Distribution and prevalence of footrot in Bhutan

The first cases of footrot in Bhutan were reported in sheep in 1990 at the National Sheep Breeding Centre (NSBC), which supplies breeding animals to village sheep flocks throughout Bhutan. Despite the presence of footrot at the Centre the distribution of apparently disease-free sheep continued. Cases of footrot were reported in village flocks soon after the disease was diagnosed at NSBC. A national survey was designed to establish the distribution and prevalence of footrot in Bhutan. This detected footrot in 19/94 village sheep flocks surveyed. The 19 affected flocks were distributed among nine different administrative districts whereas the villages selected were in 13 of a total of 16 sheep growing districts. The highest within-flock prevalences were among the seven flocks sampled in Bumthang district (mean 20.4%). The prevalence of the disease within flocks was generally much lower in other affected districts and in three districts a single affected animal was identified in the sample of 14 sheep examined in each village. Nationally, footrot prevalence was estimated to be 3.1% (95% CI 2.16-4.04%). There was a positive association between the receipt of animals from NSBC and the presence of footrot. The prevalence of the disease was higher in flocks with a migratory system of management than in those using a sedentary system. The relative risk of there being footrot in a migratory flock was nine-times higher than in a non-migratory flock. Only one strain of Dichelobacter nodosus (serogroup B) was identified among the 234 isolates obtained from the 19 affected flocks. Sheep with footrot healed quickly when treated with a vaccine made from this strain.     

A positive association between resistance to ovine footrot and particular lymphocyte antigen types

The distribution of 12 Class I ovine lymphocyte antigens (OLA) was examined in 4 flocks of sheep vaccinated against and/or challenged with Bacteroides nodosus, the transmitting agent of footrot. In a flock of 47 Corriedales in New Zealand, which had been specially bred for resistance to footrot, a higher frequency (70.2%) of OLA type SY6 was found compared with 42.9% in 49 unselected Corriedale sheep (P = 0.001). The serum antibody response of 12 selected Corriedale ewes was compared with that of 12 unselected ewes of the same age after vaccination with a multivalent footrot vaccine and the selected ewes had significantly (P = 0.01) higher agglutinin titres than the unselected ewes, 7 weeks after vaccination. In 3 trials involving 108, 120 and 135 Australian Merinos in Victoria, SYlb was associated with a reduction in the number of feet affected with severe footrot (P = 0.05, P = 0.01, P = 0.02) and in 2 of the trials there was a relationship between SY6 and high vaccinal agglutinin titres. This SY6 effect was evident in the first trial 31 days after primary vaccination (P = 0.05) and again 20 days later after secondary vaccination (P = 0.01). In the second trial, when the sheep were vaccinated 49 days after challenge, an association was again found between SY6 and high agglutinin titres (P = 0.05) after primary but not after secondary vaccination. Exposure of 157 vaccinated Merino rams to B. nodosus during a footrot outbreak in New South Wales also showed an association between low infection and SY6 and SYlb.(ABSTRACT TRUNCATED AT 250 WORDS)     

Factors affecting the prevalence and severity of footrot in a Merino flock selected for resistance to Haemonchus contortus

SUMMARY An outbreak of virulent footrot occurred in three lines of sheep selected for different levels of resistance to Haemonchus contortus , providing an opportunity to examine the factors affecting footrot severity. The selection lines did not differ significantly in average footrot score, but various other factors were found to have an effect. In breeding ewes, the average score was 10.2 (maximum possible score 20) and the prevalence of footrot was 96%. There was a significant age effect, with average score increasing from 9.1 ± 0.8 in 2-year-old ewes, to 13.4 ± 0.9 in 7-year-old ewes. Ewes that lost their lambs tended to have higher scores than those that either failed to lamb or successfully reared their litter. Significant differences in footrot score were caused by the lambing paddock in which the ewes had been, during the period seven weeks to one week before infection. Among lambs, aged about 20 weeks, the average footrot score was lower (5.0), as was the prevalence (75%). The score increased by an average of 0.09 ± 0.03 per day of age and the prevalence increased by an average of 0.6%± 0.3% per day of age. Lambs born and reared as twins had significantly lower scores than singles, and progeny of maiden dams had lower scores than progeny of older ewes. There was no significant difference because of the sex of the lamb. The paternal half-sib estimate of heritability of footrot score was 0.20 ± 0.14 and of the genetic correlation between footrot score and worm egg count was essentially zero (0.02 ± 0.20), but these estimates were probably biased by the confounding of sires with lambing paddocks. Nevertheless, the results strongly suggest that there are no adverse genetic associations between resistance to footrot and resistance to internal parasites.     

