Genome-wide association study identifies genetic variants underlying footrot in Portuguese Merino sheep.

BACKGROUND: Ovine footrot caused by Dichelobacter nodosus (D. nodosus) is a contagious disease with serious economic and welfare impacts in sheep production systems worldwide. A better understanding of the host genetic architecture regarding footrot resistance/susceptibility is crucial to develop disease control strategies that efficiently reduce infection and its severity. A genome-wide association study was performed using a customized SNP array (47,779 SNPs in total) to identify genetic variants associated to footrot resistance/susceptibility in two Portuguese native breeds, i.e. Merino Branco and Merino Preto, and a population of crossbred animals. A cohort of 1375 sheep sampled across 17 flocks, located in the Alentejo region (southern Portugal), was included in the analyses. RESULTS: Phenotypes were scored from 0 (healthy) to 5 (severe footrot) based on visual inspection of feet lesions, following the Modified Egerton System. Using a linear mixed model approach, three SNPs located on chromosome 24 reached genome-wide significance after a Bonferroni correction (p < 0.05). Additionally, six genome-wide suggestive SNPs were identified each on chromosomes 2, 4, 7, 8, 9 and 15. The annotation and KEGG pathway analyses showed that these SNPs are located within regions of candidate genes such as the nonsense mediated mRNA decay associated PI3K related kinase (SMG1) (chromosome 24) and the RALY RNA binding protein like (RALYL) (chromosome 9), both involved in immunity, and the heparan sulfate proteoglycan 2 (HSPG2) (chromosome 2) and the Thrombospodin 1 (THBS1) (chromosome 7) implicated in tissue repair and wound healing processes. CONCLUSION: This is the first attempt to identify molecular markers associated with footrot in Portuguese Merino sheep. These findings provide relevant information on a likely genetic association underlying footrot resistance/susceptibility and the potential candidate genes affecting this trait. Genetic selection strategies assisted on the information obtained from this study could enhance Merino sheep-breeding programs, in combination with farm management strategies, for a more effective and sustainable long-term solution for footrot control.

Standardization of loop-mediated isothermal amplification for detection of D. nodosus and F. necrophorum causing footrot in sheep and goats.

The loop-mediated isothermal amplification (LAMP) was standardized for rapid detection of Dichelobacter nodosus and Fusobacterium necrophorum. A total of 250 foot swabs were screened from sheep (200) and goats (50) from different districts of Rayalaseema, viz., Chittoor, Nellore, Kadapa, and Anantapur. Out of 250 samples 75 (30.0%) and 85 (34.0%) were positive for D. nodosus and F. necrophorum, respectively. All the 250 samples were screened individually for both the organisms by LAMP. Among them, 104 (41.6%) were found to be positive for D. nodosus and 120 (48.0%) were positive for F. necrophorum. The efficacy of LAMP in terms of sample DNA detection limit was compared with the PCR by using standard dilutions of DNA extracted from D. nodosus and F. necrophorum cultures. The detection limit was found to be higher than PCR for both the organisms. The sensitivity of LAMP is compared with PCR by targeting 16S rRNA gene of D. nodosus and lktA gene of F. necrophorum. In case of D. nodosus, out of 250 samples, 75 (30.0%) were positive by PCR and 104 (41.6%) were positive by LAMP. Among 250 samples, 85 (34.0%) were positive by PCR and 120 (48.0%) were positive by LAMP in case of F. necrophorum. The LAMP was found to be more sensitive than PCR in detecting the organisms with high statistical significance.

Genomic heterogeneity of Dichelobacter nodosus within and between UK sheep flocks and between age groups within a flock.

BACKGROUND: Footrot and interdigital dermatitis are endemic infectious diseases in all sheep farming regions, impairing welfare and production. The development of efficacious vaccines against the primary causative pathogen has been hampered by the extensive antigenic diversity of Dichelobacter nodosus. Understanding the heterogeneity of the pathogen within and between flocks is essential if the feasibility of bespoke vaccine production is to be assessed for use in the U.K. RESULTS: In this study 56 ewe and lamb isolates from 9 flocks were compared by D. nodosus serogroup and Multi Locus Sequence Type which provides significantly enhanced discriminatory power for molecular epidemiology. Serogroup heterogeneity between flocks ranged from two to five unique serogroups per flock. Three flocks contained isolates of two serogroups, two flocks contained isolates of three serogroups and one flock included isolates of five serogroups. Analysis of 25 isolates from one flock with high prevalence of lameness, identified that serogroup and sequence type was significantly correlated with age. Significantly higher proportion of lambs were infected with serogroup B (principally ST85) as opposed to serogroup H (principally ST86), which predominated amongst adult sheep. CONCLUSIONS: Genomic heterogeneity of the pathogen was significantly lower within flock compared to heterogenicity observed between flocks. Furthermore, this study indicates that within a flock, the host-pathogen dynamics and susceptibility to particular D. nodosus strains may be age dependent.

