Christine A. Kopral

Prevalence of failure of passive transfer of immunity in newborn heifer calves and associated management practices on US dairy operations.

Failure of passive transfer of immunity (FPT) in dairy replacement calves has been linked to increased neonatal morbidity and mortality and long-term decreases in productivity. The purpose of this study was to estimate the prevalence of FPT in US dairy heifer calves in 2007 and to use nationally representative data to investigate associations of FPT with colostrum and calf management practices. A cross-sectional study was conducted by the USDAs National Animal Health Monitoring System between January and August 2007. Producers from 394 operations in 17 states completed survey questions about colostrum and calf management practices, and serum samples were collected from 1,816 healthy heifer calves on those operations. Serum immunoglobulin G (IgG) levels were determined by radial immunodiffusion, and calves were classified as having FPT if the IgG concentration was less than 10 mg/mL. To investigate associations between FPT and management practices, a multivariable analysis was completed using a weighted logistic regression model. The estimated prevalence of FPT in US dairy heifer calves was 19.2%. The odds of FPT were higher for calves on operations that pooled colostrum [odds ratio (OR = 2.2)], allowed nursing (OR = 2.4), or hand fed colostrum more than 4 h after birth (OR = 2.7). The odds of FPT were also higher for calves on operations that did not provide a source of heat during cold weather for calves experiencing a dystocia (OR = 1.6), would not seek veterinary assistance when unable to correctly position a calf for delivery (OR = 2.6), or did not routinely monitor serum proteins in calves as a measure of passive transfer (OR = 13.8). The prevalence of FPT in dairy heifer calves has decreased in the last 15 yr, so progress has been made in this important area of calf management. This study identified several management practices associated with FPT that could be targeted for educational campaigns or further research.

Prevalence of Salmonella enterica, Listeria monocytogenes, and Escherichia coli Virulence Factors in Bulk Tank Milk and In-Line Filters from U.S. Dairies

The zoonotic bacteria Salmonella enterica, Listeria monocytogenes, and Escherichia coli are known to infect dairy cows while not always causing clinical signs of disease. These pathogens are sometimes found in raw milk, and human disease outbreaks due to these organisms have been associated with the consumption of raw milk or raw milk products. Bulk tank milk (BTM) samples (536) and in-line milk filters (519) collected from dairy farms across the United States during the National Animal Health Monitoring Systems Dairy 2007 study were analyzed by real-time PCR for the presence of S. enterica and pathogenic forms of E. coli and by culture techniques for the presence of L. monocytogenes. S. enterica was detected in samples from 28.1% of the dairy operations, primarily in milk filters. Salmonella was isolated from 36 of 75 PCR-positive BTM samples and 105 of 174 PCR-positive filter samples, and the isolates were serotyped. Cerro, Kentucky, Muenster, Anatum, and Newport were the most common serotypes. L. monocytogenes was isolated from 7.1% of the dairy operations, and the 1/2a complex was the most common serotype, followed by 1/2b and 4b (lineage 1). Shiga toxin genes were detected in enrichments from 15.2% of the BTM samples and from 51.0% of the filters by real-time PCR. In most cases, the cycle threshold values for the PCR indicated that toxigenic strains were not a major part of the enrichment populations. These data confirm those from earlier studies showing significant contamination of BTM by zoonotic bacterial pathogens and that the consumption of raw milk and raw milk products presents a health risk.

Prevalence of Escherichia coli O-Types and Shiga Toxin Genes in Fecal Samples from Feedlot Cattle

While efforts to control foodborne illness associated with the Shiga toxin-producing Escherichia coli (E. coli) O157 through processes and procedures implemented at harvest facilities have been very successful, there is concern about the burden of illness associated with other Shiga toxin-producing E. coli. The U.S. Department of Agriculture Food Safety and Inspection Service announced plans to classify an additional six non-O157 Shiga toxin-producing E. coli as adulterants. Little is known about the prevalence and distribution of these E. coli in the animal production environment. An investigation of the prevalence of O157 and the six major non-O157 E. coli serogroups was conducted in 21 feedlots over the period July 2011 to October 2011. Individual fecal swabs were collected from cattle approximately 60 days after their arrival in the feedlot and were pooled for evaluation using a polymerase chain reaction assay to identify the presence of seven E. coli O-types (O157, O45, O103, O121, O145, O26, and O111) and four virulence genes (stx1, stx2, eaeA, and ehxA). Overall, 1145 fecal pools were evaluated, with 506 (44.2%) being positive for one or more of the E. coli O-serogroups. The pool prevalences for E. coli O157, O45, O26, O103, O121, O145, and O111 were 19.7%, 13.8%, 9.9%, 9.3%, 5.5%, 1.1%, and 0.5%, respectively. Nearly all pools were positive for ehxA (99.7%) or stx2 (98.6%). The pool level prevalence for stx1 and eae was 65.5% and 69.3%, respectively. Pools that were positive for one or more of the other E. coli O-serogroups were 1.37 times more likely to be positive for E. coli O157. Conversely, pools that were positive for E. coli O157 were 1.43 times more likely to be positive for at least one of the other E. coli O-serogroups evaluated. These data will be useful to understand the expected prevalence of potential Shiga toxin-producing E. coli in cattle feedlots.

