Distribution of Culicoides sonorensis (Diptera: Ceratopogonidae) in Nebraska, South Dakota, and North Dakota: clarifying the epidemiology of bluetongue disease in the northern Great Plains region of the United States.

The presence or absence of the biting midge Culicoides sonorensis Wirth & Jones (Diptera: Ceratopogonidae), a primary vector of bluetongue viruses (genus Orbivirus, family Reoviridae, BTV) in North America, was assessed on ranches and farms across the Northern Great Plains region of the United States, specifically Nebraska, South Dakota, and North Dakota, as part of a 2-yr regional study of BTV exposure among cattle. Blacklight/suction trap samples totaling 280 2-night intervals were taken at 140 aquatic sites (potential larval habitat for C. sonorensis) on 82 livestock operations (ranches and farms) that span a south-to-north gradient of expected decreasing risk for exposure to BTV. In Nebraska, C. sonorensis populations were common and widespread, present at 15 of 18 operations. Of 32 operations sampled in South Dakota, seven of which were sampled in successive years, 18 were positive for C. sonorensis; 13 of 14 operations located west of the Missouri River were positive, whereas 13 of 18 operations east of the river were negative. Of 32 operations sampled in North Dakota, seven of which were sampled both years, 12 were positive for C. sonorensis. Six of eight operations located west and south of the Missouri River in North Dakota were positive, whereas 18 of 24 operations east and north of the river were negative for C. sonorensis. These data illustrate a well-defined pattern of C. sonorensis spatial distribution, with populations consistently present across Nebraska, western South Dakota, and western North Dakota; western South Dakota, and North Dakota encompass the Northwestern Plains Ecoregion where soils are nonglaciated and evaporation exceeds precipitation. In contrast, C. sonorensis populations were largely absent east of the Missouri River in South Dakota and North Dakota; this area comprises the Northwestern Glaciated Plains Ecoregion and Northern Glaciated Plains Ecoregion where surface soils reflect Wisconsinan glaciation and precipitation exceeds evaporation. In defining a well-demarcated pattern of population presence or absence on a regional scale, the data suggest that biogeographic factors regulate the distribution of C. sonorensis and in turn BTV exposure. These factors, ostensibly climate and soil type as they affect the suitability of larval habitat, may explain the absence of C. sonorensis, hence limited risk for exposure to BTV, across the eastern Northern Plains, upper Midwest, and possibly Northeast, regions of the United States.

Prevalence, species distribution and antimicrobial resistance of enterococci isolated from US dairy cattle.

AIMS: To estimate prevalence and antimicrobial susceptibility of enterococci in faeces collected in 2007 from U.S. dairy cattle. METHODS AND RESULTS: A total of 718 faecal samples from 122 dairy cattle operations from 17 US States were collected and cultured for the presence of enterococci. One hundred and eighteen of the 122 operations (96·7%) had at least one dairy cow positive for enterococci and 88·7% (637 of 718) of the faecal samples were positive. At least ten different enterococcal species were found on the dairy operations and 90·7% (107 of 118) of the operations were positive for Enterococcus hirae followed by E. faecalis (40·7%; 48 of 118) and E. faecium (39%; 46 of 118). The highest percentage of resistant isolates were to lincomycin (92·3%; 587 of 636), flavomycin (71·9%; 457 of 636) and tetracycline (24·5%; 156 of 636). Multi-drug resistance (MDR) (resistance ≥ 2 antimicrobials) was observed to as many as seven antimicrobials regardless of class. CONCLUSION: In contrast to previous studies, faecal shedding of enterococci in dairy cattle occurred in almost 90% of cows sampled and represented a variety of enterococcal species. SIGNIFICANCE AND IMPACT OF STUDY: Although this study demonstrated a high prevalence of antimicrobial-resistant enterococci from dairy cattle faeces in the United States, the contribution of dairy cattle as a source of antimicrobial-resistant enterococci that can be transmitted to humans remains unclear.

Arterial blood gas parameters of normal foals born at 1500 metres elevation.