Prevalence of footrot in Swedish slaughter lambs

Background

Footrot is a world-wide contagious disease in sheep and goats. It is an infection of the epidermis of the interdigital skin, and the germinal layers of the horn tissue of the feet. The first case of footrot in Swedish sheep was diagnosed in 2004. Due to difficulties in distinguishing benign footrot from early cases of virulent footrot and because there is no possibility for virulence testing of strains of Dichelobacter nodosus in Sweden, the diagnosis is based of the presence or absence of clinical signs of footrot in sheep flocks. Ever since the first diagnosed case the Swedish Animal Health Service has worked intensively to stop the spread of infection and control the disease at flock level. However, to continue this work effectively it is important to have knowledge about the distribution of the disease both nationally and regionally. Therefore, the aims of this study were to estimate the prevalence of footrot in Swedish lambs at abattoirs and to assess the geographical distribution of the disease.

Methods

A prevalence study on footrot in Swedish lambs was performed by visual examination of 2000 feet from 500 lambs submitted from six slaughter houses. Each foot was scored according to a 0 to 5 scoring system, where feet with score ≥2 were defined as having footrot. Moreover, samples from feet with footrot were examined for Dichelobacter nodosus by culture and PCR.

Results

The prevalence of footrot at the individual sheep level was 5.8%, and Dichelobacter nodosus was found by culture and PCR in 83% and 97% of the samples from feet with footrot, respectively. Some minor differences in geographical distribution of footrot were found in this study.

Conclusions

In a national context, the findings indicate that footrot is fairly common in Swedish slaughter lambs, and should be regarded seriously.     

Effect of climatic region on the clinical expression of footrot of lesser clinical severity (intermediate footrot) in sheep

OBJECTIVE: To determine if the clinical classification of intermediate footrot (IFR) is changed to virulent footrot (VFR) by a transfer of the infected flock to a region where climatic conditions are more favourable for the transmission of the disease. DESIGN: Clinical examination of two groups of Merino wethers infected with IFR; one group of 309 in a region considered less favourable for footrot and another group of 343 at a second site considered more favourable. PROCEDURES: After characterising the form of footrot at the first site, infection was established at the second site by mixing 142 wethers from the first site with 201 unrelated wethers considered to be free of IFR and VFR. Observations of clinical characteristics were made over a 16 month period during which an outbreak of footrot occurred. Clinical assessments were made by inspecting every foot of every sheep at regular intervals and allocating a footscore. Evidence that the same clonal lines of D. nodosus were responsible for the footrot at both sites was provided by serotyping of isolates and using omp gene RFLP as a molecular epidemiological tool. RESULTS: The disease at the first site was classified as IFR because 7% of the sheep developed a maximum footscore (MFS) of 4, the most severe category, despite relatively low rates of transmission. When the outbreak occurred at the second site, which was more suitable for footrot transmission, the maximum proportion of the flock that developed a MFS of 4 was 3.6%, confirming the initial classification of IFR. CONCLUSIONS: When a flock infected with IFR was moved to a region where climatic conditions were more favourable for footrot transmission, the clinical classification of the disease remained the same in both the original flock and in sheep exposed to the infection for the first time.     

Disease resistance in Merino sheep. III. Genetic variation in resistance to footrot following challenge and subsequent vaccination with an homologous rDNA pilus vaccine under both induced and natural conditions

