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Salmonella Cerro prevalence in US dairy cattle has increased significantly during the past decade. Comparison of 237 Salmonella isolates collected from various human and animal sources between 1986 and 2009 using pulsed-field gel electrophoresis, antimicrobial resistance typing, and spvA screening, showed very limited genetic diversity, indicating clonality of this serotype. Improved subtyping methods are clearly needed to analyze the potential emergence of this serotype. Our results thus emphasize the critical importance of population-based pathogen surveillance for the detection and characterization of potentially emerging pathogens, and caution to critically evaluate the adequacy of diagnostic tests for a given study population and diagnostic application., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Salmonella represents an important zoonotic pathogen worldwide, but the transmission dynamics between humans and animals as well as within animal populations are incompletely understood. We characterized Salmonella isolates from cattle and humans in two geographic regions of the United States, the Pacific Northwest and the Northeast, using three common subtyping methods (pulsed-field gel electrophoresis [PFGE], multilocus variable number of tandem repeat analysis [MLVA], and multilocus sequence typing [MLST]). In addition, we analyzed the distribution of antimicrobial resistance among human and cattle Salmonella isolates from the two study areas and characterized Salmonella persistence on individual dairy farms. For both Salmonella enterica subsp. enterica serotypes Newport and Typhimurium, we found multidrug resistance to be significantly associated with bovine origin of isolates, with the odds of multidrug resistance for Newport isolates from cattle approximately 18 times higher than for Newport isolates from humans. Isolates from the Northwest were significantly more likely to be multidrug resistant than those from the Northeast, and susceptible and resistant isolates appeared to represent distinct Salmonella subtypes. We detected evidence for strain diversification during Salmonella persistence on farms, which included changes in antimicrobial resistance as well as genetic changes manifested in PFGE and MLVA pattern shifts. While discriminatory power was serotype dependent, the combination of PFGE data with either MLVA or resistance typing data consistently allowed for improved subtype discrimination. Our results are consistent with the idea that cattle are an important reservoir of multidrug-resistant Salmonella infections in humans. In addition, the study provides evidence for the value of including antimicrobial resistance data in epidemiological investigations and highlights the benefits and potential problems of combining subtyping methods.

Objective: To describe geographic, farm-type, and animal-type factors associated with multiple antimicrobial resistance (MAR) in fecal Escherichia coli isolates from cattle., Design: Cross-sectional field study., Sample Population: 1,736 fecal samples from cattle on 38 farms in California, Oregon, and Washington., Procedures: Fecal samples were collected from preweaned calves (2 to 4 weeks old) and cows that recently calved on dairy and beef cow-calf farms, preweaned calves on calf ranches, and 1-year-old steers on feedlots. One fecal E coli isolate per sample was isolated, and antimicrobial susceptibility was tested. Escherichia coli isolates were initially clustered by antimicrobial resistance patterns and categorized by number of antimicrobial resistances. A generalized estimating equations cumulative logistic regression model was used to identify factors associated with an increase in MAR in fecal E coli isolates from cattle., Results: MAR was higher in E coli isolates from cattle in California, compared with those from cattle in Washington or Oregon. Multiple antimicrobial resistance was highest in E coli isolates from calves on calf ranches and progressively lower in isolates from feedlot steers, dairy cattle, and beef cattle. Multiple antimicrobial resistance was higher in E coli isolates from calves than from adult cattle, in E coli isolates from cattle of conventional farms than of organic farms, and in isolates from beef cattle in intensive dairy farm regions than from beef cattle distant from dairy farm regions., Conclusions and Clinical Relevance: MAR in fecal E coli isolates from cattle was influenced by factors not directly associated with the use of antimicrobials, including geographic region, animal age, and purpose (beef vs dairy).

Fifty-nine commercial dairy farms were sampled 7 times over 15 to 21 mo to determine the role of animal movement, including off-farm rearing of heifers, in the interherd transmission of multidrug-resistant (MDR) Salmonella spp. Farm management data were collected by on-site inspections and questionnaires on herd management practices before and after the study. Forty-four percent (26/59) of herds did not acquire any new MDR Salmonella strains. The number of newly introduced MDR Salmonella strains acquired by the remaining 56% (33/59) of herds ranged from 1 to 8. Logistic regression models indicated that off-farm heifer raising, including contract heifer raising where heifers commingle with cattle from other farms [commingled heifers, odds ratio (OR) = 8.9, 95% confidence interval (CI): 2.4, 32.80], and herd size per 100-animal increment (herd size, OR = 1.04, 95% CI, 1.01, 1.05) were significantly associated with the introduction of new MDR Salmonella strains. The negative binomial regression similarly revealed that commingled heifers [relative risk (RR) = 2.3, 95% CI: 1.1, 4.7], herd size per 100 animals (RR = 1.02, 95% CI, 1.01, 1.03), and a history of clinical salmonellosis diagnosed before the study (RR = 2.5, 95% CI, 1.3, 5.0) were significantly associated with the number of new MDR Salmonella strains that were introduced. Factors not associated with the introduction of new MDR Salmonella strains were housing of heifers and cows in the same close-up pen, a common hospital-maternity pen, and the number of purchased cattle. This study highlights the role of animal movement in the interherd transmission of MDR Salmonella spp.