The prevalence of Dichelobacter nodosus in clinically footrot-free sheep flocks: a comparative field study on elimination strategies.

BACKGROUND: Ovine footrot caused by Dichelobacter nodosus (D nodosus) is an infectious disease affecting sheep worldwide. Switzerland plans a nationwide footrot eradication program, based on PCR-testing of interdigital swab samples. The aim of this study was to test for the presence of D nodosus in clinically footrot-free sheep flocks which had been subjected to different treatment strategies, to assess whether they were feasible for the eradication process, especially focussing on antimicrobial flock treatments. Clinical scoring and PCR-results were compared. Ten farms had used hoof bathing and hoof trimming without causing bleeding, ten had used individual treatments and flock vaccines to gain the free status and ten had become free through whole-flock systemic macrolide treatment. For every farm, three risk-based collected pool samples were analysed for the occurrence of virulent and benign D nodosus by PCR detection of aprV2/aprB2. RESULTS: Six flocks from any treatment group tested positive for aprB2 in all pools. Clinical signs were absent at the time of sampling, but some flocks had experienced non-progressive interdigital inflammation previously. Two flocks tested aprV2-positive in the high-risk pool. One of them underwent a progressive footrot outbreak shortly after sampling. Individual retesting indicated, that virulent D nodosus most likely was reintroduced by a recently purchased ram. In the second flock, a ram was tested positive and treated before clinical signs occurred. CONCLUSIONS: All treatment strategies eliminated the causative agent and were found to be suitable for implementation in the PCR-based eradication process. PCR-testing proved to be more sensitive than visual scoring, as it also detected clinically healthy carriers. It will be of benefit as a diagnostic tool in elimination and surveillance programs.

Prevalence of lameness in sheep transported to meat processing plants in New Zealand and associated risk factors.

Aims: To estimate the prevalence of lameness in sheep transported to meat processing plants in New Zealand, and to identify factors associated with the prevalence of lameness. Methods: The survey was conducted over the main meat processing season, running from October 2012 to the end of May 2013, at 10 sheep processing premises (five North Island and five South Island). A sample of 50 sheep selected from approximately six sheep consignments per week from each of the processing plants were scored for lameness, using a scale from Grade 1 (mild) to 3 (severe, non-weight-bearing). For each consignment the breed, age class and mean carcass weight were recorded. A multivariable regression model was fitted to identify the risk factors for prevalence of lame sheep (Grade 1-3) within a consignment. Results: In total, 1,854/78,833 (2.4 (95% CI = 2.2-2.5)%) sheep were diagnosed with lameness. Of the 1,854 lame sheep, lameness severity was Grade 1 in 1,349 (72.8%), Grade 2 in 450 (24.3%) and Grade 3 in 55 (3.0%) sheep. Within consignments ≥1 lame sheep was observed in 600/1,682 (35.7 (95% CI = 33.4-38.0)%) consignments. In Merino lambs and ewes the prevalence of lameness was greater than that of other breeds (p < 0.001), but in rams/wethers, the prevalence of lameness was lower in Merino than other breeds (p < 0.05). In sheep originating from the North Island, increasing mean carcass weight was associated with an increase in the prevalence of lameness (p < 0.001), but in the South Island prevalence was similar for different carcass weights (p = 0.5). In the North Island increasing yarding time was associated with an increase in the lameness prevalence (p < 0.01), but not in the South Island (p = 0.7). Sheep from the South Island generally had a higher prevalence of lameness than the North Island and the prevalence of lameness was lower over summer and autumn relative to the previous spring (p < 0.01). Conclusion: The results from this survey provided a measure of the prevalence of lameness in a section of the New Zealand sheep population, namely those animals sent for slaughter; as well as identification of several risk factors associated with lameness.

Determination of prevalence, serological diversity, and virulence of Dichelobacter nodosus in ovine footrot with identification of its predominant serotype as a potential vaccine candidate in J&K, India.