Associations between housing and management practices and the prevalence of lameness, hock lesions, and thin cows on US dairy operations

The objective of this study was to determine the association among different housing and management practices on the prevalence of lameness, hock lesions, and thin cows on US dairy operations. This study was conducted as part of the National Animal Health Monitoring Systems Dairy 2014 study, which included dairy operations in 17 states. Size categories were assigned as follows: small (30-99 cows), medium (100-499 cows), and large (≥500 cows). Trained assessors visited 191 dairy operations from March through July 2014 and recorded locomotion and hock scores (on a 3-point scale), and the number of thin cows (body condition score ≤2.25) from a total of 22,622 cows (average 118 cows per farm). The majority of cows (90.4%) were considered to be sound (locomotion score = 1), 6.9% were mild/moderately lame (locomotion score = 2), and 2.7% were severely lame (locomotion score = 3). Similarly, most cows (87.3%) had no hock lesions (hock score = 1), 10.1% had mild lesions (hock score = 2), and 2.6% had severe hock lesions (hock score = 3). A low percentage of cows (4.2%) were thin. Univariate comparisons were performed using PROC LOGLINK, which accounts for study design and weighting. Variables meeting the univariate screening criterion of P < 0.20 were eligible for entry into multivariable models. Statistical significance in the multivariable models was declared at P < 0.05. Large operations had a lower within-herd prevalence of cows with locomotion score ≥2 and locomotion score = 3 compared with small or medium-sized operations. Operations on which cows were kept primarily on pasture had a lower percentage of locomotion score = 3 than those housed in freestall or open/dry lot operations. The use of sand bedding was associated with a lower within-herd prevalence of locomotion score ≥2 than straw/hay or dry/composted manure as the primary bedding material. Sand bedding was also associated with a lower within-herd prevalence of locomotion score = 3 than other bedding types except for rubber mats or mattresses. Operations that housed cows in an open/dry lot had a lower percentage of hock score ≥2 and hock score = 3 than other housing types. Providing sprinklers for heat abatement and having a nutritionist balance rations for cows was associated with a lower percentage of thin cows. Results from this study highlight management practices that may reduce the prevalence of lameness, hock lesions, and thin cows on dairy operations in the United States.

Comparison of individual, pooled, and composite fecal sampling methods for detection of Salmonella on U.S. dairy operations.

The objectives of this study were to estimate the prevalence of Salmonella for individual, pooled, and composite fecal samples and to compare culture results from each sample type for determining herd Salmonella infection status and identifying Salmonella serovar(s). During the U.S. Department of Agriculture National Animal Health Monitoring System Dairy 2007 study, data and samples were collected from dairy operations in 17 major dairy states. As part of the study, composite fecal samples (six per operation) were collected from cow areas, such as holding pens, alleyways, and lagoons, where manure accumulates. Fecal samples also were collected from individual cows (35 per operation), and fecal sample pools were created by combining samples from 5 cows (7 per operation). A total of 1,541 composite fecal samples were collected from 260 operations in 17 states, and 406 (26.3%) of these samples were culture positive for Salmonella. Among the 116 operations for which all three sample types were obtained, 41.4% (48 operations) were Salmonella culture positive based on individual samples, 39.7% (46 operations) were positive based on pooled samples, and 49.1% (57 operations) were positive based on composite fecal samples. Relative to individual samples, the sensitivity of composite fecal samples for determining herd infection status was 85.4% and the sensitivity of pooled fecal samples was 91.7%. On 33.6% of operations (39 of 116), Salmonella was cultured from all three fecal sample types (individual, pooled, and composite), and 20 (51.3%) of these operations had exactly the same serovar in all three sample types. Use of composite fecal samples is less costly and time-consuming than use of individual or pooled samples and provides similar results for detecting the presence and identifying serovars of Salmonella in dairy herds. Therefore, composite sampling may be an appropriate alternative to culture of individual samples when assessing Salmonella status in dairy herds.