A longitudinal observational study of 59 dairy herds was conducted in Washington State to estimate the rate of introduction of new multidrug-resistant (MDR) Salmonella enterica strains onto commercial dairy herds. Samples were collected on these herds over 7 visits separated by intervals of 2 to 4 mo over a period of 15 to 21 mo. Samples were cultured for Salmonella spp. and serogroup, serovar, and antimicrobial susceptibility patterns were identified for MDR Salmonella isolates. Fingerprinting generated by pulsed-field gel electrophoresis (PFGE) using XbaI restriction enzyme digestion generated genotyping profiles for all MDR isolates identified in the study. The rate of new MDR Salmonella strain introduction was 0.9 per herd-year (95% confidence interval: 0.6-1.4). The rates for the most commonly introduced MDR Salmonella serovars were 0.4/herd-year for Typhimurium, 1.2/herd-year for Newport, and 0.1/herd-year for Dublin. Thirty-three of 59 herds (56%) had at least one new MDR Salmonella introduction during the study period. The number of new MDR Salmonella strains acquired by dairy herds ranged from zero to 8. Thirteen of the 59 herds had a history of clinical salmonellosis. Among these 13 herds, 6 herds acquired new MDR Salmonella strains, although these strains were different than historical clinical strains. These data indicate that acquisition of new MDR Salmonella strains by dairy herds was a common event in participating herds, although the number of strains introduced varied greatly among herds.

Escherichia coli O157:H7 genotypes in the bovine reservoir may differ in virulence. The proportion of clinical genotypes among cattle isolates was weakly (P = 0.054) related to the international incidence of E. coli O157:H7-associated hemolytic-uremic syndrome, varied among clinical isolates internationally, and also differed along the putative cattle-hamburger-clinical case transmission chain.

The purpose of this study was to investigate the genetic similarity of Campylobacter jejuni and Campylobacter coli with similar antimicrobial resistance phenotypes, isolated from cattle on different farms and at different times, in order to evaluate the possible existence of disseminated antimicrobial resistant clones. PFGE after SmaI and KpnI restriction identified 23 and 16 distinct PFGE patterns among 29 C. jejuni and 66 C. coli isolates, respectively. In C. coli, 51 (77%) of the resistant isolates demonstrated one of the four indistinguishable PFGE patterns, whereas only 24% doxycycline resistant C. jejuni shared one of the two indistinguishable PFGE patterns. The genetic mechanisms of resistance were homogeneous within and between these clonal types. Genetically indistinguishable (clonal) groups of C. coli accounted for most Campylobacter sp. with multiple antimicrobial resistance observed in this study, consistent with a role for clonal dissemination in the epidemiology of resistance in this species.

Feedlot cattle were observed for fecal excretion of and rectoanal junction (RAJ) colonization with Escherichia coli O157:H7 to identify potential "supershedders." RAJ colonization and fecal excretion prevalences were correlated, and E. coli O157:H7 prevalences and counts were significantly greater for RAJ samples. Based on a comparison of RAJ and fecal ratios of E. coli O157:H7/E. coli counts, the RAJ appears to be preferentially colonized by the O157:H7 serotype. Five supershedders were identified based on persistent colonization with high concentrations of E. coli O157:H7. Cattle copenned with supershedders had significantly greater mean pen E. coli O157:H7 RAJ and fecal prevalences than noncopenned cattle. Cumulative fecal E. coli O157:H7 excretion was also significantly higher for pens housing a supershedder. E. coli O157:H7/E. coli count ratios were higher for supershedders than for other cattle, indicating greater proportional colonization. Pulsed-field gel electrophoresis analysis demonstrated that isolates from supershedders and copenned cattle were highly related. Cattle that remained negative for E. coli O157:H7 throughout sampling were five times more likely to have been in a pen that did not house a supershedder. The data from this study support an association between levels of fecal excretion of E. coli O157:H7 and RAJ colonization in pens of feedlot cattle and suggest that the presence of supershedders influences group-level excretion parameters. An improved understanding of individual and population transmission dynamics of E. coli O157:H7 can be used to develop preslaughter- and slaughter-level interventions that reduce contamination of the food chain.

