Social network analysis reveals the failure of between-farm movement restrictions to reduce Salmonella transmission.

An increasing number of countries are investigating options to stop the spread of the emerging zoonotic infection Salmonella Dublin (S. Dublin), which mainly spreads among bovines and with cattle manure. Detailed surveillance and cattle movement data from an 11-yr period in Denmark provided an opportunity to gain new knowledge for mitigation options through a combined social network and simulation modeling approach. The analysis revealed similar network trends for noninfected and infected cattle farms despite stringent cattle movement restrictions imposed on infected farms in the national control program. The strongest predictive factor for farms becoming infected was their cattle movement activities in the previous month, with twice the effect of local transmission. The simulation model indicated an endemic S. Dublin occurrence, with peaks in outbreak probabilities and sizes around observed cattle movement activities. Therefore, pre- and postmovement measures within a 1-mo time window may help reduce S. Dublin spread.

Inter-rater agreement in visual assessment of footpad dermatitis in Danish broiler chickens.

1. The performance of the scoring in the Danish footpad dermatitis (FPD) surveillance system was evaluated by determining inter-rater agreement in visual inspection of FPD in broilers between two independent raters (R1 and R2) and the official scoring at a Danish slaughterhouse. 2. FPD scores were evaluated in 1599 chicken feet. The two raters and the slaughterhouse scored equal proportions of score 0. So did R1 and R2 when assessing score 1 and the more severe lesion score 2, whereas the slaughterhouse scored a markedly higher proportion of score 1 and a lower proportion of score 2. Aggregated FPD flock scores ranged from 5 to 163 (R1 and R2) and from 8 to 107 (slaughterhouse). 3. The level of agreement between the two raters was high for scores 0, 1 and 2 and for flock scores. Agreement between raters and the slaughterhouse was lower when R1 and R2 recorded score 2 than when they recorded scores 0 and 1. 4. This study indicates that the occurrence and severity of lesions are underestimated in the official Danish FPD scoring system.

Serum Amyloid A and Haptoglobin concentrations in calves at first event of respiratory disease were not associated with subsequent risk of respiratory disease during the preweaning period.

Bovine respiratory disease (BRD) causes decreased welfare and production losses and is a major reason for use of antimicrobials in dairy calves. Inflammatory markers released into the blood stream during BRD include acute phase proteins such as Serum Amyloid A (SAA) and Haptoglobin (Hp). This longitudinal observational study aimed to investigate whether the serum concentrations of SAA and Hp measured on the day of a detected mild clinical event of BRD, were associated the odds of developing recurrent BRD events requiring additional treatments in up to a 46-day follow-up period after the first event. A total of 65 preweaned dairy calves were observed for 46 days each in one Danish dairy herd. They were enrolled in this study in the age between 17 and 24 days of age and were followed for the following 46 days in total in which the calves potentially could develop an event of BRD. The calves were clinically assessed every other day using a Visual Analogue Scale (VAS), where a mild BRD event was defined as a calf that deviated from a normal and non-affected calf. The clinical signs included that the calf was less interested in its surroundings, slightly depressed, less bright, alert, and responsive with less clear eyes and using longer time to get up. The calf could have scruffy hair coat and drooping ears. Blood samples were collected on the day of the first mild BRD event that was only treated with a non-steroidal anti-inflammatory drug. A logistic regression model was performed to detect associations between having recurrent events of BRD and VAS, serum SAA and Hp concentrations at the day of the first BRD event and the follow-up period after the BRD event. Only the follow-up period after the first BRD event had a significant association with the odds ratio of having recurrent events of BRD of 2.3 for a 10-day difference in follow-up time after the BRD event.

Salmonella Dublin faecal excretion probabilities in cattle with different temporal antibody profiles in 14 endemically infected dairy herds.

This longitudinal field study investigated the hypothesis that persistently high antibody levels indicate a high risk of Salmonella Dublin shedding in animals in 14 endemically infected dairy herds. A hierarchical multivariable logistic regression was used to analyse 6614 paired faecal cultures and four types of temporal antibody profiles from cattle aged ≥180 days. Age and repeated measurements on animals nested within herds were taken into account. Overall, the prevalence of faecal shedders was low (0·3% and 2·8% in the lowest and highest risk groups, respectively). An important predictor of faecal shedding was young age. There was a significant, but modest increase in risk in cattle with persistently high or recently increased antibody levels, but no difference between these two groups. Contrary to previous recommendations, the detection of carriers by the use of repeated antibody testing is not likely to be a plausible control option in most Salmonella Dublin-infected dairy herds.

