Analysis of within-pen and between-pen fenceline temporal contact networks in confined feedlot cattle.

Though contact networks are important for describing the dynamics for disease transmission and intervention applications, individual animal contact and barriers between animal populations, such as fences, are not often utilized in the construction of these models. The objective of this study was to use contact network analysis to quantify contacts within two confined pens of feedlot cattle and the shared "fenceline" area between the pens at varying temporal resolutions and contact duration to better inform the construction of network-based disease transmission models for cattle within confined-housing systems. Two neighboring pens of feedlot steers were tagged with Real-Time Location System (RTLS) tags. Within-pen contacts were defined with a spatial threshold (SpTh) of 0.71 m and a minimum contact duration (MCD) of either 10 seconds (10 s), 30 seconds (30 s), or 60 seconds (60 s). For the fenceline network location readings were included within an area extending from 1 m on either side of the shared fence. "Fenceline" contacts could only occur between a steer from each pen. Static, undirected, weighted contact networks for within-pen networks and the between-pen network were generated for the full study duration and for daily (24-h), 6-h period, and hourly networks to better assess network heterogeneity. For the full study duration network, the two within-pen networks were densely homogenous. The within-pen networks showed more heterogeneity when smaller timescales (6-h period and hourly) were applied. When contacts were defined with a MCD of 30 s or 60 s, the total number of contacts seen in each network decreased, indicating that most of the contacts observed in our networks may have been transient passing contacts. Cosine similarity was moderate and stable across days for within pen networks. Of the 90 total tagged steers between the two pens, 86 steers (46 steers from Pen 2 and 40 steers from Pen 3) produced at least one contact across the shared fenceline. The total network density for the network created across the shared fenceline between the two pens was 17%, with few contacts at shorter timescales and for MCD of 30 s or 60 s. Overall, the contact networks created here from high-resolution spatial and temporal contact observation data provide estimates for a contact network within commercial US feedlot pens and the contact network created between two neighboring pens of cattle. These networks can be used to better inform pathogen transmission models on social contact networks.

Estimation of foot-and-mouth disease windborne transmission risk from USA beef feedlots.

Windborne spread of foot-and-mouth disease (FMD) requires specific epidemiological and meteorological conditions, thus modeling the risk of windborne spread involves integrating epidemiological and meteorological models. The objective of this study was to investigate the potential risk of windborne spread of FMD from an infected US feedlot using an integrated modeling approach, and to identify factors that determine this risk. To address this objective, we integrated a within-herd epidemiological model and an advanced atmospheric dispersion model, and calculated infection risk dependent on exposed herd size. A previously developed epidemiological model was used to simulate the spread of FMD through a typical U.S. feedlot, while the National Oceanic and Atmospheric Administration's (NOAA) HYSPLIT atmospheric dispersion model, which has been validated for FMD modeling, was used to model virus dispersion. Infection risk for exposed herds was calculated as a binomial probability accounting for dose and exposed herd size. We modeled risk of windborne spread from a typical 4000 head feedlot in the U.S. state of Iowa (IA), and a typical 48,000 head feedlot in the U.S. state of Kansas (KS) during winter and summer seasons. The risk of windborne spread of FMD varied based on weather/season conditions, estimated average viral shedding rate per head, size of infected herd, and size of exposed herd. In the baseline Kansas scenario (KS/103/W), the median of the maximum daily risk of infecting a 1000-head exposed herd ranged from 58.16 % at 1 km to 0.78 % at 10 km (Table 4). In the baseline Iowa scenario (IA/103/W), the median of the maximum daily risk of infecting a 1000-head exposed herd ranged from 21.78 % at 1 km to 0.05 % at 10 km (Table 4). The minimum control area recommended by the United States Department of Agriculture (USDA) in an FMD outbreak is 10 km from the infected premise. Our results indicate that significant risk of windborne spread may extend beyond 10 km in certain situations. This is particularly a concern in areas where there are large feedlots in relatively close proximity, such as in southwestern Kansas. Our model may be useful as a research tool in the absence of an outbreak and may help direct surveillance and response efforts in the event of an outbreak.

Spatial and network analysis of U.S. livestock movements based on Interstate Certificates of Veterinary Inspection.

