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.     

Pilot trials in Australia on eradication of footrot by flock specific vaccination

Footrot is a contagious disease of ruminants requiring strains of Dichelobacter nodosus that possess virulence factors including proteases and fimbriae. Sheep can be immunised against footrot using vaccine-containing fimbriae, either native or recombinant. The fimbriae are responsible for the serological K-agglutination reaction, which has been used to classify field isolates into nine major serogroups. The range of protection conferred by vaccination is largely restricted to the serogroup involved, but antigenic competition precludes effective vaccination with multivalent vaccines that contain all serogroups. However, vaccination with specific bivalent recombinant fimbrial vaccine led to eradication of virulent footrot from small ruminants in Nepal and the same result was obtained in Bhutan using a specific whole cell vaccine. In the study reported here two pilot trials have been conducted in Australian sheep flocks, one with a virulent form of footrot caused by a single serogroup F, and the other with an intermediate form also caused by a single serogroup C. In trial 1 pre-vaccination prevalence of clinical footrot in a group of randomly selected animals was 44%. This reduced to 2% at 3 months and 0.5% at 4 months, and there were no clinical cases at 5 months or at 16 months post-vaccination in the whole flock. Similarly in trial 2 pre-vaccination whole flock prevalence was 8.5%, while it was 2% at 3 months, 0.3% at 6 months and zero at 18 months post-vaccination. Use of flock specific monovalent whole cell vaccines over whole flocks for only one season and culling of the few non-responders has been a successful approach in eradication of the disease from both these flocks. This is the first study to report the successful use of specific vaccine for the intermediate form of footrot.     

Broomfield Corriedales: a strain of sheep selectively bred for resistance to footrot

Broomfield Corriedales originate from a 15-year programme of selective breeding from sheep that evaded footrot when deliberately subjected to field challenge. To determine whether this policy may have resulted in improved resistance to footrot, trials were set up in which representative animals from the Broomfield blood-line were challenged with footrot by either experimental or natural infection, together with Corriedale sheep of similar age and sex but from flocks in which the disease is not known to occur. In another approach, the occurrence of footrot was compared in the offspring of Broomfield and of non-Broomfield sires mated with randomly selected ewes in a commercial Corriedale flock in which the condition was prevalent. Finally, the effects of natural challenge in Broomfield lambs were compared with those in a selection line of Corriedale lambs of which both parents had a history of chronic footrot disease. Footrot affected significantly fewer sheep of the Broomfield blood-line and to a markedly lesser degree than those chosen for comparison under identical challenge conditions. Where present, foot infections in Broomfield animals also tended to be less invasive and less persistent. Reduced footrot prevalence was also demonstrated in three birth cohorts of first-cross offspring of Broomfield sires relative to the offspring of other sires, though differences were not significant at all inspections. These findings, considered as a supplement to the historical development of the Broomfield flock, offer encouraging prospects for breeding programmes to enhance the resistance of sheep to footrot disease.     

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 .     

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     

Detection of Oestrus ovis and associated risk factors in sheep from the central region of Yucatan, Mexico

A cross-sectional epidemiologic study was conducted in order to detect the presence of and to estimate the seroprevalence of Oestrus ovis L. infection in flocks of sheep from the central region of the state of Yucatan, Mexico. The risk factors associated with disease were also identified. A sample size of 10 animals per farm was used to detect seropositive animals, considering a 30% prevalence and 95% confidence level. Blood samples of 689 sheep from 88 flocks were collected and a questionnaire with questions about the flock and the host was applied. The thin layer immune assay test was used. The risk factors were screened using logistic regression procedures. 77% of the flocks had at least one-positive animal with antibodies against O. ovis. The overall seroprevalence and standard error was 30.6 +/- 3.5%. Only flock size and sheep nose color showed association (P < 0.05) with the disease. The odds ratios for flocks with less than 11 and with 11 to 25 sheep, as related to herds with 25 or more sheep, were 0.74 and 1.73, respectively. Sheep with dark noses had a higher risk (OR = 1.46) compared with sheep having light noses (P < 0.05).     