Salmonella enterica serovar Dublin (S. Dublin) is a cattle-adapted Salmonella serovar, so if antimicrobial resistance in S. Dublin arises as a result of antimicrobial use this most likely occurs within the cattle reservoir without impact from antimicrobial use in humans. We tested the antimicrobial resistance of bovine-origin S. Dublin isolates from 1986 through 2004 using a standard disk diffusion method. High proportions of isolates throughout the time period were resistant to one or more antimicrobials, and a marked increase in resistance to ceftazidime occurred between 2000 and 2004. Dairy-origin isolates were more likely to be resistant to several antibiotics than were isolates from beef operations where exposure to antimicrobials is likely to be less frequent. Plasmid analysis of a subset of isolates also supported the hypothesis that antimicrobial resistance traits in the cattle-adapted serovar Dublin were acquired within the bovine host environment.

Objective: To evaluate the association between maintaining joint hospital and maternity pens and persistence of multi-drug-resistant (MDR) Salmonella enterica serovar Newport on 2 dairy farms., Design: Observational study., Sample Population: Feces and environmental samples from 2 dairy herds., Procedure: Herds were monitored for fecal shedding of S enterica Newport after outbreaks of clinical disease. Fecal and environmental samples were collected approximately monthly from pens housing sick cows and calving cows and from pens containing lactating cows. Cattle shedding the organism were tested serially on subsequent visits to determine carrier status. One farm was resampled after initiation of interventional procedures, including separation of hospital and maternity pens. Isolates were characterized via serotyping, determination of antimicrobial resistance phenotype, detection of the CMY-2 gene, and DNA fingerprinting., Results: The prevalence (32.4% and 33.3% on farms A and B, respectively) of isolating Salmonella from samples from joint hospital-maternity pens was significantly higher than the prevalence in samples from pens housing preparturient cows (0.8%, both farms) and postparturient cows on Farm B (8.8%). Multi-drug-resistant Salmonella Newport was isolated in high numbers from bedding material, feed refusals, lagoon slurry, and milk filters. One cow excreted the organism for 190 days. Interventional procedures yielded significant reductions in the prevalences of isolating the organism from fecal and environmental samples. Most isolates were of the C2 serogroup and were resistant to third-generation cephalosporins., Conclusions and Clinical Relevance: Management practices may be effective at reducing the persistence of MDR Salmonella spp in dairy herds, thus mitigating animal and public health risk.

Maintenance of antimicrobial drug resistance in bacteria can be influenced by factors unrelated to direct selection pressure such as close linkage to other selectively advantageous genes and secondary advantage conveyed by antimicrobial resistance genes in the absence of drug selection. Our previous trials at a dairy showed that the maintenance of the antimicrobial resistance genes is not influenced by specific antimicrobial selection and that the most prevalent antimicrobial resistance phenotype of Escherichia coli is specifically selected for in young calves. In this paper we examine the role of secondary advantages conveyed by antimicrobial resistance genes. We tested antimicrobial-susceptible null mutant strains for their ability to compete with their progenitor strains in vitro and in vivo. The null mutant strains were generated by selection for spontaneous loss of resistance genes in broth supplemented with fusaric acid or nickel chloride. On average, the null mutant strains were as competitive as the progenitor strains in vitro and in newborn calves (in vivo). Inoculation of newborn calves at the dairy with antimicrobial-susceptible strains of E. coli did not impact the prevalence of antimicrobial-resistant E. coli. Our results demonstrate that the antimicrobial resistance genes are not responsible for the greater fitness advantage of antimicrobial-resistant E. coli in calves, but the farm environment and the diet clearly exert critical selective pressures responsible for the maintenance of antimicrobial resistance genes. Our current hypothesis is that the antimicrobial resistance genes are linked to other genes responsible for differential fitness in dairy calves.

The prevalence of Campylobacter jejuni in commercial feedlot cattle was monitored throughout the feeding period by repeated bacteriologic culture of feces. Fecal pats (n = 10) in 20 feedlot pens were sampled at 2-weeks interval beginning at entry into the feedlot and continuing until slaughter. The least-squares mean C. jejuni prevalence increased from 1.6% at the first sampling to 61.3% at the final sampling just prior to slaughter. Diverse C. jejuni pulsed-field gel electrophoresis macrorestriction profiles (MRP) were identified among the cattle isolates, but five prevalent MRP and minor variants accounted for >80% of all typed isolates. Chlorination of the water supplied to the water troughs of half of the pens did not affect C. jejuni prevalence in the cattle. Overall, the least-squares mean C. jejuni prevalences were 45.6 and 43.6% in chlorinated and nonchlorinated feedlot pens, respectively. The results of this study demonstrate apparent transmission of C. jejuni among feedlot cattle during the feeding period, unaffected by water chlorination, resulting in a high prevalence of C. jejuni excretion by cattle approaching slaughter.