SUMMARY: Eight traits representing clinical indicators of resistance to footrot were examined in 1562 Merino sheep, representing the progeny from 162 sires in four major bloodlines. Over a 4-year period, sheep were exposed to virulent isolates of Dicbelobacter nodosus under both an experimental challenge in which footrot was induced, and a separate natural challenge involving a different isolate of D. nodosus. Five footrot traits and three healing traits were each recorded on seven occasions following induced challenge, and on five occasions following natural challenge. All sheep were vaccinated with a primary and booster injection of an homologous rDNA pilus vaccine, 9 and 6 weeks after initiation of the induced and natural challenge respectively. The major fixed effects which influenced variation in resistance were (in order of importance) time of inspection after challenge, year and group in which sheep were challenged, and sex of the animal. Date of birth, birth-rearing type and age or dam were unimportant in the expression of footrot. Half-sib heritability estimates of resistance to footrot were low to moderate for single observations recorded pre-vaccination (0.07-0.22), and slightly lower for inspections made after vaccination (0.07-0.15). Repeatability estimates for footrot traits during a challenge ranged from 0.31 to 0.70 for inspections pre-vaccination, and 0.19 to 0.35 for inspections post-vaccination. Genetic correlations among footrot traits recorded at repeat inspections were high for observations pre-vaccination (range 0.87-1.00) and slightly lower for observations made after vaccination (0.52-1.00). Heritability estimates derived from repeat measurements approached 0.30 for most traits, except for traits describing healing, which had a heritability of almost zero. Heritability estimates of liability to footrot ranged between 0.09 and 0.41 depending on the time after challenge when the inspections were made. The genetic correlation between induced and natural footrot ranged from 0.14 to 0.95, depending on the period over which inspections were made, with an average of 0.67. In addition to within-flock genetic variation in resistance to footrot, significant differences were observed between different bloodlines within the experimental flock. It was concluded that there is substantial genetic variation in resistance to challenge with virulent isolates of D. nodosus. However, practical restrictions of exploiting available genetic variation may limit the widespread adoption of direct selection. ZUSAMMENFASSUNG: Krankheitsresistenz in Merinos III. Genetische Variabilit?t in Moderhinke Resistenz nach Infektion und folgender Impfung mit homologer rDNA pilus Vakzine unter induzierten und natürlichen Bedingungen Acht Merkmale, die als klinische Hinweise auf Moderhinkeresistenz betrachtet werden, wurden in 1562 Merino Schafen aus 162 Vatertieren von vier wichtigen Linien untersucht. über eine 4-Jahresperiode wurden die Schafe virulenten Isolaten von Dichelobacter nodosus unter Versuchsbedingungen ausgesetzt und eine getrennte natürliche Infektion mit verschiedenen Isolaten von D. nodosus durchgeführt. Fünf Moderhinkemerkmale und drei Gesundungsmerkmale wurden nach Infektion bei sieben Gelegenheiten festgehalten und an fünf nach natürlicher Infektion. Alle Schafe wurden mit einer prim?ren und einer booster Injektion homologer rDNA pilus Vakzine geimpft, 9 und 6 Wochen nach der induzierten und natiirlichen Infektion. Die wichtigsten fixen Effekte, welche die Variabilit?t der Resistenz beeinflussen, waren, nach Wichtigkeit gereint, Zeit der Prüfung nach Impfung, Jahr und Gruppe in welcher Schafe geimpft wurden und Geschlecht. Geburtsdatum, Aufzuchttyp und Mutterschaf-alter waren im Hinblick auf Moderhinke unwichtig. Halbgeschwister-Heritabilit?tssch?tzungen ihrer Resistenz waren niedrig bis mittel für Einzelbeobachtungen vor der Impfung (0,07-0,22) und geringfügig geringer für Beurteilung nach Impfung (0,07-0,15). Wiederholbarkeitssch?tzungen für Moderhinkemerkmale bewegten sich von 0,31 bis 0,70 für Inspektionen vor und 0,19-0,35 für Inspektionen nach Impfung. Genetische Korrelationen zwischen Moderhinkemerkmalen bei verschiedenen Untersuchungen waren fur Beobachtungen vor der Impfung hoch (0,87-1) und geringfügig niedriger nachher (0,52-1). Heritabilit?tssch?tzungen von wiederholten Messungen erreichten 0,30 für die meisten Merkmale au?er für jene, welche Heilung beschreiben, die nahezu keine Heritabilit?t zeigen. Heritabilit?tssch?tzungen für Moderhinkeempfindlichkeit variierten zwischen 0,09 und 0,41 in Abh?ngigkeit von der Untersuchungszeit nach den Impfungen. Die genetische Korrelation zwischen induzierter und natürlicher Moderhinke schwankte von 0,14 bis 0,95 in Abh?ngikeit von der Dauer der Beobachtungsperiode, durschnittlich 0,67. Zus?tzlich zur genetischen Variabilit?t innerhalb der Herde wurden signifikante Unterschiede zwischen verschiedenen Linien innerhalb der Versuchsherde gefunden. Darauf wird es geschlossen, da? substantielle genetische Variabilit?t für Resistenz gegenüber virulenten Isolaten von D. nodosus existiert. Allerdings k?nnen praktische Hindernisse die Ausnutzung der vorhandenen genetischen Variabilit?t durch direkte Selektion einschr?nken.     