Livestock movements are a common pathway for the spread infectious diseases in a population. An understanding of livestock movement patterns is needed to understand national transmission risks of highly infectious diseases during epidemics. Social Network Analysis (SNA) is an approach that helps to describe the relationships among individuals and the implications of those relationships. We used SNA to describe the contact structure of livestock movements throughout the contiguous U.S. from April 1st, 2015 to March 31st, 2016. We describe 4 network types: beef cattle, dairy cattle, swine, and small ruminant. Livestock movement data were sourced from Interstate Certificates of Veterinary Inspection (ICVI) while county-level farm demographic data were from the National Agricultural Statistics Service (NASS). In the described networks, nodes are represented by counties and arcs by shipments between nodes; the networks were weighted based on the number of shipments between nodes. For the analyses, movement data were aggregated at the county level and on an annual basis. Measures of centrality and cohesiveness were computed and identification of trade-communities in all networks was conducted. During the study period, a total of 219,042 movements were recorded and beef cattle movements accounted for 63 % of all movements. At least 70 % of U.S. counties were present in each of the networks, but the density of arcs was less than 2% in all networks. In the beef cattle network, counties with high out-degree were strongly correlated (0.8) with the number of beef cows per county while for the dairy cattle network a strong correlation (>0.86) was found with the number of dairy cattle per km2 at the county level. All networks were found to have between 4 and 6 large communities (50 counties or more per community), and were geographically clustered except for the communities in the small ruminant network. Outputs reported in these analyses can help to understand the structure of the contact networks for beef cattle, dairy cattle, swine, and small ruminants. They may also be used in conjunction with simulation modeling to evaluate spread of highly infectious disease such as foot-and-mouth disease at the national level and to evaluate the application of intervention strategies.

A deterministic, dynamic systems model of cow-calf production: The effects of breeding replacement heifers before mature cows over a 10-year horizon.

Some cattle production experts believe that cow-calf producers should breed replacement heifers (nulliparous cows) before cows (primiparous and multiparous cows), sometimes referred to as providing a heifer lead time (tHL). Our objective was to model the effects different durations of tHL may have on measures of herd productivity, including the percent of the herd cycling before the end of the first 21 d of the breeding season (%C21), the percent of the herd pregnant at pregnancy diagnosis (%PPD), the distribution of pregnancy by 21-d breeding intervals, the kilograms of calf weaned per cow exposed (KPC), and the replacement percentage (%RH), using a deterministic, dynamic systems model of cow-calf production over a 10-yr horizon. We also wished to examine differences in the effect of tHL related to the primiparous duration of postpartum anestrus (dPPA). The study model examined 6 different dPPA for primiparous cows (60, 70, 80, 90, 100, or 110 d). The multiparous cow duration of postpartum anestrus was set to 60 d. The breeding season length for nulliparous cows was 63 d, as was the breeding season length for primiparous and multiparous cows. Nulliparous cows were modeled with a tHL of 0, 7, 14, 21, 28, 35, or 42 d. Results are reported for the final breeding season of the 10-yr horizon. Increasing tHL resulted in a greater %C21 for the herd and for primiparous cows. Length of tHL had minimal impact on the %PPD unless the dPPA was 80 d or greater. For a dPPA of 110 d, a 0 d tHL resulted in the herd having 88.1 %PPD. When tHL was 21 d, the %PPD increased to 93.0%. The KPC was 161.2 kg when the dPPA was 110 d and tHL was 0 d and improved to 183.2 kg when tHL was increased to 42 d. The %RH did not vary much unless the dPPA was 90 d or greater, but increasing tHL resulted in decreased %RH. Based on the model results, increasing tHL improves the production outcomes included in the analysis, but herds with dPPA of 90 d or greater had the greatest degree of improvement. For these herds, approximately two-thirds of the improvement in outcomes by increasing tHL from 0 d to 42 d was realized when tHL was 21 d. Costs are likely incurred when implementing tHL in a breeding management program, and an ideal tHL likely depends on the dPPA of the herd, the expected improvement in productivity, and the costs associated with increasing tHL. Determining the dPPA of a herd could help veterinarians and producers develop optimal herd management strategies.