The aim of this study was to determine the prevalence, serological diversity, and virulence of Dichelobacter nodosus in footrot lesions of sheep and identification of its predominant serotype as a potential vaccine candidate. The overall prevalence of footrot in sheep was 16.19%, and ranged from 13.69 to 19.71%, respectively. A total of 759 flocks with 22,698 sheep were investigated for footrot and 2374 clinical samples were collected from naturally infected sheep exhibiting footrot lesions. Of the 2374 samples collected, 1446 (60.90%) were positive for D. nodosus by polymerase chain reaction (PCR). These positive samples when subjected to serogroup-specific multiplex PCR, 1337 (92.46%) samples carried serogroup B, 247 (17.08%) possessed serogroup E, 86 (5.94%) serogroup I, and one (0.069%) serogroup G of D. nodosus. While mixed infection of serogroups B and E was detected in 127 (8.78%), B and I in 46 (3.18%) and B, E, and I in 26 (1.79%) samples, respectively. The serogroup B of D. nodosus was the predominant (92.47%) serogroup affecting sheep population with footrot followed by serogroup E (19.91%) and serogroup I (4.57%), respectively. Virulent status of D. nodosus strains were confirmed by presence of virulence-specific integrase A (intA) gene and the production of thermostable proteases. The intA gene was detected in 709 (72.79%) samples while gelatin gel test carried out on 246 representative isolates all positive for intA gene produced thermostable proteases, confirming their virulence nature. The PCR-restriction fragment length polymorphism (PCR-RFLP) of whole fimA gene of serogroup B revealed the predominance of serotype B5 (82.97%) of serogroup B. This information suggests that serotype B5 is the predominant serotype of D. nodosus associated with severe footrot lesions in sheep in Jammu & Kashmir (J&K), India. Hence, this serotype can be a potential vaccine candidate for the effective control and treatment of ovine footrot.

Detection and Serogrouping of Dichelobacter nodosus Infection by Use of Direct PCR from Lesion Swabs To Support Outbreak-Specific Vaccination for Virulent Footrot in Sheep.

Virulent footrot is an economically significant disease in most sheep-rearing countries. The disease can be controlled with vaccine targeting the fimbriae of virulent strains of the essential causative agent, Dichelobacter nodosus However, the bacterium is immunologically heterogeneous, and 10 distinct fimbrial serogroups have been identified. Ideally, in each outbreak the infecting strains would be cultured and serogrouped so that the appropriate serogroup-specific mono- or bivalent vaccine could be administered, because multivalent vaccines lack efficacy due to antigenic competition. If clinical disease expression is suspected to be incomplete, culture-based virulence tests are required to confirm the diagnosis, because control of benign footrot is economically unjustifiable. Both diagnosis and vaccination are conducted at the flock level. The aims of this study were to develop a PCR-based procedure for detecting and serogrouping D. nodosus directly from foot swabs and to determine whether this could be done accurately from the same cultured swab. A total of 269 swabs from the active margins of foot lesions of 261 sheep in 12 Merino sheep flocks in southeastern Australia were evaluated. DNA extracts taken from putative pure cultures of D. nodosus and directly from the swabs were evaluated in PCR assays for the 16S rRNA and fimA genes of D. nodosus Pure cultures were tested also by the slide agglutination test. Direct PCR using extracts from swabs was more sensitive than culture for detecting and serogrouping D. nodosus strains. Using the most sensitive sample collection method of the use of swabs in lysis buffer, D. nodosus was more likely to be detected by PCR in active than in inactive lesions, and in lesions with low levels of fecal contamination, but lesion score was not a significant factor. PCR conducted on extracts from swabs in modified Stuart's transport medium that had already been used to inoculate culture plates had lower sensitivity. Therefore, if culture is required to enable virulence tests to be conducted, it is recommended that duplicate swabs be collected from each foot lesion, one in transport medium for culture and the other in lysis buffer for PCR.

Assessment of a rtPCR for the detection of virulent and benign Dichelobacter nodosus, the causative agent of ovine footrot, in Australia.