Within-herd prevalence of Salmonella Dublin in endemically infected dairy herds.

In this study within-herd prevalence of Salmonella Dublin was investigated in three age groups (calves, young stock, adult cows) during five herd visits at 3-month intervals of 14 endemically infected dairy herds. A total of 10162 paired faecal cultures and antibody measurements were used to calculate the age and temporal dynamics of seroprevalence and prevalence of positive faecal cultures. Faecal culture-positive prevalence was generally low. It was highest (5.4%) in calves during December to February. Seroprevalence varied from 0% to 70% between herds, but was generally more stable in young stock and adult cows than in calves. Hierarchical mixed-model results showed that seroprevalence was associated with the bacteriological status in calves and cows, but not in young stock. These results can be used to develop and validate theoretical infection dynamics models and to design effective control programmes for Salmonella Dublin in dairy herds.

Dynamic changes in antibody levels as an early warning of Salmonella Dublin in bovine dairy herds.

Salmonella Dublin is a bacterium that causes disease and production losses in cattle herds. In Denmark, a surveillance and control program was initiated in 2002 to monitor and reduce the prevalence of Salmonella Dublin. In dairy herds, the surveillance includes herd classification based on bulk tank milk measurements of antibodies directed against Salmonella Dublin at 3-mo intervals. In this study, an "alarm herd" concept, based on the dynamic progression of these repeated measurements, was formulated such that it contains predictive power for Salmonella Dublin herd classification change from "likely free of infection" to "likely infected" in the following quarter of the year, thus warning the farmer 3 mo earlier than the present system. The alarm herd concept was defined through aberrations from a stable development over time of antibody levels. For suitable parameter choices, alarm herd status was a positive predictor for Salmonella Dublin status change in dairy herds, in that alarm herds had a higher risk of changing status in the following quarter compared with nonalarm herds. This was despite the fact that both alarm and nonalarm herds had antibody levels that did not indicate the herds being "likely infected" according to the existing classification system in the present quarter. The alarm herd concept can be used as a new early warning element in the existing surveillance program. Additionally, to improve accuracy of herd classification, the alarm herd concept could be incorporated into a model including other known risk factors for change in herd classification. Furthermore, the model could be extended to other diseases monitored in similar ways.

Evaluation of milk yield losses associated with Salmonella antibodies in bulk tank milk in bovine dairy herds.

The effect of Salmonella on milk production is not well established in cattle. The objective of this study was to investigate whether introduction of Salmonella into dairy cattle herds was associated with reduced milk yield and determine the duration of any such effect. Longitudinal data from 2005 through 2009 were used, with data from 12 mo before until 18 mo after the estimated date of infection. Twenty-eight case herds were selected based on an increase in the level of Salmonella-specific antibodies in bulk-tank milk from <10 corrected optical density percentage (ODC%) to ≥70 ODC% between 2 consecutive three-monthly measurements in the Danish Salmonella surveillance program. All selected case herds were conventional Danish Holstein herds. Control herds (n=40) were selected randomly from Danish Holstein herds with Salmonella antibody levels consistently <10 ODC%. A date of herd infection was randomly allocated to the control herds. Hierarchical mixed effect models with the outcome test-day yield of energy-corrected milk (ECM)/cow were used to investigate daily milk yield before and after the estimated herd infection date for cows in parities 1, 2, and 3+. Control herds were used to evaluate whether the effects in the case herds could be reproduced in herds without Salmonella infection. Herd size, days in milk, somatic cell count, season, and year were included in the models. Yield in first-parity cows was reduced by a mean of 1.4 kg (95% confidence interval: 0.5 to 2.3) of ECM/cow per day from 7 to 15 mo after the estimated herd infection date, compared with that of first-parity cows in the same herds in the 12 mo before the estimated herd infection date. Yield for parity 3+ cows was reduced by a mean of 3.0 kg (95% confidence interval: 1.3 to 4.8) of ECM/cow per day from 7 to 15 mo after herd infection compared with that of parity 3+ cows in the 12 mo before the estimated herd infection. We observed minor differences in yield in second-parity cows before and after herd infection and observed no difference between cows in control herds before and after the simulated infection date. Milk yield decreased significantly in affected herds and the reduction was detectable several months after the increase in bulk tank milk Salmonella antibodies. It took more than 1 yr for milk yield to return to preinfection levels.