An outbreak of rickets in Corriedale sheep: evidence for a genetic aetiology

CASE HISTORY: A skeletal disease characterised by lameness, limb deformities and reduced growth rate occurred over two successive years in lambs born on a commercial sheep farm in Marlborough. A genetic aetiology was considered likely following exclusion of other known causes of rickets and because of the progressive nature of the disease, even after affected animals were transferred to another property. CLINICAL FINDINGS: Affected lambs appeared normal at birth but developed clinical signs during the first 2 months of life. The most severely affected animals either died or were euthanised within the first year of life, but some survived to breeding age. Serum biochemistry revealed hypocalcaemia, hypophosphataemia and increased concentrations of 1,25 dihydroxyvitamin D. The mean serum 25 hydroxyvitamin D concentration was similar to that of control lambs. PATHOLOGICAL FINDINGS: Gross lesions included enlarged costochondral junctions, bilateral irregularity of articular surfaces on humeral heads due to collapse of subchondral bone, thickened cortices in long bones and irregular thickening of physeal cartilages. Microscopically, tongues of hypertrophic chondrocytes extended from physes into metaphyseal regions; metaphyseal trabeculae were thick, disorganised and often lined by wide osteoid seams. Osteoclastic activity was excessive both in cortical and trabecular bone. DIAGNOSIS: Inherited rickets in Corriedale sheep. CLINICAL RELEVANCE AND CONCLUSIONS: This disease is likely to be present in several Corriedale sheep flocks in New Zealand and may have been misdiagnosed as arthritis or other diseases causing lameness and/or poor growth. A defect in end-organ responsiveness to 1,25 dihydroxyvitamin D is the likely mechanism. This disease of sheep may be a useful model for studying vitamin D metabolism and the treatment of inherited forms of rickets in human beings.     

The use of an autogenous Dichelobacter nodosus vaccine to eliminate clinical signs of virulent footrot in a sheep flock in Bhutan

An outbreak of virulent footrot was investigated in a flock of 605 Merino cross-bred sheep in Bhutan. Conventional control methods in the preceding eight years had reduced its prevalence from 36-79% in different components of the flock to about 15% overall. Only one serogroup (B) of Dichelobacter nodosus was identified among 40 isolates cultured from affected sheep. A vaccine prepared from this strain was used in a pilot trial to compare the response of 14 treated and 14 untreated sheep. All affected, vaccinated animals in this trial healed quickly and were protected against re-infection while additional cases developed among untreated sheep during a period favourable for the spread of footrot. The serogroup B vaccine was administered to the whole flock for two successive years. No other footrot treatment was given during these or subsequent years. The whole flock was examined three times, foot by foot, for two years and twice yearly for another two years. When vaccination began there were 88 affected sheep in the flock, an affected sheep being defined as an animal with a foot-score of 2 or greater in one or more feet. There were neither affected sheep in the flock 30 days after the first dose of vaccine nor were any identified in later inspections. Virulent footrot, originating from the farm under investigation, persisted in neighbouring village flocks during this period. It was concluded that whole flock specific D. nodosus vaccination made a major contribution to the elimination of all clinical signs of footrot from the flock of 605 sheep where the condition had previously persisted for 10 years.     

Association between alleles of the ovine major histocompatibility complex and resistance to footrot

Variation in natural resistance to footrot may be genetically derived, implying that genetic markers for resistance may exist and allow selection of superior animals. In this study association between variation within the ovine MHC class II region and resistance to footrot was investigated in two trials. Half-sib progeny were subjected to a field challenge with footrot and their condition subsequently recorded. The animals were then typed at their MHC class II loci to investigate associations between inherited paternal haplotype and footrot status. In the first trial an association between MHC haplotype and footrot status was observed across all animals (P = 0.005), when the self-curing and resistant animals were combined (P = 0.002) and when the self-curing animals were excluded from the analysis (P = 0.001). No association was observed in the second trial, a result attributed to the dry weather conditions which led to poor disease transmission and unreliable disease classification.     