REASONS FOR PERFORMING STUDY: Arterial blood gas analysis is widely accepted as a diagnostic tool to assess respiratory function in neonates. To the authors' knowledge, there are no published reports of arterial blood gas parameters in normal neonatal foals at altitude. OBJECTIVE: To provide information on arterial blood gas parameters of normal foals born at 1500 m elevation (Fort Collins, Colorado) in the first 48 h post partum. HYPOTHESIS: Foals born at 1500 m will have lower PaO2 and PaCO2 than foals born at sea level due to low inspired oxygen and compensatory hyperventilation occurring at altitude. METHODS: Sixteen foals were studied. Arterial blood gas analysis was performed within 1 h of foaling and subsequent samples were evaluated at 3, 6, 12, 24 and 48 h post partum. Data were compared to those previously reported in healthy foals born near sea level. RESULTS: Mean PaO2 was 53.0 mmHg (7.06 kPa) within 1 h of foaling, rising to 67.5 mmHg (9.00 kPa) at 48 h post partum. PaCO2 was 44.1 mmHg (5.88 kPa) within one hour of foaling, falling to 38.3 mmHg (5.11 kPa) at 48 h. Both PaO2 and PaCO2 were significantly lower in foals born at 1500 m elevation than those near sea level at several time points during the first 48 h. CONCLUSIONS AND POTENTIAL RELEVANCE: Foals at 1500 m elevation undergo hypobaric hypoxia and compensatory hyperventilation in the first 48 h. Altitude specific normal arterial blood values are an important reference for veterinarians providing critical care to equine neonates.

Impact of transportation and lairage on hide contamination with Escherichia coli O157 in finished beef cattle.

Transportation of cattle from the feedlot to the slaughter plant could influence hide contamination of Escherichia coli O157. A study was initiated to investigate the influence of transportation and lairage on shedding and hide contamination of E. coli O157. Fecal and hide samples were obtained from 40 pens of harvest-ready beef cattle at the feedlot prior to transport and again at the slaughter plant immediately after slaughter. Potential risk factors for hide contamination at the feedlot, during transport, and at slaughter were evaluated. A multilevel Poisson regression model was used to evaluate if transportation and lairage were associated with hide contamination by E. coli O157 in finished beef cattle. Lots of cattle held in E. coli O157-positive lairage pens had eight times greater risk of having positive slaughter hide samples compared with cattle held in culture-negative pens (relative risk, 8.0; 95% confidence interval, 1.6 to 38.8). Lots of cattle that were held in lairage pens contaminated with feces had three times greater risk for positive slaughter hide samples compared with cattle held in clean pens (relative risk, 3.1; 95% confidence interval, 1.2 to 7.9). Lots of cattle that were transported for long distances (> 160.9 km) had twice the risk of having positive hide samples at slaughter compared with cattle transported a shorter distance (relative risk, 2.4; 95% confidence interval, 1.1 to 5.1). These findings suggest that transportation and lairage should be considered in E. coli O157 control strategies.

Risk associated with transportation and lairage on hide contamination with Salmonella enterica in finished beef cattle at slaughter.

Transportation of cattle to the slaughter plant could influence hide contamination with Salmonella enterica. Fecal and hide samples were obtained from 40 lots of cattle at the feedlot and again at the slaughter plant. Potential risk factors for hide contamination were evaluated. A multilevel Poisson regression model was used to determine whether transportation and lairage were associated with hide contamination by Salmonella. Cattle with hide samples positive for Salmonella at the feedlot had twice the risk of having positive slaughter hide samples compared with cattle without positive feedlot hide samples (relative risk [RR], 1.9). Cattle transported in trailers from which samples positive for Salmonella were collected had twice the risk of having positive slaughter hide samples compared with cattle transported in culture-negative trailers (RR, 2.3). Cattle transported for long distances had twice the risk of having positive hide samples at slaughter compared with cattle transported shorter distances (RR, 2.3). Cattle held in lairage pens contaminated with feces had twice the risk of having positive slaughter hide samples compared with cattle held in clean pens (RR, 1.8). Cattle held off feed longer than 18 h before loading had twice the risk of having positive slaughter hide samples compared with cattle held off feed for shorter times (RR, 1.7). Cattle that were agitated during loading had twice the risk of having positive slaughter hide samples compared with cattle that were calm (RR, 2.2). These findings suggest that variables associated with transportation and lairage can impact the presence of Salmonella on the hides of cattle at slaughter.