A deterministic, dynamic systems model of cow-calf production: The effects of the duration of postpartum anestrus on production parameters over a 10-year horizon.

The duration of postpartum anestrus (dPPA) is important to consider for reproductive performance and efficiency in cow-calf operations. We developed a deterministic, dynamic systems model of cow-calf production over a 10-yr horizon to model the effects that dPPA had on measures of herd productivity, including the percentage of cows cycling before the end of the first 21 d of the breeding season (%C21), the percentage of cows pregnant at pregnancy diagnosis (%PPD), the distribution of pregnancy by 21-d breeding intervals, the kilograms of calf weaned (KW), the kilograms of calf weaned per cow exposed (KPC), and the replacement percentage. A 1,000-animal herd was modeled, with the beginning and ending dates for a 63-d natural service breeding season being the same for eligible replacement heifers (nulliparous cows) and cows (primiparous and multiparous cows). Herds were simulated to have a multiparous cow dPPA of 50, 60, 70, or 80 d, with the dPPA for primiparous cows being set to 50, 60, 70, 80, 90, 100, or 110 d. Only combinations where the primiparous dPPA was greater than or equal to the multiparous dPPA were included, resulting in 22 model herds being simulated in the analysis. All other model parameters were held constant between simulations. In model season 10, the %C21 was 96.2% when the multiparous cow and primiparous cow dPPA was 50 d and was 48.3% when the multiparous cow and primiparous cow dPPA was 80 d. The %PPD in model season 10 for these same herds was 95.1% and 86.0%, respectively. The percentage of the herd becoming pregnant in the first 21 d of the breeding season also differed between these herds (61.8% and 31.3%, respectively). The 10-yr total KW was more than 275,000 kg greater for the herd with a 50-d multiparous cow and primiparous cow dPPA when compared with the herd with the 80-d multiparous and primiparous cow dPPA and had a model season 10 KPC of 180.8 kg compared with 151.4 kg for the longer dPPA. The model results show that both the multiparous cow and primiparous cow dPPA affect herd productivity outcomes and that a dPPA less than 60 d results in improved production outcomes relative to longer dPPA. Veterinarians and producers should consider determining the dPPA to aid in making management decisions to improve reproductive performance of cow-calf herds.

The Effect of Chinese rhubarb, Rheum officinale, with and without benazepril on the progression of naturally occurring chronic kidney disease in cats.

BACKGROUND: Renal fibrosis is common in progressive kidney disease. Transforming growth factors ß (TGF-ß) are important mediators of all types of fibrosis, including renal fibrosis. Chinese rhubarb has been shown to have antifibrotic properties in part because of inhibition of TGF-ß and has slowed the progression of kidney disease in rodent models. HYPOTHESIS: That administration of a Chinese rhubarb supplement will slow the progression of chronic kidney disease (CKD) in cats and the concurrent administration of Chinese rhubarb and benazepril will be more effective than either alone. ANIMALS: Twenty-nine client-owned cats with naturally occurring IRIS Stage 2 or early Stage 3 CKD and without comorbidity such as cancer, urinary tract obstruction, urinary tract infection, poorly controlled hyperthyroidism, or systemic hypertension were enrolled in the study. METHODS: A randomized, positive-controlled, prospective study was performed. Cats received Chinese rhubarb, benazepril, or both in addition to standard treatment for CKD. Repeated measures ANOVA was used to assess changes in serum creatinine concentration, body weight, hematocrit, urine protein: urine creatinine ratio (UPC), and systemic arterial blood pressure over time between and within treatment groups over an average of 22 months. RESULTS: No significant differences were detected in serum creatinine concentration, body weight, hematocrit, UPC, and systemic arterial pressure over time between or within treatment groups. CONCLUSIONS AND CLINICAL IMPORTANCE: This study failed to detect a significant difference in the progression of CKD in cats treated with Chinese rhubarb, benazepril, or both. Further study in specific subsets of cats with CKD is warranted.

Prevalence and relatedness of Escherichia coli O157:H7 strains in the feces and on the hides and carcasses of U.S. meat goats at slaughter.