The prevalence of thermophilic Campylobacter spp. was investigated in cattle on Washington State farms. A total of 350 thermophilic Campylobacter isolates were isolated from 686 cattle sampled on 15 farms (eight dairies, two calf rearer farms, two feedlots, and three beef cow-calf ranches). Isolate species were identified with a combination of phenotypic tests, hipO colony blot hybridization, and multiplex lpxA PCR. Breakpoint resistance to four antimicrobials (ciprofloxacin, nalidixic acid, erythromycin, and doxycycline) was determined by agar dilution. Campylobacter jejuni was the most frequent species isolated (34.1%), followed by Campylobacter coli (7.7%) and other thermophilic campylobacters (1.5%). The most frequently detected resistance was to doxycycline (42.3% of 350 isolates). Isolates from calf rearer facilities were more frequently doxycycline resistant than isolates from other farm types. C. jejuni was most frequently susceptible to all four of the antimicrobial drugs studied (58.8% of 272 isolates). C. coli isolates were more frequently resistant than C. jejuni, including resistance to quinolone antimicrobials (89.3% of isolates obtained from calves on calf rearer farms) and to erythromycin (72.2% of isolates obtained from feedlot cattle). Multiple drug resistance was more frequent in C. coli (51.5%) than in C. jejuni (5.1%). The results of this study demonstrate that C. jejuni is widely distributed among Washington cattle farms, while C. coli is more narrowly distributed but significantly more resistant.

The prevalence of antimicrobial drug-resistant bacteria is typically highest in younger animals, and prevalence is not necessarily related to recent use of antimicrobial drugs. In dairy cattle, we hypothesize that antimicrobial drug-resistant, neonate-adapted bacteria are responsible for the observed high frequencies of resistant Escherichia coli in calves. To explore this issue, we examined the age distribution of antimicrobial drug-resistant E. coli from Holstein cattle at a local dairy and conducted an experiment to determine if low doses of oxytetracycline affected the prevalence of antimicrobial drug-resistant E. coli. Isolates resistant to tetracycline (>4 microg/ml) were more prevalent in <3-month-old calves (79%) compared with lactating cows (14%). In an experimental trial where calves received diets supplemented with or without oxytetracycline, the prevalence of tetracycline-resistant E. coli was slightly higher for the latter group (P = 0.039), indicating that drug use was not required to maintain a high prevalence of resistant E. coli. The most common resistance pattern among calf E. coli isolates included resistance to streptomycin (>12 microg/ml), sulfadiazine (>512 microg/ml), and tetracycline (>4 microg/ml) (SSuT), and this resistance pattern was most prevalent during the period when calves were on milk diets. To determine if prevalence was a function of differential fitness, we orally inoculated animals with nalidixic acid-resistant strains of SSuT E. coli and susceptible E. coli. Shedding of SSuT E. coli was significantly greater than that of susceptible strains in neonatal calves (P < 0.001), whereas there was no difference in older animals (P = 0.5). These data support the hypothesis that active selection for traits linked to the SSuT phenotype are responsible for maintaining drug-resistant E. coli in this population of dairy calves.

The use of antimicrobial drugs in livestock is suspected to contribute to bacterial antimicrobial resistance (AR) development. Dairy farms experiencing recent outbreaks of salmonellosis involving multi-resistant (MR) Salmonella strains were compared to control farms with respect to AR among bovine commensal E. coli isolates. For most antimicrobials tested, the percentage of AR E. coli isolated from salmonellosis-affected farms was significantly higher than that from control farms. Calf E. coli from both case and control farms had greater levels of AR than cow isolates. Commensal E. coli isolates from case farms and calves tended to more frequently be MR. These data are consistent with the existence of higher antimicrobial selection pressure on farms with recent salmonellosis outbreaks, however, the directionality of the relationship remains to be elucidated. An improved understanding of the epidemiology of AR bacteria in livestock production, both at the herd and molecular level, is essential to mitigate risk to public health and food safety.