Prevalence of serum antibodies to bovine herpesvirus-1 and bovine viral diarrhea virus in beef cattle in Uruguay.

Our objective was to determine the prevalence of serum antibodies to bovine herpesvirus-1 (BHV-1) and bovine viral diarrhea (BVD) virus in beef cattle in Uruguay. A random sample of 230 herds selected with probability proportional to population size based on the number of cattle was chosen from a list frame of all registered livestock farms as of June 1999. Sera from up to 10 heifers, cows and bulls (up to 30 sera total per herd) were collected on selected farms between March 2000 and March 2001 and evaluated by means of enzyme-linked immunosorbent assays (ELISAs). Overall, 6358 serum samples were evaluated. We also collected data on previous diagnosis of BHV-1 or BVD infections and on the use of vaccines against these agents. The estimated prevalence of exposure to BHV-1 and BVD at the herd level for the Uruguayan beef population was 99% and 100%, respectively. Approximately 37% of beef cattle in Uruguay have been exposed to BHV-1 and 69% to BVD virus. Only 3% of beef herds in Uruguay regularly (typically, annually) use vaccines against either of these agents.

Genotypic and epidemiologic characterization of extended-spectrum cephalosporin resistant Salmonella enterica from US beef feedlots.

In the US, nontyphoidal Salmonellae are a common foodborne zoonotic pathogen causing gastroenteritis. Invasive Salmonella infections caused by extended-spectrum cephalosporin resistant (ESCR) phenotypes are more likely to result in treatment failure and adverse health outcomes, especially in severe pediatric Salmonella infections where the extended-spectrum ß-lactams are the therapy of choice. To examine the genetic and epidemiologic characteristics of ESCR Salmonellae which may enter the food chain, we characterized 44 ceftiofur-resistant Salmonella isolates from the National Animal Health Monitoring System (NAHMS) 2011 beef cattle feedlot health and management study. As part of the NAHMS Feedlot 2011 study, 5050 individual fecal samples from 68 large (1000+ head capacity) feedlots were cultured for Salmonella spp. The resulting 460 positive samples yielded 571 Salmonella isolates with 44 (8%) expressing an AmpC ß-lactamase phenotype. These phenotypic blaCMY-2Salmonella isolates represented 8 serotypes, most commonly S. Newport (n=14, 32%), S. Typhimurium (n=13, 30%), and S. Reading (n=5, 11%), followed by S. Dublin, S. Infantis, S. Montevideo, S. Rough O:i;v:1;7, and S. Uganda. Carriage of the blaCMY-2 gene was confirmed for all isolates expressing an AmpC ß-lactamase phenotype by PCR. Additionally, all 44 isolates were shown to carry the blaCMY-2 gene on a large IncA/C plasmid, a gene/plasmid combination which has been previously reported in multiple species. Other plasmids, including IncN, FIC, and FIIA, were also detected in some isolates. Cattle fed chlortetracycline were less likely to be positive for a blaCMY-2Salmonella isolate in their enteric flora compared to those not receiving chlortetracycline during the feeding period. Carriage of blaCMY-2 was more prevalent in Salmonella isolates originating from lighter weight cattle, cattle fed tylosin and dairy breeds. Our characterization of the NAHMS Feedlot 2011 study Salmonella isolates with ESCR phenotype shows that while other cephalosporin resistance mechanisms have been reported in US cattle, specific serotypes harboring blaCMY-2 on IncA/C plasmids may be the dominant resistance genotype.

Antimicrobial susceptibility of Clostridium difficile isolated from food animals on farms.