Presence of natural genetic resistance in Fraxinus excelsior (Oleraceae) to Chalara fraxinea (Ascomycota): an emerging infectious disease.

Fraxinus excelsior, common ash native to Europe, is threatened by a recently identified pathogenic fungus Chalara fraxinea, which causes extensive damage on ash trees across Europe. In Denmark, most stands are severely affected leaving many trees with dead crowns. However, single trees show notably fewer symptoms. In this study, the impact of the emerging infectious disease on native Danish ash trees is assessed by estimating presence of inherent resistance in natural populations. Disease symptoms were assessed from 2007 to 2009 at two different sites with grafted ramets of 39 selected clones representing native F. excelsior trees. A strong genetic variation in susceptibility to C. fraxinea infections was observed. No genetic or geographic structure can explain the differences, but strong genetic correlations to leaf senescence were observed. The results suggest that a small fraction of trees in the Danish population of ash possess substantial resistance against the damage. Though this fraction is probably too low to avoid population collapse in most natural or managed ash forests, the observed presence of putative resistance against the emerging infectious disease in natural stands is likely to be of evolutionary importance. This provides prospects of future maintenance of the species through natural or artificial selection in favour of remaining healthy individuals.

Modelling food safety and economic consequences of surveillance and control strategies for Salmonella in pigs and pork.

Targets for maximum acceptable levels of Salmonella in pigs and pork are to be decided. A stochastic simulation model accounting for herd and abattoir information was used to evaluate food safety and economic consequences of different surveillance and control strategies, based among others on Danish surveillance data. An epidemiological module simulated the Salmonella carcass prevalence for different scenarios. Cost-effectiveness analysis was used to compare the costs of the different scenarios with their expected effectiveness. Herd interventions were not found sufficient to attain Salmonella carcass prevalence <1%. The cost-effectiveness of abattoir interventions changed with abattoir size. The most cost-effective strategy included the use of steam vacuum and steam ultrasound. Given uncertainty of the effect of steam vacuum and steam ultrasound, model results should be updated as more information becomes available. This framework contributes to informed decision-making for a more cost-effective surveillance and control of Salmonella in pigs and pork.

Prevalence and risk factors for Salmonella in veal calves at Danish cattle abattoirs.

The study's objectives were to determine herd- and animal-level prevalence and herd-level risk factors for Salmonella in dairy-bred veal calves at slaughter in Denmark. In total, 1296 faecal samples were collected at five cattle abattoirs in Denmark during 2007-2008. The animals came from 71 randomly selected specialized veal-calf producers that delivered more than 100 animals to slaughter per year. Salmonella Dublin bacteria were isolated from 19 samples from 12 herds and Salmonella Typhimurium was isolated from one sample. The apparent prevalence of herds delivering Salmonella-shedding animals to slaughter was 18% (95% CI 9-27). The overall estimated true prevalence of shedding calves at slaughter was 1.3%. Veal-calf herds that purchased animals from herds not classified as low risk in the Danish Salmonella surveillance programme had significantly (P=0.03) higher risk of delivering Salmonella-shedding calves to slaughter. The results emphasize the importance of efforts in the dairy industry to ensure food safety for consumers.

Optimal replacement policies for dairy cows based on daily yield measurements.

Markov decision processes (MDP) with finite state and action space have often been used to model sequential decision making over time in dairy herds. However, the length of each stage has been at least 1 mo, resulting in models that do not support decisions on a daily basis. The present paper describes the first step of developing an MDP model that can be integrated into a modern herd management system. A hierarchical MDP was formulated for the dairy cow replacement problem with stage lengths of 1 d. It can be used to assist the farmer in replacement decisions on a daily basis and is based on daily milk yield measurements that are available in modern milking systems. Bayesian updating was used to predict the performance of each cow in the herd and economic decisions were based on the prediction. Moreover, parameters in the model were estimated using data records of the specific herd under consideration. This includes herd-specific lactation curves.

Association between bulk-tank milk Salmonella antibody level and high calf mortality in Danish dairy herds.