Footrot and interdigital dermatitis in sheep: farmers' practices, opinions and attitudes

In 1999, a study was initiated to improve the treatment and control of footrot and interdigital dermatitis in sheep flocks in England and Wales. In November 2000, a retrospective cross-sectional study was conducted in which 392 sheep farmers were asked to estimate the prevalence of footrot and interdigital dermatitis in their flock in the previous 12 months, whether they considered these diseases to be a problem, how they treated and controlled them and their opinion on the success of the treatment and control measures that they used; 209 of them provided usable responses. The farmers tended to be more concerned as the prevalence of the diseases increased; 91 per cent of the farmers with a prevalence of footrot of less than 5 per cent considered it a small or very small problem on their farm, but 51 per cent of the farmers with a prevalence of 5 per cent or more also considered it to be a small or very small problem. Approximately 60 per cent of the farmers who used parenteral antibiotics considered that they were good or excellent at treating footrot, and this treatment was associated with a prevalence of less than 5 per cent. A similar proportion of farmers also considered topical foot sprays and footbathing to be good or excellent for controlling footrot or interdigital dermatitis, but these treatments were not associated with a lower prevalence of footrot or interdigital dermatitis. Of the 29 farmers who used a footrot vaccine, 20 (69 per cent) considered it good to excellent and this was associated with a prevalence of footrot of less than 5 per cent in their flock; however, vaccination was not associated with lower levels of footrot across the whole sample. Farmers spent approximately 34 minutes per sheep per year treating and controlling footrot; 31 per cent were prepared to spend more money and more time to manage footrot, 27 per cent were prepared to spend more time, 19 per cent were prepared to spend more money and 23 per cent were not prepared to do either. The farmers who were willing to invest more money or more money and time had a higher prevalence of footrot.     

Seroepidemiological survey of sheep in Carinthia for the dissemination of ruminant pestiviruses

In this study serological investigations were performed to determine the prevalence of pestiviral infections in sheep in one Federal State of Austria, namely Carinthia. 1527 blood samples from sheep in 147 flocks were collected and tested by Enzyme-linked immunosorbent assay and virus-neutralisation tests for antibodies to ruminant pestiviruses. The estimated flock prevalence was 47.6%, the individual prevalence 16.3%. Significant geographical variations in the flock as well in the individual prevalence were found. The highest prevalence in sheep and in sheep flocks was established in the region Spittal/Drau with 25.9% and 69.7%.The individual and the flock prevalence was significantly higher on farms where cattle or sheep from other farms were present than on farms with no cattle (p < 0.017). All Enzyme-linked immunosorbent assay positive sera were tested for Bovine viral diarrhea virus-1 (strain NADL), Bovine viral diarrhea virus-2 (strain 125) and for Border disease virus (strain MOREDUN) by virus neutralisation tests. Seventy out of 249 positive samples revealed the highest titres (> or = two-fold) to Bovine viral diarrhea virus-1 and 25 to Border disease virus. The remaining positive samples did not show clear results because of cross reactions.     

A longitudinal study of the risks for introduction of severe footrot into sheep flocks in the south west of Norway

In 2008, ovine footrot was detected in Norway for the first time since 1948. By December 2012 it had spread to 99 flocks, all in the county of Rogaland in the south west of Norway, and 42% of which were located in the municipality of Rennesøy in Rogaland. The aim of this study was to investigate risk factors for contracting severe footrot in flocks of sheep. A flock was considered positive for severe footrot based on positive virulence test or by clinical signs in addition to a positive PCR test.     

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.     

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 Parenteral Selenium Administration to Sheep on Prevalence and Recovery from Footrot

Background: Insufficient intake of selenium (Se) is common in many regions, and can contribute to increased susceptibility to and prolonged recovery from infectious diseases. Objective: To determine the effect of Se administration in decreasing the severity and prevalence of footrot in sheep. Animals: Thirty‐eight footrot‐affected and 19 nonaffected sheep from a commercial flock of known high incidence of footrot. Methods: Placebo‐controlled, prospective, 15‐month clinical trial. Footrot‐affected sheep were randomly assigned into 2 groups (n = 19) and injected with either 5 mg Se (footrot [FR]‐Se) or saline (FR‐Sal) at 1‐month intervals for the duration of the study. Unaffected sheep (controls) received no treatment. Sheep feet were examined, trimmed, and scored for footrot with a scale of 0 (no footrot) to 4 (extensive) at 0, 3, 6, 9, and 15 months. Sheep were also bled at time 0 and then at 3, 6, and 15 months to assess whole blood Se concentrations. Results: At time 0, control sheep (255 ± 11 ng/mL) had higher (P < .05) whole blood Se concentrations compared with FR‐Se (205 ± 12 ng/mL) and FR‐Sal (211 ± 14 ng/mL) sheep. By 6 months, FR‐Se sheep (317 ± 9 ng/mL) had whole blood Se concentrations greater (P < .05) than both control (281 ± 14 ng/mL) and FR‐Sal (277 ± 16 ng/mL) sheep. FR‐Se ewes showed a faster decline in highest lesion score at 3 (P= .012) and 6 (P= .0036) months, and a greater decrease in the number of feet with foot score >0 at 6 (P= .020) months compared with FR‐Sal ewes. Sheep with blood Se concentrations <300 ng/mL were at 3.5 times greater risk (1.1–12.1 confidence interval, odds ratio) for FR, although this relationship was only significant (P= .04) at 6 months of the study. Conclusions and Clinical Importance: In sheep with footrot, improved Se status in conjunction with routine control practices result in more rapid improvement of foot lesions.     