Clostridium difficile is commonly associated with a spectrum of disease in humans referred to as C. difficile-associated disease (CDAD) and use of antimicrobials is considered a risk factor for development of disease in humans. C. difficile can also inhabit healthy food animals and transmission to humans is possible. As a result of the complexity and cost of testing, C. difficile is rarely tested for antimicrobial susceptibility. A total of 376 C. difficile strains (94 each from swine and dairy feces, and 188 from beef cattle feces) were isolated from healthy food animals on farms during studies conducted by the National Animal Health Monitoring System. Using the Etest (AB Biodisk, Solna, Sweden), samples were tested for susceptibility to nine antimicrobials implicated as risk factors for CDAD (linezolid, amoxicillin-clavulanic acid, ampicillin, clindamycin, erythromycin, levofloxacin, metronidazole, rifampicin, and vancomycin). Vancomycin was active against all isolates of C. difficile (MIC90=3.0µg/ml) while almost all isolates (n=369; 98.1%) were resistant to levofloxacin. With the exception of vancomycin, resistance varied by animal species as follows: linezolid (8.5% resistance among swine versus 2.1 and 1.1% resistance among dairy and beef, respectively), clindamycin (56.4% resistance among swine versus 80% and 90.9% resistance among dairy and beef, respectively), and rifampicin (2.1% and 0% resistance among swine and dairy cattle isolates, respectively versus 14.3% resistance among beef isolates). Regardless of species, multiple drug resistance was observed most often to combinations of clindamycin and levofloxacin (n=195; 51.9%) and ampicillin, clindamycin and levofloxacin (n=41; 10.9%). The reason for the variability of resistance between animal species is unknown and requires further research.

Salmonella in dairy operations in the United States: prevalence and antimicrobial drug susceptibility.

Salmonella serotypes are important foodborne pathogens of humans that can be acquired through consumption of contaminated meat and dairy products. Salmonella infection also can be a significant animal health issue. As part of a national study of U.S. dairy operations conducted between March and September 2002, fecal samples were collected from representative cows in 97 dairy herds in 21 states and were cultured to determine the prevalence of Salmonella shedding. Salmonella was recovered from the feces of at least one cow in 30.9% of the herds. Overall, 7.3% of fecal samples were culture positive for Salmonella. The three most frequently recovered serotypes were Salmonella Meleagridis (24.1%), Salmonella Montevideo (11.9%), and Salmonella Typhimurium (9.9%). The susceptibilities of Salmonella isolates recovered were determined using a panel of 16 antimicrobial drugs. Salmonella isolates recovered from dairy cows had relatively little resistance to these antimicrobial agents; 83.0% of the isolates were susceptible to all antimicrobials tested. This study provides updated information on the prevalence and susceptibility patterns of Salmonella in dairy herds and on cow and herd characteristics. These data contribute to our understanding of the ecology of Salmonella in the dairy farm environment.

Comparison of mixed effects models of antimicrobial resistance metrics of livestock and poultry Salmonella isolates from a national monitoring system.

Antimicrobial use in agriculture is considered a pathway for the selection and dissemination of resistance determinants among animal and human populations. From 1997 through 2003 the U.S. National Antimicrobial Resistance Monitoring System (NARMS) tested clinical Salmonella isolates from multiple animal and environmental sources throughout the United States for resistance to panels of 16-19 antimicrobials. In this study we applied two mixed effects models, the generalized linear mixed model (GLMM) and accelerated failure time frailty (AFT-frailty) model, to susceptible/resistant and interval-censored minimum inhibitory concentration (MIC) metrics, respectively, from Salmonella enterica subspecies enterica serovar Typhimurium isolates from livestock and poultry. Objectives were to compare characteristics of the two models and to examine the effects of time, species, and multidrug resistance (MDR) on the resistance of isolates to individual antimicrobials, as revealed by the models. Fixed effects were year of sample collection, isolate source species and MDR indicators; laboratory study site was included as a random effect. MDR indicators were significant for every antimicrobial and were dominant effects in multivariable models. Temporal trends and source species influences varied by antimicrobial. In GLMMs, the intra-class correlation coefficient ranged up to 0.8, indicating that the proportion of variance accounted for by laboratory study site could be high. AFT models tended to be more sensitive, detecting more curvilinear temporal trends and species differences; however, high levels of left- or right-censoring made some models unstable and results uninterpretable. Results from GLMMs may be biased by cutoff criteria used to collapse MIC data into binary categories, and may miss signaling important trends or shifts if the series of antibiotic dilutions tested does not span a resistance threshold. Our findings demonstrate the challenges of measuring the AMR ecosystem and the complexity of interacting factors, and have implications for future monitoring. We include suggestions for future data collection and analyses, including alternative modeling approaches.