BACKGROUND: Ovine footrot is a highly contagious bacterial disease of sheep, costing the Australian sheep industry millions of dollars annually. Dichelobacter nodosus, the causative agent of footrot, is a gram-negative anaerobe classed into virulent and benign strains as determined by thermostability of their respective protesases. Current methods for detection of D. nodosus are difficult and time-consuming, however new molecular techniques capable of rapidly detecting and typing D. nodosus have been reported. RESULTS: A competitive real-time PCR (rtPCR) method, based on the ability to detect a 2 nucleotide difference in the aprV2 (virulent) and aprB2 (benign) extracellular protease gene has been tested on Australian samples for determining detection rates, along with clinically relevant cut-off values and performance in comparison to the traditional culturing methods. The rtPCR assay was found to have a specificity of 98.3% for virulent and 98.7% for benign detection from samples collected. Sheep with clinical signs of footrot showed a detection rate for virulent strains of 81.1% and for benign strains of 18.9%. A cut-off value of a Ct of 35 was found to be the most appropriate for use in Victoria for detection of sheep carrying virulent D. nodosus. CONCLUSIONS: In summary, the rtPCR assay is significantly more capable of detecting D. nodosus than culturing, while there is no significant difference seen in virotyping between the two methods.

The detection and prevalence of leukotoxin gene variant strains of Fusobacterium necrophorum in footrot lesions of sheep in Kashmir, India.

The objective of this study was to determine the prevalence and identification of leukotoxin gene, lktA, variant strains of Fusobacterium necrophorum in the footrot lesions of sheep. The detection of F. necrophorum was carried out by PCR targeting the lktA gene fragment and identification of lktA variant strains was done by PCR-single stranded conformational polymorphism (PCR-SSCP) and gene sequencing. Of the 450 swabs collected from footrot lesions of sheep, 117 were lktA-positive for F. necrophorum. Of the 50 swabs collected from apparently asymptomatic sheep, only one was lktA-positive for F. necrophorum. The overall prevalence of F. necrophorum in footrot affected sheep in Kashmir valley was 26%, and ranged from 20 to 34.8%, respectively. PCR-SSCP of lktA gene fragment analysis revealed three lktA variants, designated as JKS-F1/F2/F3, while two samples (1.7%) showed multiple lktA variant strains of F. necrophorum in a single footrot-affected sheep hoof. This appears to be the first report on the presence of more than one lktA variant of F. necrophorum in a footrot lesion of sheep. The JKS-F3 lktA variant was the most frequent (75.4%), followed by JKS-F2 (14.4%) and JKS-F1 (8.4%), respectively. Among the three lktA variants identified, JKS-F3 was detected in 74 (86.0%) samples from severe footrot affected sheep with a lesion score of 4. The data suggest that JKS-F3 is the predominant lktA variant of F. necrophorum and is associated with severe footrot in sheep. Hence, JKS-F3 may be a significant variant contributing to the severity and duration of the disease in sheep.

Evaluation of Genotypic and Phenotypic Protease Virulence Tests for Dichelobacter nodosus Infection in Sheep.

Dichelobacter nodosus is a fastidious, strictly anaerobic bacterium, an obligate parasite of the ruminant hoof, and the essential causative agent of virulent ovine footrot. The clinical disease results from a complex interplay between the pathogen, the environment, and the host. Sheep flocks diagnosed with virulent but not benign footrot in Australia may be quarantined and required to undergo a compulsory eradication program, with costs met by the farmer. Virulence of D. nodosus at least partially depends on the elaboration of a protease encoded by aprV2 and manifests as elastase activity. Laboratory virulence tests are used to assist diagnosis because clinical differentiation of virulent and benign footrot can be challenging during the early stages of disease or when the disease is not fully expressed due to unfavorable pasture conditions. Using samples collected from foot lesions from 960 sheep from 40 flocks in four different geographic regions, we evaluated the analytical characteristics of qPCR tests for the protease gene alleles aprV2 and aprB2, and compared these with results from phenotypic protease (elastase and gelatin gel) tests. There was a low level of agreement between clinical diagnosis and quantitative PCR (qPCR) test outcomes at both the flock and sample levels and poor agreement between qPCR test outcomes and the results of phenotypic virulence tests. The diagnostic specificity of the qPCR test was low at both the flock and individual swab levels (31.3% and 18.8%, respectively). By contrast, agreement between the elastase test and clinical diagnosis was high at both the flock level (diagnostic sensitivity [DSe], 100%; diagnostic specificity [DSp], 78.6%) and the isolate level (DSe, 69.5%; DSp, 80.5%).

[Performance loss and changes in behaviour caused by footrot]. / Leistungseinbusse und Verhaltensänderung durch Moderhinke beim Schaf.