Salmonella enterica ssp. enterica Dublin is the most common Salmonella serotype found in the dairy sector in Denmark. Salmonella antibody level in bulk-tank milk (BTM), indicative of Salmonella Dublin infection in the herd, has been recorded regularly in all Danish dairy herds through a surveillance program since 2002. The objective of this study was to investigate whether high BTM Salmonella antibody level was associated with high calf mortality at herd level. Other risk factors for high calf mortality were also investigated: breed, production type (organic vs. conventional), number of animals purchased, herd size, and number of neighbor herds within a 4.9-km radius. Data from the Danish Cattle Database including the Salmonella surveillance program from September 2007 through August 2008 were used. Dairy herds with more than 20 cows were included (n=4,337). Because of a highly right-skewed distribution of calf mortality with many zero values, calf mortality had to be dichotomized for the analysis. Therefore, in this study, high calf mortality was defined as calf mortality of more than 6.5% for calves aged 1 to 180 d. A logistic analysis was performed to identify risk factors associated with the probability of a herd having high calf mortality. The following factors were significantly associated with high calf mortality: high BTM Salmonella antibody level, odds ratio (OR)=2.0 (95% confidence interval=1.6-2.4), organic production OR=1.4 (95% confidence interval=1.1-1.7) for organic versus conventional production, and breed. Purchase of 8 or more animals increased the OR of high calf mortality more than purchase of 1 to 7 animals, which again had a higher OR compared with purchase of 0 animals. Because only 14.3% of the population consisted of herds with high BTM Salmonella status, the estimated proportion of herds with high calf mortality could only be reduced from 38.7 to 36.5% by eradicating Salmonella from the Danish cattle population (i.e., a population attributable risk of 2.2%). This showed that although there is a strong association between BTM Salmonella status and calf mortality, the problem with high calf mortality will not be solved by eradicating Salmonella. All other things equal, a population with more Salmonella-infected herds would gain a larger reduction in calf mortality from a Salmonella control campaign. Nevertheless, individual herds with a high within-herd prevalence of Salmonella are likely to benefit, both economically and regarding animal welfare, from controlling pathogenic Salmonella types in cattle.

The range of influence between cattle herds is of importance for the local spread of Salmonella Dublin in Denmark.

The objective of the study was to estimate the range of influence between cattle herds with positive Salmonella Dublin herd status. Herd status was a binary outcome of high/low antibody levels to Salmonella Dublin in bulk-tank milk and blood samples collected from all cattle herds in Denmark for surveillance purposes. Two methods were used. Initially, a spatial generalised linear mixed model was developed with an exponential correlation function to estimate the range of influence simultaneously with the effect of potential risk factors. An iteratively reweighted generalised least squares procedure was used as a second method for verifying the range of influence estimates. With this iterative procedure, deviance residuals were calculated based on a generalised linear model and the range of influence was estimated based on the residuals using an exponential semivariogram. The range of influence was estimated for six different regions in Denmark using both methods. The analyses were performed on data collected during 1 year after initiation of the Salmonella Dublin surveillance program providing herd classifications for the 4th year-quarter of 2003 and 2 years later for the 4th year-quarter of 2005. The prevalence of dairy herds with a positive Salmonella Dublin herd classification status in this period had decreased from 22.1 to 17.0%. In non-dairy herds, the prevalence was nearly unchanged during the same period (3.4 and 3.7% in 4th quarter of 2003 and 2005, respectively). For all cattle herds, the range of influence was 2.3-6.4 km in 2003 and 1.5-8.3 km in 2005. There seemed to be no association between the range of influence and the density of herds in the different regions.

Acute phase proteins in cattle after exposure to complex stress.

Stressors such as weaning, mixing and transportation have been shown to lead to increased blood concentrations of acute phase proteins (APP), including serum amyloid A (SAA) and haptoglobin, in calves. This study was therefore undertaken to assess whether SAA and haptoglobin levels in blood mirror stress in adult cattle. Six clinically healthy Holstein cows and two Holstein heifers were transported for four to six hours to a research facility, where each animal was housed in solitary tie stalls. Blood samples for evaluation of leukocyte counts and serum SAA and haptoglobin concentrations were obtained before (0-sample) and at 8, 24 and 48 hours after the start of transportation. Upon arrival the animals gave the impression of being anxious, and they appeared to have difficulty coping with isolation and with being tied on the slippery floors of the research stable. Serum concentrations of SAA and haptoglobin increased significantly in response to the stressors (P < 0.01 and 0.05 at 48 hours, respectively). Additionally, the animals had transient neutrophilia at 8 and 24 hours (P < 0.05). In conclusion, the results of the study suggest that SAA and haptoglobin may serve as markers of stress in adult cattle.

Review of transmission routes of 24 infectious diseases preventable by biosecurity measures and comparison of the implementation of these measures in pig herds in six European countries.