Fecal shedding of Salmonella spp. by dairy cows on farm and at cull cow markets.

As part of a national study of the U.S. dairy cow population, fecal samples were collected from representative cows on 91 dairies and 97 cull dairy cow markets in 19 states. Salmonella spp. were recovered from 5.4% of milk cows, 18.1% of milk cows expected to be culled within 7 days, and 14.9% of culled dairy cows at markets. On a premise basis, Salmonella shedding in milk cows was detected on 21.1% of dairies and 66% of cull dairy cow markets. The percentage of herds with at least one cow with detectable Salmonella fecal shedding was higher during the sampling period from May through July, in herds with at least 100 milk cows, and in herds in the South region. The most common Salmonella serogroups isolated were E (30.8% of isolates) and C1 (28.6%); the most common serotypes isolated were Salmonella Montevideo (21.5% of isolates), Salmonella Cerro (13.3%), and Salmonella Kentucky (8.5%). Fecal shedding of Salmonella Typhimurium or Salmonella Typhimurium var. copenhagen was infrequent (2.8% of isolates). Most isolates (88.9%) were susceptible to all 17 antimicrobials evaluated; multiple resistance was an infrequent occurrence. This study provides information describing the distribution of Salmonella fecal shedding from dairy cows on farm and at markets and will serve as a baseline for future studies.

Survey of Salmonella serotypes shed in feces of beef cows and their antimicrobial susceptibility patterns.

Salmonella prevalence on cow-calf operations was studied as a part of a national study of health and management of the U.S. beef cow-calf industry and was conducted as part of the National Animal Health Monitoring System. Within this study, the prevalence of Salmonella spp. shed in feces was determined. A total of 5,049 fecal samples were collected from 187 beef cow-calf operations each visited on a single occasion. The number of fecal samples collected per operation was predetermined based on herd size. Salmonellae were recovered from 1 or more fecal samples collected on 11.2% (21 of 187) of the operations. Overall 78 salmonellae representing 22 serotypes were recovered from 1.4% (70 of 5,049) of samples. Multiple serotypes were recovered from eight samples from a single operation. The five most common serotypes were Salmonella Oranienburg (21.8% of isolates), and Salmonella Cerro (21.8%), followed by Salmonella Anatum (10.3%), Salmonella Bredeney (9.0%), and Salmonella Mbandaka (5.1%). The most common serogroups identified were C1 (33.3%), K (21.8%), B (16.7%), and E (15.4%). Even though the recovery rate of salmonellae from fecal samples was very low, 43.6% (34 of 78) and 38.5% (30 of 78) of the isolates were among the 10 most common serotypes from cattle with clinical signs of disease or isolated from humans, respectively. The majority of the isolates (50 of 78; 64.1%) were recovered from fecal samples from two operations. All isolates were screened for resistance to a panel of 17 antimicrobics, and 87.2% (68 of 78) were susceptible to all of the antimicrobics. The resistant isolates were most commonly resistant to streptomycin (n = 9) and/or sulfamethoxazole (n = 9). Nine isolates showed multiple (> or =2 antimicrobics) resistance most commonly to streptomycin and sulfamethoxazole (n = 6).

Survey of Salmonella serotypes in feedlot cattle.

A national study of health and management of cattle in feedlots was conducted. Within this study, the prevalence of Salmonella spp. in fecal samples was determined. Fifty fecal samples were collected from each of 100 feedlots. Within each feedlot, 25 fresh fecal samples were collected from the floor of the pens of cattle which had been on feed the shortest and 25 from those on feed the longest periods of time. The total number of samples collected was 4,977; 2,484 and 2,495 from pens of cattle on feed the shortest and longest times, respectively. Salmonella spp. were recovered from 38% (38 of 100) of the feedlots. Salmonella spp. were recovered from 5.5% (273 of 4,977) of all samples and from 3.5% (88 of 2,484) and 7.4% (185 of 2,495) of samples from pens of cattle shortest and longest on feed, respectively. The most common serotype recovered was S. anatum (27.9%), followed by S. montevideo (12.9%), S. muenster (11.8%), S. kentucky (8.2%), and S. newington (4.3%). The most common serogroups identified were E1 (39.6%), C1 (20.7%), and B (10.4%). Shedding of the serotypes most commonly associated with human illness occurred infrequently (13 of 273: 4.8%). This study provides information on the status of Salmonella spp. from cattle in feedlots and may serve as baseline information for future studies.