Genetic-associated resistance to foot rot in selected Targhee sheep

Three Targhee rams obtained from the Ohio Agricultural and Experimental Station had been identified as foot rot resistant on the basis of results of challenge exposure. In the first breeding trial, when rams were bred to 20 foot rot-susceptible ewes, the percentages of foot rot-resistant offspring from the 3 foot rot-resistant rams were 68, 82, and 100, compared with 55 and 60 for foot rot-resistant offspring from 2 known foot rot-susceptible rams. In the second year, the foot rot-resistant rams were mated with ewes of unknown foot rot status. The foot rot-resistant status of their lambs was compared with that of range-raised lambs whose parents' foot rot status was unknown. During the first year, challenge exposure to the disease consisted of confinement of the lambs in moist or wet pens with sheep affected with the naturally acquired disease. This protocol was repeated for lambs born during the second-year breeding trial. In addition, the right front foot of each lamb was inoculated with a broth culture of Bacteroides nodosus. During the second year, when data that included infected feet from all lambs were analyzed, 41% of the progeny of the foot rot-resistant rams and 17% of the offspring of parents of unknown foot rot status were unaffected by the disease. When the B nodosus-inoculated foot was not included in the analysis, however, 61% of the progeny of the foot rot-resistant rams and 29% of the others were unaffected. The resistance to foot rot undoubtedly is hereditary. The mechanism of resistance may be in the interdigital skin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Impact of footrot vaccination and antibiotic therapy on footrot and contagious ovine digital dermatitis

Footrot and contagious ovine digital dermatitis (CODD) are common causes of foot disease of sheep in the UK. The study reported here is a split flock randomised treatment trial undertaken on a group of 748 fattening lambs on a UK sheep farm affected by CODD and footrot. The sheep were randomly assigned to one of two treatment protocols. In protocol A, all sheep were given two doses of footrot vaccine (Footvax, MSD), plus targeted antibiotic therapy (long-acting amoxicillin, Betamox LA, Norbrook Pharmaceuticals) to sheep with foot lesions likely to be associated with a bacterial infection. In protocol B, the sheep only received targeted antibiotic therapy. Sheep were re-examined and foot lesions recorded five and nine weeks later. New infection rates in the footrot vaccinated group were lower compared with the vaccinated group for both CODD (18.2 per cent compared with 26.4 per cent, P=0.014) and footrot (12.55 per cent compared with 27.5 per cent, P<0.001). Recovery rates were unaffected for CODD (80.46 per cent compared with 70.97 per cent, P=0.14) but higher for footrot (92.09 per cent compared with 81.54 per cent, P=0.005) in sheep which received the vaccine. On this farm, a footrot vaccine efficacy of 62 per cent was identified against footrot and 32 per cent against CODD infection. An association between a sheep having footrot at visit 1 and subsequently acquiring CODD was identified (odds ratio [OR] 3.83, 95 per cent CI 2.61 to 5.62, P<0.001). These results suggest a role for infection with Dichelobacter nodosus in the aetiopathogenesis of CODD on this farm.     

Transmission of virulent footrot between sheep and goats

OBJECTIVE: To determine the infectivity of ovine and caprine strains of Dichelobacter nodosus for both sheep and goats. DESIGN: Pen experiments in which 20 sheep and 19 goats were challenged directly with the two strains, and transmission experiments on pasture, using donors infected by experimental challenge. RESULTS: Sheep and goat strains of D nodosus infected both animal species in experimental challenges. Animals so infected transmitted footrot to both sheep and goats on pasture plots. A significantly smaller proportion of goats than sheep was infected when challenged with either strain. The interval between exposure and development of footrot in goats was longer than in sheep when recipient animals were exposed to infected donors on pasture. The disease was less invasive in goats than in sheep. CONCLUSIONS: With the strains of D nodosus used there was no evidence of host specificity. Direct transmission of footrot can occur between sheep and goats in the same environment. There is a need to include goats in ovine footrot eradication programs and vice versa.     

Border disease without nervous signs or fleece changes

A natural infection with border disease virus occurred in a flock on low ground in Argyll in the spring of 1984. The outbreak was unusual in that the typical clinical signs of border disease, ie, tremor and, or, fleece changes were not present; manifestations of disease were restricted to abortion and the birth of small weak lambs. The disease was shown to have been introduced to the flock by four healthy ewes persistently infected with border disease virus among a group of 39 purchased in October 1983. Further investigations in late August 1984 detected viraemia in six of seven ill-thriven lambs and four of 24 apparently healthy lambs. Attempted 'natural vaccination' of susceptible sheep by mixing them at grass for three months with groups of ewes and lambs known to contain virus excretors was largely unsuccessful as only four of 22 'sentinel' sheep seroconverted. In October 1984 the persistently infected purchased animals and all that year's lamb crop were removed from the farm. No disease occurred in 1985 when the lambing percentage was 129 per cent compared with 100 per cent in 1984. Two of the four persistently infected purchased ewes were mated at Moredun Research Institute in December 1984 and both produced healthy but persistently infected lambs.     