This study aimed to review the transmission routes of important infectious pig diseases and to translate these into biosecurity measures preventing or reducing the transmission between and within pig herds. Furthermore, it aimed to identify the level of implementation of these measures in different European countries and discuss the observed variations to identify potentials for improvement. First, a literature review was performed to show which direct and indirect transmission routes of 24 infectious pig diseases can be prevented through different biosecurity measures. Second, a quantitative analysis was performed using the Biocheck.UGent™, a risk-based scoring system to evaluate biosecurity in pig herds, to obtain an insight into the implementation of these biosecurity measures. The database contained farm-specific biosecurity data from 574 pig farms in Belgium, Denmark, France, Germany, the Netherlands and Sweden, entered between January 2014 and January 2016. Third, a qualitative analysis based on a review of literature and other relevant information resources was performed for every subcategory of internal and external biosecurity in the Biocheck.UGent™ questionnaire. The quantitative analysis indicated that at the level of internal, external and overall biosecurity, Denmark had a significantly distinct profile with higher external biosecurity scores and less variation than the rest of the countries. This is likely due to a widely used specific pathogen-free (SPF) system with extensive focus on biosecurity since 1971 in Denmark. However, the observed pattern may also be attributed to differences in data collection methods. The qualitative analysis identified differences in applied policies, legislation, disease status, pig farm density, farming culture and habits between countries that can be used for shaping country-specific biosecurity advice to attain improved prevention and control of important pig diseases in European pig farms.

Risk factors for changing test classification in the Danish surveillance program for Salmonella in dairy herds.

A surveillance program in which all cattle herds in Denmark are classified into Salmonella infection categories has been in place since 2002. Dairy herds were considered test negative and thus most likely free of infection if Salmonella antibody measurements were consistently low in bulk tank milk samples collected every 3 mo. Herds were considered test positive and thus most likely infected if the 4-quarter moving average bulk tank milk antibody concentration was high or if there was a large increase in the most recent measurement compared with the average value from the previous 3 samples. The objective of this study was to evaluate risk factors for changing from test negative to positive, which was indicative of herds becoming infected from one quarter of the year to the next, and risk factors for changing from test positive to negative, which was indicative of herds recovering from infection between 2 consecutive quarters of the year. The Salmonella serotypes in question were Salmonella Dublin or other serotypes that cross-react with the Salmonella Dublin antigen in the ELISA (e.g., some Salmonella Typhimurium types). Two logistic regression models that accounted for repeated measurements at the herd level and controlled for herd size and regional effects were used. Data from 2003 was used for the analyses. A change from test negative to positive occurred in 2.0% of the quarterly observations (n = 21,007) from test negative dairy herds. A change from test positive to negative occurred in 10.0% of quarterly observations (n = 6,168) available from test positive dairy herds. The higher the number of test-positive neighbor herds in the previous year-quarter, the more likely herds were to become test positive for Salmonella. The number of purchased cattle from test-positive herds was also associated with changing from test negative to positive. The bigger the herd, the more likely it was to change from negative to test positive. The effect of herd size on recovery was less clear. Large herds consisting mainly of large breeds or having test-positive neighbors in a 2-km radius were less likely to change from test positive to negative, whereas the breed and neighbor factors were not found to be important for small herds. Organic production was associated with remaining test positive, but not with becoming test positive. The results emphasize the importance of external and internal biosecurity measures to control Salmonella infections.

Evaluation of the Danish footpad lesion surveillance in conventional and organic broilers: Misclassification of scoring.

Danish legislation prescribes surveillance of footpad dermatitis (FPD) at slaughter as an indicator of on-farm broiler welfare. The 3-point scale being used was originally developed in Sweden to score feet from conventional broilers, but the extent and causes of misclassifications have not been investigated, neither in conventional nor organic broilers. Hence, we investigated the performance of the official Danish FPD scoring system in conventional and organic broilers by assessing agreement between official scores from the slaughterhouse and consecutive scoring of the same feet by a reference method. We also investigated the impact of performing an incision of the footpad during scoring. In total, 902 conventional and 897 organic broiler feet (∼100 per flock from 18 flocks) were collected at a large Danish slaughterhouse for the official FPD surveillance system. Laboratory scoring, according to predefined criteria for visual and invasive investigations of the feet derived from the official system, was compared to the official scores assigned at slaughter. Footpad lesions were primarily chronic, representing a wide range of severity. Marked differences in color, shape, and degree of papillary hypertrophy and hyperkeratosis of organic and conventional feet were observed. Low agreement primarily regarding score 2 lesions was observed when comparing official and reference foot scores in conventional (0.31) and organic (0.05) broilers. Variation in agreement when comparing flock scores suggested a non-systematic bias, which might be attributed to differences among official raters. The very low agreement in feet from organic broilers shows that these were more difficult to score than conventional. This might be due to a mismatch between lesion characteristics and scoring criteria, or because the lesions were less severe. Strictly visual examination detected 3 out of 4 score 2 lesions identified by the reference method. This study indicated that a large proportion of severe FPD lesions go unnoticed in the official Danish scoring system. The results further suggested that the complexity and impracticality of the scoring criteria impede uniform scoring among raters and production systems.