Risk factors for high herd level calf morbidity risk from birth to weaning in beef herds in the USA.

We analyzed data from a national survey of beef cow-calf producers in the USA to quantify the effects of hypothesized risk factors on herd-level calf morbidity risk from birth to weaning. The analysis included 2490 herds from 23 states. Two stepwise logistic regressions were fit to identify factors associated with ≥10% morbidity. The first model included all herds dichotomized into high-morbidity herds with ≥10% morbidity and low-morbidity herds with <10% morbidity. The second model excluded herds with between 5 and 10% morbidity, and compared >/=10% morbidity with 70% of cows and heifers calves in confinement also increased the odds of being a high-morbidity herd (OR=1.8). The population attributable fractions for dystocia and confined calving for the model including all herds dichotomized at 10% morbidity were 0.41 and 0.11, respectively. The summary population attributable fraction for both factors was 0.46.

Foaling-management practices associated with the occurrence of enterocolitis attributed to Clostridium perfringens infection in the equine neonate.

Enterocolitis associated with Clostridium perfringens (C. perfringens) infection in neonatal foals is often severe and has been associated with a high case-mortality risk. We designed a premises-based survey to evaluate the associations of regional foaling practices, premises environmental management, periparturient foal and brood-mare management, and periparturient brood-mare ration with the occurrence of neonatal enterocolitis attributed to C. perfringens infection. Potential risk factors individually associated with enterocolitis were breed type, housing type at foaling and in the first three days of life, ground/floor surface type at foaling and in the first three days of life, brood-mare ration before and after foaling, and the presence of livestock other than horses on the premises in the past. From the multivariable-logistic regression models, six variables were significantly associated with an increased risk of the outcome of interest (p<0.05): foals of the stock horse type, housing in a stall or drylot in the first three days of life, other livestock present on the premises in the past, foal born on dirt, sand or gravel surface, and low amounts of grass hay and grain fed post-partum. Low grain amounts fed pre-partum represented a decreased risk of the outcome of interest.

Vesicular adenitis of bulls: A review.

The prevalence of inflammatory disease of the vesicular glands can be as high as 49% in some groups of bulls under common management conditions. Since these bulls are classified as questionable or unsatisfactory potential breeders, this disease can cause significant economic loss to the producer. The current knowledge of the etiology, pathogenesis, diagnosis, treatment, and prevention are discussed.

Real-time ultrasonography for determining pregnancy status and viable fetal numbers in ewes.

The reproductive tracts of 26 estrus synchronized, bred ewes were scanned with a portable 5.0 MHz real-time ultrasound unit within 1 to 6 d postbreeding. Intrarectal scanning was performed on alternate days until Days 28 to 30 and twice weekly until Days 50 of gestation. Transabdominal uterine scans were conducted twice weekly from Days 25 to 65 and continued weekly until parturition. A total of 24 ewes (92%) became pregnant. A nonpregnant ewe was recognized 100% of the time by both methods of ultrasonic screening. Correct identification of a gravid ewe as pregnant was 100% from Days 51 to 150 of gestation using transabdominal real-time ultrasonography. There was a significant association (P < 0.005) between the number of lambs born and the number of fetuses observed using transabdominal real-time ultrasonography after Day 25 of gestation. Accurate differentiation of fetal numbers by transabdominal scanning was 100.0% for ewes carrying one lamb and 97.3% for ewes carrying two lambs at Days 51 to 75 of gestation. Fetal attrition was documented in one ewe at Day 49 of gestation. Hydrops allantois was diagnosed in another ewe at 110 d of gestation. A total of 37 lambs were born to 23 ewes in the project flock. No congenital abnormalities were noted in any of the lambs. Transabdominal real-time ultrasonography is a safe, rapid, accurate and practical method for assessing pregnancy status, fetal number and fetal viability in sheep.