INTRODUCTION: Two flocks of ewes with lambs were compared for differences in performance. One group was permanently infected with footrot, the other one served as healthy control. They were kept in the same barn but in different bays during lambing and on pasture during the summer. Biweekly all animals were weighed and in the affected group all feet were scored for severity of footrot and if necessary the claws were treated. Furthermore the body condition was scored 4 times in the ewes. The lambs were slaughtered with 43 kg. At that time age and carcass quality were used as parameters. In 20 lambs of each group the lying behaviour was measured using a datalogger during 5 consecutive days. The results revealed significant differences in the performance of ewes and lambs between the two groups. The overall duration of fattening was 31.8 days longer in affected animals. Most importantly, even mild footrot led to significantly impaired growth of the lambs and an altered lying behaviour compared to the healthy controls. The lying periods were more frequent but of shorter duration in affected lambs.

INTRODUCTION: Dans le but d'évaluer la baisse de la performance causée par le piétin chez les moutons, on a comparé deux groupes de brebis avec leurs agneaux, l'un affecté par le piétin et l'autre non. Ces animaux ont tous été détenus dans la même étable dans des enclos séparés et mis au pâturage en été durant toute la journée. Tous les animaux ont été pesés toutes les deux semaines et les onglons ont été évalués et si nécessaire traités dans le groupe présentant du piétin. Chez les brebis, on a estimé à quatre reprises le Body Condition Score. Les agneaux ont été abattus avec un poids moyen de 43 kg, l'âge d'abattage et l'estimation de la carcasse ont été relevés. Dans chaque groupe, 20 agneaux ont été équipés durant 5 jours d'un enregistreur afin de mesurer leur comportement en matière de couchage. Des différences significatives en termes de performances ont été relevées aussi bien chez les brebis que chez les agneaux. La durée d'engraissement était prolongée de 31.8 jours chez les agneaux affectés de piétin. L'information la plus importante est que des signes modérés de piétin conduisent déjà à une baisse significative de la prise de poids des agneaux, mais également à une modification du comportement avec des périodes de couchage plus fréquentes mais moins longues par rapport aux animaux sains.

Identification and characterization of Dichelobacter nodosus serogroup H from ovine footrot in India.

A total of 56 foot swabs were collected from inter digital spaces of sheep with footrot lesions were screened for 16 rRNA of Dichelobacter nodosus by PCR. Out of the 56 samples, 38(67.85%) were found to be positive. All the positive samples were subjected to multiplex PCR targeting fimA gene for identification of serogroups of D. nodosus. Serogroup H was found along with serogroup B in 12 (55.26%) samples and with serogroup I in 8 (22.2%) samples. The serogroup H was identified for the first time from the Indian subcontinent. The phylogenetic analysis of the present sequence with the available serogroup H sequences of GenBank revealed to be in close association with the serotype H1.

Survival of the ovine footrot pathogen Dichelobacter nodosus in different soils.

Dichelobacter nodosus (D. nodosus) is the causative agent of footrot in sheep; one of the most important health and welfare issues of sheep worldwide. For control programmes to be effective, it is essential that the transmission cycle of D. nodosus is understood and bacterial reservoirs in the environment are better defined. This study evaluated the survival of D. nodosus in different soils using soil microcosms. Cultivation independent and dependent methods were used to detect D. nodosus over 40 days from seeding in soil. A D. nodosus specific probe was used for quantification by qPCR and viability was assessed by cell permeability to an intercalating dye, PMA, and by culture. Survival varied dramatically depending on soil type, matric potential (MP) and temperature. Our findings indicate that D. nodosus survival was higher at 5 °C compared with 25 °C in all soils and significantly longer at both temperatures in clay soil (>44% clay) compared with other soil types. Survival under all conditions was longer than 30 days for both culture independent and dependent methods, this is substantially longer than previous studies and, if this is an infectious dose, longer than the current recommendation of resting a field for 14 days to prevent onward infection.

The detection of Dichelobacter nodosus and Fusobacterium necrophorum from ovine footrot in Kashmir, India.

In a study conducted, a total of 450 swab samples from footrot lesions of naturally infected sheep were collected in all the ten districts of the Kashmir valley and were examined for the presence of Dichelobacter nodosus (D. nodosus) and Fusobacterium necrophorum (F. necrophorum), in order to determine if F. necrophorum was associated with ovine footrot. The detection of F. necrophorum and D. nodosus was carried out by polymerase chain reaction targeting the leukotoxin (lktA) and 16S rRNA genes, respectively. In this study, only less than 50% of positive samples contained both the bacteria, so it is not possible to conclude with certainty that both bacteria are together required for the disease manifestation.