Simulation model estimates of test accuracy and predictive values for the Danish Salmonella surveillance program in dairy herds.

The Danish government and cattle industry instituted a Salmonella surveillance program in October 2002 to help reduce Salmonella enterica subsp. enterica serotype Dublin (S. Dublin) infections. All dairy herds are tested by measuring antibodies in bulk tank milk at 3-month intervals. The program is based on a well-established ELISA, but the overall test program accuracy and misclassification was not previously investigated. We developed a model to simulate repeated bulk tank milk antibody measurements for dairy herds conditional on true infection status. The distributions of bulk tank milk antibody measurements for infected and noninfected herds were determined from field study data. Herd infection was defined as having either >or=1 Salmonella culture-positive fecal sample or >or=5% within-herd prevalence based on antibody measurements in serum or milk from individual animals. No distinction was made between Dublin and other Salmonella serotypes which cross-react in the ELISA. The simulation model was used to estimate the accuracy of herd classification for true herd-level prevalence values ranging from 0.02 to 0.5. Test program sensitivity was 0.95 across the range of prevalence values evaluated. Specificity was inversely related to prevalence and ranged from 0.83 to 0.98. For a true herd-level infection prevalence of 15%, the estimate for specificity (Sp) was 0.96. Also at the 15% herd-level prevalence, approximately 99% of herds classified as negative in the program would be truly noninfected and 80% of herds classified as positive would be infected. The predictive values were consistent with the primary goal of the surveillance program which was to have confidence that herds classified negative would be free of Salmonella infection.

Methods and Processes of Developing the Strengthening the Reporting of Observational Studies in Epidemiology-Veterinary (STROBE-Vet) Statement.

Reporting of observational studies in veterinary research presents challenges that often are not addressed in published reporting guidelines. Our objective was to develop an extension of the STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) statement that addresses unique reporting requirements for observational studies in veterinary medicine related to health, production, welfare, and food safety. We conducted a consensus meeting with 17 experts in Mississauga, Canada. Experts completed a premeeting survey about whether items in the STROBE statement should be modified or added to address unique issues related to observational studies in animal species with health, production, welfare, or food safety outcomes. During the meeting, each STROBE item was discussed to determine whether or not rewording was recommended, and whether additions were warranted. Anonymous voting was used to determine consensus. Six items required no modifications or additions. Modifications or additions were made to the STROBE items 1 (title and abstract), 3 (objectives), 5 (setting), 6 (participants), 7 (variables), 8 (data sources and measurement), 9 (bias), 10 (study size), 12 (statistical methods), 13 (participants), 14 (descriptive data), 15 (outcome data), 16 (main results), 17 (other analyses), 19 (limitations), and 22 (funding). The methods and processes used were similar to those used for other extensions of the STROBE statement. The use of this STROBE statement extension should improve reporting of observational studies in veterinary research by recognizing unique features of observational studies involving food-producing and companion animals, products of animal origin, aquaculture, and wildlife.

Explanation and Elaboration Document for the STROBE-Vet Statement: Strengthening the Reporting of Observational Studies in Epidemiology - Veterinary Extension.

The STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) statement was first published in 2007 and again in 2014. The purpose of the original STROBE was to provide guidance for authors, reviewers and editors to improve the comprehensiveness of reporting; however, STROBE has a unique focus on observational studies. Although much of the guidance provided by the original STROBE document is directly applicable, it was deemed useful to map those statements to veterinary concepts, provide veterinary examples and highlight unique aspects of reporting in veterinary observational studies. Here, we present the examples and explanations for the checklist items included in the STROBE-Vet Statement. Thus, this is a companion document to the STROBE-Vet Statement Methods and process document, which describes the checklist and how it was developed.