We determined the prevalences of Escherichia coli O157:H7 in feces, hide, and carcasses of meat goats at a U.S. processing plant. Prevalences were 11.1%, 2.7%, and 2.7%, respectively. Sixteen pulsed-field gel electrophoresis (PFGE) subtypes were identified among 49 E. coli O157:H7 isolates, some of which were present on multiple sample types or collection days.

Associations between the presence and magnitude of Escherichia coli O157 in feces at harvest and contamination of preintervention beef carcasses.

To quantify associations at slaughter between Escherichia coli O157 carcass contamination, fecal-positive animals, and high-shedding animals within truckloads of finished cattle, we sampled up to 32 cattle from each of 50 truckloads arriving at a commercial abattoir in the Midwest United States during a 5-week summer period. Carcass swab samples collected pre-evisceration and fecal samples collected postevisceration were matched within animals and analyzed for the presence of E. coli O157, using enrichment, immunomagnetic separation, and plating on selective media (IMS). In addition, a direct plating procedure was performed on feces to identify high-shedding animals. E. coli O157 was isolated from 39 (2.6%) of 1,503 carcass samples in 15 (30%) truckloads, and 127 (8.5%) of 1,495 fecal samples in 37 (74%) truckloads. Fifty-five (3.7%) high-shedding animals were detected from 26 (52%) truckloads. Truckload high-shedder (Spearman rank-order correlation coefficient [r(s)] = 0.68), IMS-positive (r(s) = 0.48), and combined fecal (r(s) = 0.61) prevalence were significantly correlated with carcass prevalence. The probability of isolating E. coli O157 from a carcass was not significantly associated with the high-shedder or fecal IMS status of the animal from which the carcass was derived. However, the probability of carcass contamination was significantly associated with all truckload-level measures of fecal E. coli O157, particularly whether or not a high shedder was present within the truckload (odds ratio = 16.2; 95% confidence interval, 6.3-43.6). Our results suggest that high shedders within a truckload at slaughter could be a target for mitigation strategies to reduce the probability of preevisceration carcass contamination.

Sensitivity of direct plating for detection of high levels of E. coli O157:H7 in bovine fecal samples.

To assess the sensitivity of direct plating of bovine fecal samples for detection of Escherichia coli O157:H7, calves (n = 28) were orally inoculated with 10(9) colony-forming units (cfu) per calf of a mixture of three strains of nalidixic acid-resistant E. coli O157:H7, and fecal samples were collected for analysis. One-gram samples from inoculated calves were mixed with 9 mL of Gram-negative broth with vancomycin, cefixime, and cefsoludin. From this suspension, serial dilutions were made (10(-1) to 10(-4)) and spread plated in triplicate on Sorbitol MacConkey agar with nalidixic acid for enumeration of E. coli O157:H7 in fecal samples. Direct plating samples were streaked for isolation on Sorbitol MacConkey agar with cefixime, and tellurite (SMACct). After incubation overnight at 37 degrees C, morphologically typical colonies from direct streak plates were plated onto blood agar and incubated overnight at 37 degrees C; then an indole test was performed on each colony. Indole-positive colonies were confirmed by O157 agglutination and were then plated on SMAC agar with 20 microg/mL nalidixic acid (SMACnal) to confirm nalidixic acid resistance. Overall sensitivity of detection was 32.5% (110/338 samples). Sensitivity to detect fecal samples shedding at above 5 x 10(4) cfu/g was 83% (71/86 samples). Based on these data, direct plating of fecal samples might be an effective way to identify cattle that are likely to be shedding E. coli O157 at high levels.

Pulsed-field gel electrophoresis patterns of Escherichia coli O157 isolates from Kansas feedlots.

This study investigated the prevalence and distribution of Escherichia coli O157 genetic types within and among feedlots using pulsed-field gel electrophoresis to separate XbaI-digested DNA. The study population consisted of 300 pens of cattle in 30 feedlots in Kansas that were sampled (feces, water, and water sediment) within a month of being shipped for slaughter. The prevalence of E. coli O157 was 8.5% in feces, 3.1% in water, and 4.5% in water sediment samples. A total of 424 E. coli O157 isolates were characterized by pulsed-field gel electrophoresis, and 139 subtypes (100% Dice similarity with no band differences) were identified. The majority of subtypes (70/139) was identified only once, but nine were identified 10 or more times. Identical subtypes were recovered from both feces and water tanks in 10 feedlots. The majority of subtypes were identified in only one feedlot, and the number of subtypes ranged from one to 23 within a feedlot and from one to seven within a pen. There were 10 feedlots with at least 15 positive samples. In these 10 feedlots, the most common subtype accounted for 16.9-78.6% of the isolates. Common subtypes differed among feedlots. In eight of the 10 feedlots, the most common subtype was identified in multiple pens. The results support a complex ecology for E. coli O157 in feedlot operations, with factors associated with exposure and transmission likely acting at a common level for multiple feedlots, within feedlots, and within pens of cattle.