Resistance of zebu cattle (Bos indicus) to colonization by major ruminant hoof pathogens.

Zebu cattle (Bos indicus) is reported to be more resistant towards harmful environmental factors than taurine cattle (Bos taurus). A few hundred zebu cattle are kept in Switzerland and in contrast to the Swiss indigenous breeds, infectious hoof disease in zebu is not observed. Therefore, we compared the prevalence of three ruminant hoof pathogens in zebu and taurine cattle. These included Treponema spp., Fusobacterium necrophorum and Dichelobacter nodosus which are associated with bovine digital dermatitis (BDD), different bovine hoof diseases and ovine footrot, respectively. Interdigital swabs and punch biopsies from hind feet of slaughter animals were tested for the three pathogens by PCR. Sixty zebu from eight farms were compared to a convenience sample of 20 taurine cattle from 17 farms. Treponema spp. associated with BDD were not detected in zebu while 23 % of animals and 50 % of farms were positive for benign D. nodosus, with results indicating environmental contamination rather than colonization. Taurine cattle showed 35 % of animals and 41 % of farms positive for T. phagedenis while 90 % of animals and 94 % of farms were colonized by D. nodosus as indicated by a 500-fold higher bacterial load than in zebu. The difference in prevalence of the two pathogens between zebu and taurine cattle was highly significant. F. necrophorum was as well only detected in taurine cattle with values of 15 % of animals and 17.7 % of farms, being significantly different at the animal level. Furthermore, genetic analysis of Swiss zebu indicates high genomic diversity and clear separation from taurine cattle. This is the first evidence that zebu show resistance towards colonization by bacterial hoof pathogens in contrast to taurine cattle.

Molecular Diagnosis of Footrot and Contagious Ovine Digital Dermatitis in Small Ruminants in the Iberian Peninsula.

Contagious ovine digital dermatitis (CODD) and footrot (FR), a sub-acute or acute necrotic (decaying) infectious disease involving the hoof and underlying tissues, pose economic challenges to herds in Spain and worldwide. The aetiological agent for FR is Dichelobacter nodosus, while CODD is caused by pathogenic Treponema phylogroups. We detail the findings derived from the analysis by qPCR of 105 pooled samples from 100 ovine and five caprine herds in Spain and Portugal, alongside 15 samples from healthy flocks in order to identify Dichelobacter nodosus, Fusobacterium necrophorum, Treponema spp., and three pathogenic Treponema phylogroups (T. phagedenis, T. medium, and T. pedis). Treponema spp. were detected in all 120 pools, including samples from the 15 healthy flocks where only one positive result for F. necrophorum was recorded. Mixed infections by agents different from Treponema spp. were identified in 68.57% of samples. Positive results for F. necrophorum and/or D. nodosus, were obtained for 91.4% of the pools, whereas the presence of the three pathogenic Treponema phylogroups was rare: each of them appeared in isolation in a single pool, while they were found in 18 pools in combination with other agents. While F. necrophorum was the sole finding in 16.2% of samples from affected herds, D. nodosus (the footrot causative agent) was only detected in 61% of affected farms. An improved qPCR protocol was implemented to determine the serogroups of D. nodosus in the samples and found all of them (except the G serogroup), often in combined infections (35.1%). This report concludes with comprehensive proposals for diagnosing, preventing, and treating hoof ailments, remarking the interest of the information about D. nodosus serogroups in order to improve the efficiency of immunization by choosing appropriate vaccine protocols.

"I didn't see a sheep": perspectives of lecturers and students at veterinary schools in Great Britain on learning about lameness in sheep.