Identification of the sources and methods of transmission of Escherichia coli O157:H7 in feedlot cattle may facilitate the development of on-farm control measures for this important food-borne pathogen. The prevalence of E. coli O157:H7 in fecal samples of commercial feedlot cattle in 20 feedlot pens between April and September 2000 was determined throughout the finishing feeding period prior to slaughter. Using immunomagnetic separation, E. coli O157:H7 was isolated from 636 of 4,790 (13%) fecal samples in this study, with highest prevalence earliest in the feeding period. No differences were observed in the fecal or water trough sediment prevalence values of E. coli O157:H7 in 10 pens supplied with chlorinated drinking water supplies compared with nonchlorinated water pens. Pulsed-field gel electrophoresis of XbaI-digested bacterial DNA of the 230 isolates obtained from eight of the pens revealed 56 unique restriction endonuclease digestion patterns (REDPs), although nearly 60% of the isolates belonged to a group of four closely related genetic subtypes that were present in each of the pens and throughout the sampling period. The other REDPs were typically transiently detected, often in single pens and on single sample dates, and in many cases were also closely related to the four predominant REDPs. The persistence and predominance of a few REDPs observed over the entire feeding period on this livestock operation highlight the importance of the farm environment, and not necessarily the incoming cattle, as a potential source or reservoir of E. coli O157:H7 on farms.

Environmental survival of Escherichia coli O157 may play an important role in the persistence and dissemination of this organism on farms. The survival of culturable and infectious E. coli O157 was studied using microcosms simulating cattle water troughs. Culturable E. coli O157 survived for at least 245 days in the microcosm sediments. Furthermore, E. coli O157 strains surviving more than 6 months in contaminated microcosms were infectious to a group of 10-week-old calves. Fecal excretion of E. coli O157 by these calves persisted for 87 days after challenge. Water trough sediments contaminated with feces from cattle excreting E. coli O157 may serve as a long-term reservoir of this organism on farms and a source of infection for cattle.

Escherichia coli O157 isolates from cattle in Japan (n = 91) and in the USA (n = 415) were compared by pulsed-field gel electrophoresis of endonuclease-cleaved genomic DNA, location of the stx genes and bacteriophage typing. Three isolates from cattle in Japan with high similarity to isolates from cattle in the USA were found. Isolates from cattle farms in Japan and the USA may share a common source.

To assess the duration of fecal shedding upon initial infection, the duration of shedding after subsequent re-infection and the effects of dietary restriction and antibiotic treatment on shedding recrudescence, four, one-week-old calves were orally inoculated on three separate occasions with 5x10(8) cfu of Escherichia coli O157:H7 strain 86-24 Nal-R. Fecal shedding was followed by serial culture three times weekly. Following the first inoculation, the calves shed E. coli O157:H7 in their feces for a mean of 30 days, with a range of 20 to 43 days. Following the second and third inoculations, the calves shed E. coli O157:H7 in their feces for 3-8 days. In each of the three inoculations, feed was withheld from the calves for 24 h after they had become fecal culture negative. Two calves resumed shedding, one for 1 day and the other for 4 days, after food was withheld after the third inoculation, but not in the first two inoculations. In the third inoculation, one calf resumed shedding for one day after treatment with oxytetracycline. No E. coli O157:H7 strain 86-24 Nal-R was found in the calves at necropsy. These calves did not exhibit persistent low-level shedding, and did not appear to be persistently colonized with E. coli O157:H7.

This study developed a method to partition the risk of mortality in dairy calves in the 1st 16 weeks of life. Observed population mortality and the relative risk of mortality in each serum protein concentration stratum were used to determine the population baseline mortality rate and the mortality rate due to inadequate passive transfer of colostral immunoglobulin. A total of 3,479 calves were studied, 8.2% of which died before 16 weeks of age. The population baseline mortality rate was 5.0% and the mortality rate due to inadequate passive transfer was 3.2%. Thirty-nine percent of the observed mortality was attributed to inadequate passive transfer. This partitioning of risk between passive transfer-related and unrelated sources should prove useful in conducting investigations of calf mortality problems in dairy herds.

Escherichia coli O157 (n = 376) from 41 cattle farms were subtyped using pulsed field gel electrophoresis of endonuclease cleaved chromosomal DNA. Cleavage with XbaI resulted in 81 subtypes. Fifty-one isolates from subtypes found in more than one herd, or in herds on multiple sample collection dates were compared using the endonuclease NotI, resulting in 23 additional subtypes. Up to 11 XbaI subtypes were found per farm with up to 7 subtypes/farm identified from a single date. Indistinguishable subtypes (both XbaI and NotI) were found to persist on 4 farms for 6-24 months. Five subtypes were found on more than one farm separated by up to 640 km. Dairy farms where cattle had moved onto the farm had a similar number of subtypes as farms with no movement of cattle, and feedlots had more subtypes than dairy farms. These data indicate that there is a mechanism for multiple herd exposure to specific subtypes, there are multiple sources of exposure for cattle on farms, and on-farm reservoirs other than cattle may exist.