Effect of pooling bovine fecal samples on the sensitivity of detection of E. coli O157:H7.

To assess the effect of pooling fecal samples on the sensitivity of detection of E. coli O157:H7, 12 calves, inoculated orally with 10(8)cfu per calf of nalidixic acid resistant E. coli O157:H7, were used to provide positive fecal samples. After inoculation, calves were sampled twice weekly. Negative fecal samples were from calves at a local dairy. Samples from inoculated calves were incubated without pooling or were mixed with known negative fecal samples in a 1:4 ratio or a 2:3 ratio (positive:negative) for detection of E. coli O157:H7. Samples were enriched 6h in Gram negative broth with vancomycin, cefixime, and cefsoludin, underwent immunomagnetic separation with Dynabeads, and were plated onto sorbitol MacConkey agar with cefixime, and tellurite (SMACct). Morphologically typical colonies were plated onto blood agar, incubated overnight at 37 degrees C and an indole test was performed on each colony. Indole positives colonies were plated on SMAC agar with 20 microg/ml nalidixic acid (SMACnal). Colonies that grew on SMACnal were confirmed by O157 agglutination. Sensitivity of detection in non-pooled samples was 77%. Samples pooled 1:4 and 2:3 with negative samples were 55 and 52% sensitive, respectively. Pooling decreased sensitivity of detection for E. coli O157:H7 in bovine fecal samples (P<0.01). A deterministic binomial probability model was developed to assess the probability of detecting pens of cattle shedding E. coli O157 using a pooling protocol or individual samples. Pooling decreased sensitivity of detection at low pen prevalence compared to individual samples but was similar at high prevalence.

Escherichia coli O157 in feedlot cattle feces and water in four major feeder-cattle states in the USA.

The prevalence of Escherichia coli O157 was determined in 10662 fecal samples, 2130 water and 1132 water tank-sediment samples collected during the summer months in 2001 from 711 pens in 73 feedlots located in Kansas, Nebraska, Texas, or Oklahoma, USA. Overall, 10.2% of fecal samples were positive for E. coli O157, with 52% of the pens and 95.9% of the feedlots having at least one positive fecal sample. There were no differences among states or months in the fecal prevalences. Water or water tank-sediment was positive in 13.1% of the water tanks, and 60.3% of feedlots had at least one positive tank. Cattle were more likely to be shedding E. coli O157 in pens with positive water tanks, and water was more likely to be positive when E. coli O157 was detected in the sediment.

Prevalence and reproductive effects of Ureaplasma diversum in beef replacement heifers and the relationship to blood urea nitrogen level.

A systematic sample of replacement heifers from 5 herds underwent prebreeding vaginal swab cultures for Ureaplasma diversum. Heifers from three of the herds were subsequently sampled at pregnancy examination. Sampled heifers were given a vaginal lesion score (VLS), reproductive tract score (RTS) and body condition score (BCS), and peripheral blood was collected for serum blood urea nitrogen (BUN) estimation. Culture results revealed an overall prevalence of Ureaplasma diversum of 51% (87/171) at prebreeding and 65% (64/98) at pregnancy examination. Within herd prevalence ranged from 36% to 64% at prebreeding and 54% to 76% at pregnancy examination. Prevalence tended to differ between herds (P=0.08). At the prebreeding examination, heifers with a BCS of 5.5 or less were more likely to be culture positive than heifers with a BCS greater than 5.5 (p<0.05). No relationship was noted between BUN, VLS, RTS, or pregnancy status and prebreeding culture status. There was little variability among the heifers for any of these variables, with vaginal lesion scores generally being mild, RTS scores being high and BCS scores being moderate. At pregnancy examination, heifers that were culture negative tended to be more likely to be pregnant (odds 3.7, p=0.10) than culture positive heifers.