Factors associated with changes of state of foot conformation and lameness in a flock of sheep

The aim of this research was to investigate transitions between foot conformation, lameness and footrot in sheep. Data came from one lowland flock of approximately 700 ewes studied for 18 months. Multilevel multistate analyses of transitions between good and poor foot conformation states in ewes, and lame and non-lame states in ewes and lambs were conducted. Key results were that the longer sheep had feet in good conformation, the more likely they were to stay in this state; similarly, the longer a ewe was not lame the more likely she was not to become lame. Ewes with poor foot conformation were more likely to become lame (OR: 1.83 (1.24-2.67)) and to be >4 years (OR: 1.50 (1.09-2.05)). Ewes with footrot were less likely to move to good foot conformation (OR: 0.48 (0.31-0.75)) and were more likely to become lame (OR: 3.81 (2.60-5.59)). Ewes lame for >4 days and not treated with parenteral antibacterials had a higher risk of developing (OR: 2.00 (1-3.61)), or remaining in (OR: 0.49 (0.29-0.95)), poor foot conformation compared with ewes never lame. Treatment of ewes lame with footrot with parenteral antibacterials increased the probability of transition from a lame to a non-lame state (OR: 1.46 (1.05-2.02)) and these ewes, even if lame for >4 days, were not more likely to develop poor foot conformation. The risk of a ewe becoming lame increased when at least one of her offspring was lame (OR: 2.03 (1.42-2.92)) and when the prevalence of lameness in the group was ≥5% (OR: 1.42 (1.06-1.92)). Lambs were at increased risk of becoming lame when they were male (OR: 1.42 (1.01-2.01)), single (OR: 1.86 (1.34-2.59)) or had a lame dam or sibling (OR: 3.10 (1.81-5.32)). There were no explanatory variables associated with lambs recovering from lameness. We conclude that poor foot conformation in ewes increases the susceptibility of ewes to become lame and that this can arise from untreated footrot. Treatment of ewes lame with footrot with parenteral antibacterials leads to recovery from lameness and prevents or resolves poor foot conformation which then reduces the susceptibility to further lameness with footrot.     

Observations on the indirect transmission of virulent ovine footrot in sheep yards and its spread in sheep on unimproved pasture

SUMMARY: Virulent ovine footrot was transmitted accidentally to a group of 23 adult Merino sheep (flock B) after holding for 1 hour in sheep yards, which earlier the same day had contained another flock (flock A) with < 1% prevalence of sheep with footrot lesions. Sheep in flock B were rendered susceptible to virulent footrot by grazing 600 mm high unimproved pasture dominated by paspalum ( Paspalum dilatatum ) and kangaroo grass ( Themeda australis ) during warm, humid and wet weather. In addition to moisture, interdigital abrasions caused by the pasture might have predisposed the interdigital skin to infection with Dichelobacter nodosus .     

Benign footrot – an epidemiological investigation into the occurrence, effects on production, response to treatment and influence of environmental factors

SUMMARY Benign footrot was studied in 1 1/2-years-old Merinos on 2 farms in central Victoria from September 1987 to August 1990, Inclusive. Treatment groups of 100 sheep grazed together with the remaining untreated sheep. Inspections were carried out every 3 weeks during the spring transmission period until the number of lesions greater than score 2 dropped below 3%. At each inspection, each sheep was weighed and lesion scores for each foot and digit were recorded, the treated group of sheep was treated by standing in 20% (w/v) zinc sulphate-sodium lauryl sulphate for 1 hour, and bacteriological samples were randomly collected from 5 sheep with and 5 without lesions. Dichelobacter nodosus organisms were obtained from sheep in both groups.
Laboratory tests indicated benign organisms in flock A and low virulence, intermediate organisms in flock B. During the first 2 years, the number and severity of lesions were greater in flock A than in flock B. However, in the third year, with an early 'autumn break', there was a rapid and severe outbreak of footrot in flock B; 98% of the flock had lesions at the first inspection in July 1989. Flock A had a less dramatic increase in lesions of footrot. Both treated and untreated groups in flock B recovered rapidly between the third and fourth inspections. A later increase in lesions for both flocks coincided with damage caused by barley grass seeds. During this period there was a significant difference (P / 0.001) in body weight between the treated and untreated sheep on farm B. An extra 0.2 kg of skirted fleece was obtained from treated sheep when shorn in 1990, compared with the untreated group (P = 0.04). Treated sheep had fewer tender fleeces, 11% compared with 25%. Wool from the untreated group was 0.5 micron finer but the value was 1.79 a head (7%) less than that from the treated group.     