Introduction: Great Britain has over 15 million ewes. Lameness is one of the top three most economically important diseases for the sheep industry, costing about £80 million per annum. The prevalence of lameness reduced from 10% to 5% between 2004 and 2013 but further reduction is unlikely because many farmers and agricultural students still believe in, and use, ineffective practices to control lameness. Unfortunately, many veterinary practitioners consider themselves insufficiently knowledgeable to work confidently with sheep farmers, and many sheep farmers agree with them. Another route to improve control of lameness is to ensure that all new veterinary graduates are competent to advise farmers. Methods: Our study investigated how veterinary students are taught about management of lameness in sheep. Ten lecturers from eight veterinary schools were interviewed, and 33 students from four veterinary schools participated in four focus groups; all were recorded, transcribed, and analysed using directed qualitative content analysis. Results: Teaching time and opportunities for students to gain clinical experience of lameness were very limited. Students were not confident they could diagnose causes of lameness and listed many practices, including ineffective ones, to manage footrot. Discussion: We conclude that GB veterinary students are graduating without evidence-based understanding and clinical experience necessary to advise farmers on management of lameness in sheep. Given the importance of lameness in sheep in GB we conclude that an alternative approach to education on lameness in sheep could help to ensure that new graduate veterinarians can contribute to control of lameness in sheep.

The virulence of Dichelobacter nodosus, measured by the elastase test, is an important predictor for virulent footrot diagnosis in New South Wales sheep flocks.

Ovine footrot is a contagious bacterial disease that causes foot lesions, and depending on the virulence of the causative strains, may lead to severe underrunning of the hoof and lameness. Virulent footrot can be identified, treated and controlled more effectively than less virulent benign forms. The in vitro elastase test for virulence of the causative bacteria, Dichelobacter nodosus, has been used to support clinical diagnosis. However, not all laboratory-designated virulent D. nodosus strains cause clinical signs of virulent footrot. This study evaluated retrospectively how well the elastase test supported clinical footrot diagnosis in 150 sheep flocks examined for suspect footrot in New South Wales between August 2020 and December 2021. Flocks were included if measures of clinical disease, environmental conditions and the virulence of D. nodosus isolates were available. Variation in the elastase activity result between D. nodosus isolated from the same flock made bacterial virulence hard to interpret, but calculating the mean elastase rate for all isolates from the same flock made correlations between bacterial virulence and flock footrot diagnosis possible. Simplifying bacterial virulence into whether there were any elastase-positive D. nodosus isolates before 12 days increased the predictive value of elastase results for virulent diagnosis, compared with using the first day that any isolate was elastase positive or the percentage of elastase-positive isolates by 12 days, but not all clinically virulent flocks had isolates with elastase activity before 12 days. Logistic regression models were fitted to identify the minimum number of predictors for virulent footrot diagnosis, with models suggesting that virulent footrot diagnosis was best predicted by adding the elastase test result and environmental conditions to the prevalence of severe foot lesions (score 4 and 5). However, performing the same analysis with different breeds, ages of sheep and seasons might highlight other factors important in the diagnosis of virulent footrot.

Erratum: Field validation of a non-carcinogenic and eco-friendly disinfectant in a stand-in footbath for treatment of footrot associated with aprV2-positive strains of Dichelobacter nodosus in Swiss sheep flocks.

[This corrects the article DOI: 10.3389/fvets.2022.812638.].

Network meta-analysis of the therapeutic effects of various antibiotics on footrot in sheep and cattle.

The present network meta-analysis was performed to compare the effects of antibiotics used in treating footrot in some ruminants and to rank these antibiotics based on their efficacy. Data of 14 eligible studies consisting of 5622 affected animals was included in the analysis. A Bayesian method and Markov Chain Monte Carlo (MCMC) simulations were utilized to analyze data. The estimated results were reported in the form of odds ratios (ORs) with 95% credible intervals (CrI). The Surface Under the Cumulative Ranking Curve (SUCRA) was used to rank antibiotics. Network meta-regressions (NMRs) were conducted to examine the influence of sample sizes, treatment duration, route of administration, and species of animals (sheep and cattle) on the overall outcome. The results indicated that gamithromycin impact on curing footrot was superior to other antibiotics and Lincomycin and oxytetracycline were ranked second and third. The difference between the impact of gamithromycin and amoxicillin (OR = 14.76, CrI: 1.07-193.49) and enrofloxacin (OR = 20.21, CrI: 1.57-229.25) on footrot was significant. There was a significant difference between the effect of oxytetracycline and enrofloxacin (OR = 5.24, CrI: 1.14-23.74) on footrot. The NMR performed based on species of animals fitted data better than network meta-analysis, suggesting erythromycin as the best third antibiotic instead of oxytetracycline. Egger's regression test and the shape of the funnel plot showed no publication bias among included studies. In conclusion, gamithromycin was associated with the highest curing rate benefit when used to treat footrot, followed by lincomycin and oxytetracycline/erythromycin. Among all evaluated antibiotics, enrofloxacin showed the lowest effects on footrot.