Farm-Level Associations with the Shedding of Salmonella and Antimicrobial-Resistant Salmonella in U.S. Dairy Cattle

Salmonella enterica is the leading cause of foodborne-related deaths and hospitalizations within the United States. Infections caused by antimicrobial-resistant (AMR) strains are associated with higher hospital costs and case fatality. The objective for this study was to determine the association of management practices with the recovery of Salmonella and AMR Salmonella on dairy herds. Individual adult cow fecal samples and/or composite fecal samples were collected from 265 dairy herds in 17 states. Samples were cultured for Salmonella, and the MIC was determined for 15 antimicrobials. Herds were classified as Salmonella positive if at least one isolate was recovered, and AMR Salmonella positive if at least one resistant isolate was recovered. Questionnaires regarding management practices were administered to herd operators, and a subset of practices was selected based on subject knowledge and prior research. Data on preventive and therapeutic antimicrobial usage were included in the analysis. Logistic regression models were used to determine which practices were significantly (p<0.05) associated with each herd classification. A total of 124 and 25 herds were classified as Salmonella positive and AMR Salmonella positive, respectively. Variables significantly associated with Salmonella-positive herds included using sprinklers or misters for heat abatement (OR=2.8; CI: 1.6-4.9), feeding anionic salts to cows (OR=1.9; CI: 1.1-3.5), and feeding ionophores to cows (OR=2.1; CI: 1.2-3.7). Herds that used a broadcast/solid spread had lower odds (OR=0.26; CI: 0.11-0.63) of being Salmonella positive. Herds with at least one resistant isolate were more likely to have used composted/dried manure for bedding relative to herds with only susceptible isolates (OR=3.6; CI: 1.2-11.0). These results can be useful to focus additional research aimed at decreasing the prevalence of Salmonella and AMR Salmonella on U.S. dairy herds.

A multilaboratory evaluation of a commercial enzyme-linked immunosorbent assay test for the detection of antibodies against Mycobacterium avium subsp. paratuberculosis in cattle.

Five laboratories participated in a study to evaluate sources of variation in results from an enzyme-linked immunosorbent assay (ELISA) for antibodies against Mycobacterium avium subsp. paratuberculosis. Each laboratory repeatedly tested duplicates of a negative, positive (P), and high-positive (HP) serum sample, which were supplied by the United States Department of Agriculture: Animal and Plant Health Inspection Service: Veterinary Services, National Veterinary Services Laboratories, Ames, IA, on all 96-well microtiter plates when routinely testing other samples for M. avium subsp. paratuberculosis antibodies. These 3 sera were aliquoted and sent to the 5 participating laboratories. This study focused on variation in test results because of assay reagents and laboratory techniques and did not account for biologic variability associated with the time course of infection in cattle. Overall, results from 868 microtiter plates were used in the study. For each sample a sample-to-positive (S/P) ratio was calculated according to the manufacturers directions. The S/P ratio for the P sample ranged from 0.06 to 1.039 (mean = 0.466 and 0.484 for wells 1 and 2, respectively) and those for the HP sample ranged from 2.446 to 8.727 (mean = 4.027 and 3.980 for wells 1 and 2, respectively). The majority of the variation in S/P ratio for the P sample was attributed to kit lot (37.5%), followed by random (unexplained) error (27.0%), laboratory (18.3%), and kit lot by laboratory (11.9%). By eliminating plates in which the separation between negative and positive control ODs was less than 0.4, the proportion of variation attributed to laboratory was reduced markedly. These results confirm that there is variability in M. avium subsp. paratuberculosis ELISA results and that several sources contribute to the observed variability. The study gives a relative estimate of the contribution of various sources to the overall variability observed in the M. avium subsp. paratuberculosis ELISA results with kit lot being a primary contributor. Similar data for other ELISA tests for antibodies to M. avium subsp. paratuberculosis or other antigens also should be developed.

Factors affecting use of veterinarians by small-scale food animal operations

OBJECTIVE To identify factors associated with use of a veterinarian by small-scale food animal operations. DESIGN Cross-sectional descriptive survey. SAMPLE 16,000 small-scale farm or ranch operations in all 50 states. PROCEDURES Surveys were conducted via mail or telephone during 2011 for small-scale operations (gross annual agricultural sales between

Estimate of the national incidence of and operation-level risk factors for colic among horses in the United States, spring 1998 to spring 1999

10,000 and

Prevalence of antibodies against Mycobacterium avium subsp paratuberculosis among beef cow-calf herds

499,999) in which an animal or animal product comprised the highest percentage of annual sales. RESULTS 8,186 (51.2%) operations responded to the survey; 7,849 surveys met the inclusion criteria. For 6,511 (83.0%) operations, beef cattle were the primary animal species. An estimated 82.1% of operations (95% confidence interval [CI], 81.1% to 83.0%) had a veterinarian available ≤ 29 miles away; 1.4% (95% CI, 1.2% to 1.7%) did not have a veterinarian available within 100 miles of the operation. Operations for which the nearest veterinarian was ≥ 100 miles away or for which a veterinarian was not available were located in 40 US states. Overall, 61.7% of operations (95% CI, 60.6% to 62.9%) had used a veterinarian during the 12 months prior to the survey. Producers with college degrees were significantly more likely to use a veterinarian (675%) versus those who did not complete high school (52.9%). CONCLUSIONS AND CLINICAL RELEVANCE Results of this study indicated most small-scale operations had adequate access to veterinarians during 2011, but there seemed to be localized shortages of veterinarians in many states.