Biosecurity practices of beef cow-calf producers.

OBJECTIVE: To evaluate biosecurity practices of cow-calf producers. DESIGN: Cross-sectional survey. SAMPLE POPULATION: 2,713 cow-calf operations were used in phase 1 of the study, and 1,190 cow-calf operations were used in phase 2. PROCEDURE: Producers were contacted for a personal interview between Dec 30, 1996 and Feb 3, 1997 regarding their management practices. Noninstitutional operations with 1 or more beef cows were eligible to participate in the study. Producers who participated in the first phase of the study and who had > or = 5 beef cows were requested to continue in the study and were contacted by a veterinarian or animal health technician who administered further questionnaires. All contacts for the second phase of the study were made between Mar 3, 1997 and Apr 30, 1997. Additional data on use of various vaccines, testing of imported cattle for brucellosis, Mycobacterium paratuberculosis, bovine viral diarrhea, and tuberculosis as well as potential for feed contamination were collected during the second phase of the study. RESULTS: Producers commonly engaged in management practices that increased risk of introducing disease to their cattle such as importing cattle, failing to quarantine imported cattle, and communal grazing. Producers inconsistently adjusted for the increased risk of their management practices by increasing the types of vaccines given, increasing the quarantine time or proportion of imported animals quarantined, or increasing testing for various diseases in imported animals. CONCLUSIONS AND CLINICAL RELEVANCE: Cow-calf herds are at risk for disease exposure from outside sources when cattle are introduced to the herd, and producers do not always adjust management practices such as vaccination schedules and quarantine procedures appropriately to minimize this risk. Veterinary involvement in education of producers regarding biosecurity risks and development of rational and economical biosecurity plans is needed.

Neospora caninum seroprevalence and associated risk factors in beef cattle in the northwestern United States.

A Neospora caninum seroprevalence and risk factor survey of 2585 cows was conducted in 55 beef cow-calf herds located in five northwestern states of the USA. Blood samples were collected by private veterinary practitioners and management practices were surveyed using a mail questionnaire. Producers were randomly selected from those that employed these veterinarians to perform annual herd pregnancy examinations. Questions were asked about animal management, grazing and feeding, immunization and record keeping practices. Blood was collected from a systematically selected sample of cows in each herd, and age, origin, and pregnancy status were recorded. Blood samples were analyzed for antibodies against N. caninum antigen using a monoclonal antibody-based competitive inhibition (CI) ELISA. Overall seroprevalence was 24% and within herd seroprevalence ranged from 3 to 67% with a median of 19%. Within herd seroprevalence and mean inhibition percentage were different between the five states. Herds that managed their cows on range for summer grazing had lower seroprevalence than those that did not, while increased seroprevalence was associated with higher winter stocking density. Cows less than 3 years of age had higher CI ELISA inhibition percent values than cows greater than 6 years of age. No relationship was noted between serologic status and individual cow origin (purchased or raised), or pregnancy status at the time of sampling.

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.

Fecal Escherichia coli O157:H7 shedding patterns of orally inoculated calves.

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.

Veterinary involvement in management practices of beef cow-calf producers.

Management practices of 53 beef cow-calf producers were surveyed by use of a mail questionnaire. Producers were randomly selected from those who employ veterinarians to perform herd pregnancy examinations. Questions were asked about animal management, grazing and feeding, vaccination, and record-keeping practices. Median herd size was 250 breeding cows, and 2,329 of 2,491 (93%) randomly sampled cows in these herds were pregnant. Less than half of producers associated with these herds reported adoption of many beneficial practices related to bull management, infectious disease management, nutrition, and individual-animal record keeping, suggesting that a considerable number of producers are missing opportunities to optimize production and, thus, economic return. Use of individual-animal production records, which would enable more objective decision making on the basis of production and economic data, was not widespread. These findings suggested that veterinarians serving beef ranches have opportunities to provide additional services incorporating these management practices.

Sensitivity of bacteriologic culture for detection of Escherichia coli O157:H7 in bovine feces.

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.