studied were found to be associated with whether any animals in the herd would be positive for antibodies to M avium subsp paratuberculosis.
Conclusions and Clinical Relevance—Results suggest that the prevalence of antibodies to M avium subsp paratuberculosis among beef cows in the United States is low. Herds with seropositive animals were widely distributed geographically. (J Am Vet Med Assoc 2001;219:497–501)
Objective—To determine effects on production and risk of removal related to Mycobacterium avium subsp paratuberculosis (MAP) infection at the individual animal level in dairy cattle.
Animals—7,879 dairy cows from 38 herds in 16 states.
Procedure—A subset of dairy cattle operations that participated in the National Animal Health Monitoring System Dairy 2002 study was evaluated via a serum ELISA for antibodies against MAP and categorized according to ELISA score. Dairy Herd Improvement Association records were obtained to collect current and historical lactation data and removal (ie, culling) information. Production variables were evaluated on the basis of serum ELISA category.
Results—Cows with strong positive results had mature equivalent (ME) 305-day milk production, ME 305-day maximum milk production, and total lifetime milk production that were significantly lower than cows in other categories. No differences were observed for ME 305-day fat and protein percentages, age, lactation, and lactation mean linear somatic cell count score between cows with strong positive results and those with negative results. After accounting for lactation number and relative herd-level milk production, cows with strong positive results were significantly more likely to have been removed by 1 year after testing.
Conclusions and Clinical Relevance—Without management changes designed to reduce the farm-level prevalence of MAP infection, paratuberculosis will continue to reduce farm income by decreasing milk production and potentially increasing premature removal from the herd. (J Am Vet Med Assoc 2005;227:1975–1981)
Objective—To assess associations between herd management practices and herd-level rates of bovine respiratory disease complex (BRDC) in preweaned beef calves in US cow-calf operations.
Sample—443 herds weighted to represent the US cow-calf population.
Procedures—Producers from 24 states were selected to participate in a 2-phase survey; 443 producers completed both survey phases and had calves born alive during the study period. Data from those respondents underwent multivariable negative binomial regression analyses.
Results—Bred heifer importation was associated with lower BRDC rates (incidence rate ratio [IRR], 0.40; confidence interval [CI], 0.19 to 0.82), whereas weaned steer importation was associated with higher BRDC rates (IRR, 2.62; CI, 1.15 to 5.97). Compared with single-breed herds, operations with calves of 2-breed crosses (IRR, 2.36; CI, 1.30 to 4.29) or 3-breed crosses (IRR, 4.00; CI, 1.93 to 8.31) or composite-herd calves (IRR, 2.27; CI, 1.00 to 5.16) had higher BRDC rates. Operations classified as supplemental sources of income had lower BRDC rates (IRR, 0.48; CI, 0.26 to 0.87) than did operations classified as primary sources of income. Reported feed supplementation with antimicrobials was positively associated with BRDC rates (IRR, 3.46; CI, 1.39 to 8.60). The reported number of visits by outsiders in an average month also was significantly associated with herd-level BRDC rates, but the magnitude and direction of the effects varied.
Conclusions and Clinical Relevance—Management practices associated with preweaning BRDC rates may be potential indicators or predictors of preweaning BRDC rates in cow-calf production systems.
Objective—To determine the suitability and estimate the sensitivity of an immunohistochemical (IHC) test for disease-associated prion protein (PrPSc) in biopsy specimens of rectoanal mucosa–associated lymphoid tissue (RAMALT) for diagnosis of scrapie in sheep.
Animals—762 sheep at high risk for having scrapie and indemnified by the National Scrapie Eradication Program.
Procedures—The IHC test for PrPSc was applied to 2 RAMALT and 2 third-eyelid biopsy specimens and a postmortem RAMALT specimen from each sheep. Results were compared with those of a reference test in which results for tissues from obex and retropharyngeal lymph nodes, tonsil, or both were considered in parallel.
Results—The reference test identified 139 sheep as having scrapie. Biopsy-related complications occurred in 3 sheep. Sensitivity of the IHC test in RAMALT ranged from 85.3% to 89.4%, depending on the anatomic location from which RAMALT was obtained. Results for the test applied to 1 RAMALT specimen were similar to results interpreted in parallel for 2 third-eyelid specimens (sensitivity, 87.0%). The proportion of inconclusive test results attributable to insufficient lymphoid follicles in biopsy specimens was lower when considering results for 2 RAMALT specimens in parallel (10.1%) than when considering results for 2 third-eyelid specimens in parallel (23.7%). Specimens of RAMALT that were inappropriately collected from an area caudal to the rectoanal interface yielded a high proportion of inconclusive results (33.3% to 50.0%).
Conclusions and Clinical Relevance—The IHC test for PrPSc in RAMALT was an effective means of detecting subclinical scrapie in live, high-risk sheep.
Objective—To estimate seroprevalence of Mycobacterium avium subsp paratuberculosis (MAP) infection among adult dairy cows in Colorado and determine herd-level factors associated with the risk that individual cows would be seropositive.
Design—Cross-sectional observational study.
Animals—10,280 adult (≥ 2 years old) dairy cows in 15 herds in Colorado.
Procedure—Serum samples were tested with a commercial ELISA. A herd was considered to be infected with MAP if results of mycobacterial culture of ≥ 1 individual cow fecal sample were positive or if ≥ 1 culled cow had histologic evidence of MAP infection.
Results—424 of the 10,280 (4.12%) cows were seropositive. Within-herd prevalence of seropositive cows ranged from 0% to 7.82% (mean, 2.6%). Infection was confirmed in 11 dairies. Cows in herds that had imported ≥ 8% of their current herd size annually during the preceding 5 years were 3.28 times as likely to be seropositive as were cows in herds that imported < 8%. Cows in herds with ≥ 600 lactating cows were 3.12 times as likely to be seropositive as were cows in herds with < 600 lactating cows. Cows in herds with a history of clinical signs of MAP infection were 2.27 times as likely to be seropositive as were cows in herds without clinical signs.
Conclusions and Clinical Relevance—Annual importation rate, herd size, and whether cows in the herd had clinical signs typical of MAP infection were associated with the risk that individual cows would be seropositive for MAP infection. (J Am Vet Med Assoc 2004;225:97–101)