The effect of vaccination with a commercially available R-mutant coliform mastitis vaccine on the survival of comingled dairy calves on a farm with endemic salmonellosis was examined. A total of 864 calves were randomly assigned to either vaccine (n = 435) or control (n = 429) groups. Passive transfer status of each calf was determined using refractometer determination of serum total protein concentration. Logistic models were developed to determine the effects of vaccine group and passive transfer status on calf survival to 100 days of age. In a model in which serum protein concentration was treated as a categorical variable, increasing serum total protein concentrations were associated with decreased mortality until these concentrations exceeded 6.0 g/dL. Calves with serum protein concentrations > 6.0 g/dL had increased risk for mortality compared with calves with serum protein concentrations > 5.5 g/dL but < or = 6.0 g/dL. This increased risk for mortality was supported by the results of a logistic model in which serum protein concentration was treated as a continuous variable. The increased risks associated with high serum protein concentration probably reflect the effect of dehydration in calves with occult disease. Neither model demonstrated any significant association between vaccination status and survival to 100 days of age. Based on these results, the routine immunization of calves cannot be recommended as a strategy to prevent mortality on farms with endemic salmonellosis.

An incomplete block split-plot design with repeated measures was used to test the effects of eight combinations of premilking and postmilking teat disinfectants on teat skin and teat end condition over a 6-wk period. These combinations included iodine, sodium chlorite, lactic acid, and orthophosphoric acid. Visual assessments of teat skin and teat ends were made on the teats of 101 cows. Teat skin thickness, teat end thickness, and transepidermal water loss were assessed for the teats of 50 cows. The interaction of predip and postdip had no effect on teat condition. Postdip had a significant effect on transepidermal water loss, visual teat skin condition, and visual teat end condition. The 1% iodine postdip was associated with the poorest teat skin condition.

A split-plot design with repeated measures was used to test the relationship between visual teat skin condition score, the degree of transepidermal water loss from the skin, and the colonization by Staphylococcus aureus on experimentally chapped and inoculated teats of 20 lactating Holstein cows. Visual teat skin chapping score and the number of S. aureus colonies obtained from a teat skin swab were correlated (r = 0.53). Transepidermal water loss and S. aureus count were not correlated (r = 0.02). Results indicated that visual teat skin evaluation is superior to measurements of transepidermal water loss in the prediction of the susceptibility of teat skin to colonization by S. aureus.

Escherichia coli O157 shedding in 14 cattle herds was determined by faecal culture at intervals of approximately 1 month for up to 13 months. The overall prevalence was 1.0% (113/10832 faecal samples) and 9 of the 14 herds were detected as positive. Herds positive 2 years previously (n = 5) had a higher prevalence of positive cattle (median = 1.9%) than herds which had been negative on a previous sampling (n = 8, median = 0.2%). Weaned heifers had a higher prevalence (1.8%) than did unweaned calves (0.9%) or adults (0.4%). For all herds the highest prevalence occurred in the summer months, which resulted in most of the positive faecal samples being collected on a minority of sampling visits.

To better define the bovine reservoir of Escherichia coli O157:H7, cattle were tested monthly by bacteriologic culture for fecal excretion of E. coli. E. coli O157:H7 was isolated from feces of 56 cattle sampled an average of 6.98 times (2-12 samples). By broth enrichment culture, immunomagnetic separation, or both, 35 cattle had 1 positive sample, 12 had 2, 7 had 3, and 1 each had 4 and 5. Five cattle with > or = 2 positive samples were in a herd in which 5 pulsed-field gel electrophoretic (PFGE) types were simultaneously present; in 3 of these cattle, different PFGE types were detected in different samples. The duration of detected excretion E. coli O157:H7 by individual cattle in this study was <1 month in 35 (63%) of 56 cattle. Both serial and concurrent excretion of different E. coli O157:H7 strains by individual cattle was observed.

Objective: To examine the ability of several commonly used tests for evaluation of passive transfer of immunoglobulin to predict mortality in dairy replacement heifers., Design: Prospective observational study., Animals: 246 dairy replacement heifers between 1 and 8 days of age., Procedure: Using serum samples obtained from each calf, total serum protein concentration and results of zinc sulfate turbidity, sodium sulfite turbidity, radial immunodiffusion, and glutaraldehyde coagulation were determined. Calves were monitored for 100 days, and relative risks for death were calculated. Logistic regression models predicting death also were developed., Results: None of the logistic regression models detected a significant association between test results and mortality. The greatest relative risks of mortality were observed in calves with serum protein concentrations < 4.5 g/dl, serum IgG1 concentrations < 500 mg/dl, and sodium sulfite test scores < 1+., Clinical Implications: Calves with lower passive transfer values had increased risk of death; however, failure of passive transfer is not an infallible predictor of mortality.