Use of FAMACHA system to evaluate gastrointestinal nematode resistance/resilience in offspring of stud rams

High levels of anthelmintic resistance in gastrointestinal nematodes (GIN) of small ruminants have created the need for animals with greater resistance to these parasites. The objective of this experiment was to evaluate the effectiveness of the FAMACHA system in identification of parasite resilient/resistant offspring, and thus identification of stud rams with greater resilience/resistance. Katahdin ewes bred in separate groups to two sires to lamb in spring (2004, 2005: Ram A and Ram B; 2006, 2007: Ram C and Ram D) at the USDA, Agricultural Research Station in Booneville, Arkansas produced 20-40 offspring/sire each year. Ewes and lambs grazed mixed grass (predominantly bermudagrass and ryegrass) pastures and were supplemented with corn/soybean meal between 30 days pre- and 60 days post-lambing (ewes) and starting 45 days of age until weaning (lambs; 95.0+/-0.6 days of age). Blood samples and feces were collected from the lambs to determine blood packed cell volume (PCV) and fecal egg counts (FEC) and FAMACHA scores were determined at 90, 120, and 150 days of age. Lambs were dewormed if anemic (PCV<19% or FAMACHA score >2) and data removed within 30 days after deworming. Data were analyzed for the 2004/2005 and 2006/2007 groups using general linear models with year, sex of lamb, and sire nested within year as variables. Sire differences were detected (P<0.05 or less) for PCV and FAMACHA at all time points, but not FEC. There tended (P<0.10) to be sire differences for FEC at 90 and 120 days of age, but not at 150 days of age. Lambs sired by Ram D were dewormed less by 150 days of age than those sired by Ram C. The FAMACHA system can be used to identify superior sires for parasite resilience/resistance, thus increasing flock resilience, and perhaps resistance.     

Risk factors associated with the prevalence of footrot in sheep from 1999 to 2000

A postal survey of the techniques being used for the treatment and control of footrot in sheep flocks between November 1999 and October 2000 was conducted in England and Wales in November 2000. Of the 392 questionnaires circulated, 251 (64 per cent) were returned, and 209 of these were usable. Negative binomial regression analysis indicated that the isolation of bought-in sheep, and the separation and individual treatment of diseased sheep with parenteral antibiotics, foot trimming and topical foot sprays were associated with a significantly lower prevalence of footrot in a flock. In contrast, ewe flocks which were routinely foot trimmed more than once a year had a significantly higher prevalence of footrot. No evidence was found that footbathing a flock reduced the level of footrot, except on the 14 per cent of farms where the penning and race facilities for footbathing were reported by the farmer to be excellent. Vaccination had no significant beneficial effect on the level of footrot in a flock     

Looking after the individual to reduce disease in the flock: a binomial mixed effects model investigating the impact of individual sheep management of footrot and interdigital dermatitis in a prospective longitudinal study on one farm

A total of 160 ewes on one farm in England were studied for 18 months. The incidence of footrot and interdigital dermatitis in individually identified sheep and treatment and flock control measures were recorded. A binomial mixed effect model with the incidence of footrot or interdigital dermatitis as the outcome was used to investigate patterns of association between treatments, flock control measures and the incidence of footrot or interdigital dermatitis. In this one flock, the incidence of footrot and interdigital dermatitis was positively associated with the incidence of footrot and interdigital dermatitis and with trimming of feet and negatively associated with the use of parenteral antibiotics and topical antibiotic sprays in either the first and/or second 2-week period prior to the incidence of interest. These results provide two hypotheses: one that 'footrot and interdigital dermatitis are infectious diseases that can be controlled, in part, through the use of antibiotic therapy, which acts to reduce the infectious period of diseased sheep' and two, that 'routine trimming of diseased and healthy feet exacerbate disease, through environmental contamination and/or through increased susceptibility of sheep with recently trimmed feet'.     

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.