A retrospective study of vein thrombosis in horses treated with intravenous fluids in a veterinary teaching hospital.

The medical records of 68 horses treated with IV fluids for 24 hours or more were reviewed to determine the risk of vein thrombosis and to determine which factors were associated with the occurrence of vein thrombosis in these horses. Three factors were positively associated with vein thrombosis including use of locally produced fluids and presence of fever and diarrhea. Two factors, having general anesthesia or having surgery, were negatively associated with vein thrombosis. One continuous variable, duration of treatment, was positively associated with vein thrombosis. Factors not associated with vein thrombosis included breed, age, sex, type of catheter, outcome (lived or died), laminitis, colic, other drugs via the catheter, and type of surgery. One type of catheter was used in the majority of horses (57) making it difficult to detect effect of catheter type. Preparation of the catheter site, the person placing the catheter, and technique of catheter maintenance were not evaluated. Like all retrospective studies, this study has limitations to the conclusions that can be made; however, the strong association between source of fluids, fever, diarrhea, anesthesia/surgery, and the occurrence of vein thrombosis merits consideration in the clinician's therapeutic plan.

The risks and prevention of contamination of beef feedlot cattle: the perspective of the United States of America.

There are currently no scientifically defined critical management points or critical control points to manage foodborne pathogens at the pre-harvest level. Research is ongoing: much of the pre-harvest research is funded by producer organisations. The beef industry has Beef Quality Assurance (BQA) programmes in place and these are dynamic. Groups of cattlemen have made a very strong commitment to reducing foodborne pathogens in beef. Fewer Escherichia coli O157:H7 organisms are shed by feedlot cattle near the end of the feeding period than by newly arrived cattle. Moreover, there is less shedding of the organisms in cattle of slaughter age than in younger cattle. The prevalence of E. coli O157:H7 in feedlot cattle is similar to that in range cattle. This suggests that concentrating cattle in feedlot dirt pens does not increase the risk of shedding E. coli organisms. Pen maintenance, considered a good management practice, appears to be an adequate means of keeping pathogen levels in pens low. It is not likely that pre-harvest food safety programmes will eliminate the threat of pathogens such as E. coli O157:H7 or Salmonella. The management of foodborne pathogens will become part of an integrated programme to enhance food safety which includes the producer, the packer, the distributors, retailers and the consumer. The feedlot industry initiated a residue avoidance programme several years ago. As a result, the risk of chemical residues in beef from feedlots in the United States of America is near zero. Hazard analysis and critical control point-type prevention programmes, using scientifically based critical management points, will help ensure that the risk remains negligible.

A comparison of dobutamine infusion to exercise as a cardiac stress test in healthy horses.

This study was done to determine whether administration of dobutamine would produce echocardiographic and electrocardiographic alterations comparable to those induced by treadmill exercise in healthy horses. Fourteen horses received maximal treadmill exercise and, separately, intravenous dobutamine infusion up to a maximum rate of 50 microg/kg/min. Ten of the 14 horses were euthanized, and the myocardial tissues were examined grossly and histopathologically. No significant differences were found in the chronotropic effects of dobutamine and exercise (P = .905). Dobutamine induced greater interventricular septal thickening during systole (dobutamine = 4.78 cm, exercise = 4.03 cm; P = .004). and greater left ventricular diameters during diastole (dobutamine = 9.73 cm, exercise = 9.26 cm; P = .037), than did exercise treatment. Horses exhibited transient signs of sweating and restlessness during infusion of moderate to maximum doses of dobutamine. Ventricular ectopy seen in 11 of 14 horses was attributed to the arrhythmogenic properties of dobutamine, as well as to increased vagal tone present at low dobutamine doses. Myocardial lesions characteristic of catecholamine myotoxicity were present in 2 of the 10 horses examined. Although dobutamine induces chronotropic and inotropic changes similar to those induced by exercise, the use of high-dose dobutamine as a cardiac stressor in horses cannot be advocated because of potential development of arrhythmias or myotoxicity.