The sensitivities of several plating and broth enrichment methods for the detection of Escherichia coli O157:H7 in (i) bovine fecal samples directly inoculated with E. coli O157:H7, (ii) fecal samples from cattle in herds previously positive for E. coli O157:H7, and (iii) fecal samples from calves shedding E. coli O157:H7 after experimental oral inoculation were compared. Three enrichment protocols and three plating protocols were evaluated with directly inoculated fecal samples. All broth enrichment methods were superior to direct plating when they were combined with subsequent plating on sorbitol-MacConkey with cefixime and tellurite (SMACct). SMACct was the most sensitive plating medium, and the three alternative broth enrichment methods gave similar improvements in sensitivity. Of 351 fecal samples from known positive herds, 24 samples (6.8%) were positive by one or more methods. By the most sensitive plating method, cultures of 10-g samples were slightly more sensitive (19 of 351 [5.4%]) than cotton-tipped swab fecal samples (14 of 351 [4.0%]); however, this difference was not significant. For samples from calves orally inoculated with E. coli O157:H7, separation by immunomagnetic beads was slightly more sensitive (79%) than broth enrichment followed by plating at two dilutions (10(-3) and 10(-4)) (71%); however, this difference was not significant. The combination of overnight enrichment of swab fecal samples (0.1 g) and plating on SMACct at two dilutions (10(-3) and 10(-4)) appears to be a sensitive method for detection in large-scale studies involving hundreds of samples per week.

Telephone interviews were conducted to evaluate the association of teat chapping with combinations of premilking and postmilking teat disinfectants (predip and postdip), other management practices, and climatic conditions. Holstein dairies (n = 100) in the DHIA SCC program were randomly selected from three northwest regions. During nonwinter seasons, herd managers using an iodophor dip without skin conditioner both premilking and postmilking were 9.7 times more likely to report chapping than were those using iodophor with conditioner. The herd managers least likely to report chapping problems were those using conditioner in both the predip and postdip. Use of conditioner in postdip only was associated with intermediate frequency of reported chapping. No conditioner in either predip or postdip was associated with the greatest frequency of reported chapping. Herd managers using a different germicide in the predip and postdip reported more chapping than herd managers using the same germicide. The frequency of chapping was highest during winter in all regions, and the percentage of herd managers reporting chapping within a region was associated with the temperature extremes of the region. For seasons other than winter, characteristics of predip and postdip combinations and parlor exit or barn design were the management factors that best described an association with reported chapping.

A case-control study was conducted to determine risk factors for fecal shedding of Escherichia coli O157:H7 (ECO) in dairy calves. Three herds previously found to lack calves that shed ECO in their feces were selected for each herd previously found to have calves that shed ECO. Fecal samples from 965 calves on 64 farms were tested for ECO by microbial culture. Sample prevalence of ECO in calves less than 8 weeks old was 1.4% and in calves 8 weeks or older was 4.8%. Calves were 3 times more likely to shed ECO after weaning than before weaning. Shedding of ECO was associated with grouping calves before weaning; feeding whole cottonseed was negatively associated with ECO shedding. The change in results between testing periods illustrated that an individual herd's status cannot be defined by a single testing of a small sample of cattle.

Escherichia coli O157.H7 was found in 10 of 3570 (0.28%) faecal samples from dairy cattle in 5 of 60 herds (8.3%). Several tentative associations with manure handling and feeding management practices on dairy farms were identified. Faecal/urine slurry samples, bulk milk samples, and milk filters from dairy herds were negative for E. coli O157.H7. E. coli O157.H7 was also isolated from 10 of 1412 (0.71%) faecal samples from pastured beef cattle in 4 of 25 (16%) herds. The prevalence of E. coli O157.H7 excretion in feedlot beef cattle was 2 of 600 (0.33%). The identification of cattle management practices associated with colonization of cattle by E. coli O157.H7 suggests the possibility that human E. coli O157.H7 exposure may be reduced by cattle management procedures.

An outbreak of cysticercosis in a south-central Idaho custom feedlot reached a peak prevalence of 11% in January 1993 and extended from October 1992 through March 1993. Of 5,164 cattle slaughtered from this feedlot during the outbreak, 457 (9%) were cysticercosis infected. Total discounts on the infected cattle at slaughter cost the feedlot $154,400. Most evidence was suggestive of feed-borne transmission of Taenia saginata eggs to the cattle in the feedlot. By use of logistic regression analysis of feedlot records, significant (P = 0.004) association of cysticercosis prevalence at slaughter with days on feed was revealed. Similarly, a decline in cysticercosis prevalence was significantly (P < 0.001) related to the number of days cattle were fed a ration not containing potato byproduct. Although sources other than potato byproduct were systematically evaluated during the investigation, findings suggested that potato byproduct fed in this feedlot was contaminated with T saginata eggs.

Forty-eight herds participating in the 1988/1989 Ohio National Animal Health Monitoring System dairy project were monitored for 1 year to determine the effects of environment and management on mortality in preweaned calves. Environmental factors were evaluated by veterinarians during monthly visits to the herds. Management procedures were measured through the use of a questionnaire administered near the end of the project. Mortality in preweaned calves was calculated for each herd by using data from project records on calf mortality and animal inventory, which were collected monthly by veterinarians. Relationships between the management/environment variables and calf mortality were examined by use of analysis of covariance. Herd size, days on a nipple feeder, navel disinfection, type of housing, and whether each calf observed with diarrhea was treated with antibiotics were the variables that had an impact on herd mortality. These variables explained approximately 39% of the variation in mortality among herds.

To estimate herd prevalence of Salmonella spp, fecal specimens were obtained for culture from neonatal calves of 47 Ohio dairy herds. Of the 452 calves tested, 10 calves from 7 farms were culture-positive. Salmonella serotypes isolated were S dublin, S typhimurium, S enteritidis, S agona, S mbandaka, and S montevideo. Bulk tank milk filters from these dairies were also submitted for culture. Salmonella sp was isolated from 1 of the 50 filters, and 2 calves from this herd were found to be shedding Salmonella sp of the same serotype.

Data from slaughter plants (n = 3) and feedlots (n = 18) in eastern Washington were analyzed to characterize occurrence patterns of cysticercosis in Washington during 1984. Three concurrent peaks in cysticercosis rates (0.6/1,000 to 5/1,000 slaughtered cattle) were detected at 3 slaughter plants. Peaks were observed at 8 feedlots from December 1983 to March 1984, at 6 feedlots from April to July 1984, at 2 feedlots from August to October 1984, and at 3 feedlots from November 1984 to February 1985. Affected feedlots were not closely associated geographically and were feeding cattle from many, predominantly northwestern, origins. For 3 feedlots for which time in the feedlot was available for each slaughter shipment, an increase in cysticercosis rate with increasing time in the feedlot was noticed. Within these 3 feedlots, cases of cysticercosis were widely scattered spatially. The pattern of cysticercosis indicated human fecal contamination of a regionally available feed source. Of feedstuffs in use, potato waste, a byproduct of the processed potato industry, appeared to be the most likely source of Taenia saginata ova.

Blood serum immunoglobulin concentrations of calves during their 2nd wk of life had a .97 correlation with 1st wk concentrations. Correlations between 1st wk concentrations and those in the 3rd, 4th, 5th, and 6th wk of life were .91, .90, .81, and .69. Ten herds were divided into those with mortality rates above and below the median. The major difference in distributions of immunoglobulin concentration between the two groups was percent of calves with concentrations less than 2.5 mg/ml during the 1st wk of life. Calves were sampled monthly for a full year in 19 herds, and all but one herd had one or more calves with immunoglobulin concentrations under 5.0 mg/ml. Overall, calves having immunoglobulin concentrations under 5.0 mg/ml were exposed to excess mortality risk; however, most of the excess risk was concentrated in three herds with high mortality rates (16 to 20%). Evaluating the efficiency of passive immune transfer through the use of management data was unreliable in comparison with assaying serum samples for immunoglobulin concentration.

The goal of outbreak investigation is the identification of the risk factors over which management has control; these factors are known as key determinants. The risk factor approach to disease causality is much more functional than simplistic theories such as agent causality. Many outbreaks, even of infectious disease, do not have simple microbiologic explanations. In the planning of an outbreak investigation, the most critical step is the identification of management procedures that have been found, by scientific studies, to influence risk of the type of disease present. During the investigation, specific disease data, rather than the client's impressions, should be collected so that temporal and risk group analyses may be performed. Performance evaluation should be conducted to determine the breadth of management systems involved and the duration of involvement. Management evaluation must be specific, comprehensive, and targeted by scientific studies, risk group and temporal analyses, physical examination, and laboratory diagnosis. The entire investigation--the planning, the data gathering, the sample collection--must be concentrated on identifying the ways in which management should be changed to restore equilibrium to a herd experiencing excessive losses due to disease.