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.     

Eradication of virulent footrot from sheep and goats in an endemic area of Nepal and an evaluation of specific vaccination

Programmes based on the identification and treatment of cases and the culling of animals refractory to treatment had failed to eradicate virulent footrot from two districts in the western region of Nepal. From 1993 to 1996 vaccination against two endemic virulent strains of Dichelobacter nodosus was tested for its potential to contribute to the eradication of footrot from the region. Only sheep and goats which had been free of signs of footrot at three inspections at monthly intervals before their annual migration to alpine pastures were eligible for inclusion. From November 1992, the treatment of cases identified during inspections included the injection of specific vaccine. Successfully treated cases migrated with their flocks but were excluded from the vaccine trial. Non-responding cases were culled. Forty combined flocks of sheep and goats (approximately 9500 animals) were used initially to compare three vaccination regimens. Eleven flocks (sheep and goats) were treated with two doses of specific vaccine (group A), nine (sheep and goats) were treated with commercial vaccine followed by specific vaccine (group B) and 10 (sheep and goats) were treated with two doses of commercial vaccine (group C) in March to April 1993 before the annual migration; 10 flocks (sheep and goats) remained unvaccinated (group D). Only sheep and goats free of signs of footrot were allowed to migrate. Nevertheless, virulent footrot recurred in many flocks three months later. However, its prevalence was significantly lower in group A than in the other three groups combined. Groups A, B and C then received the specific vaccine before their migrations in 1994 to 1996; group D remained unvaccinated. The annual programme of inspection and identification and treatment of cases continued for seven years, but the vaccinations ceased after four years. There was no recurrence of virulent footrot after November 1993. After the first season the virulent strains of D nodosus used in the specific vaccine could no longer be isolated, although antigenically distinct, benign strains of the organism persisted in cases of benign footrot.     

Pulmonary adenomatosis (jaagsiekte) of sheep in Canada

Sheep pulmonary adenomatosis has recently been reported in Canada. The literature is briefly reviewed and an account of the present status of the disease in Canada is described.

Sheep pulmonary adenomatosis was first diagnosed in Canada in December 1979 in a first generation descendent of sheep imported from Great Britain. In March 1980 two further cases of sheep pulmonary adenomatosis were diagnosed in a second flock. A total of 43 sheep involving eight flocks from five provinces have been observed from December, 1979 to May, 1981. The clinical signs and laboratory findings were similar to those described in sheep from other countries. It is estimated that 30% of Canadian flocks may contain sheep imported from Great Britain during the 1970's.

     

Outbreak of sheep scab on two adjacent common alpine pastures in the canton of Schwyz (Switzerland)

Sheep scab, which is caused by the mite Psoroptes ovis, is a notifiable disease in Switzerland. In the framework of an epidemiological study in the canton of Schwyz, a sheep scab outbreak on 2 adjacent alpine pastures with 62 flocks (1770 sheep) was followed up clinically, parasitologically and serologically. No mass treatment of the flocks with organophosphates or avermectins had been undertaken before the flocks were taken up to the alpine pastures, but they were treated according to their serological status. Supervised treatment of seropositive judged flocks (at least one seropositive or at least 2 serologically equivocal animals per flock) with Doramectin was undertaken, whilst seronegative judged flocks remained untreated. Sheep returned from the summer pastures in early September 2001 and within three months scab infestation was diagnosed in 53 flocks (85.5%). These infested flocks were scattered all over the canton. Furthermore, the transfer of sheep from 6 infested flocks resulted in the transmission of the disease to 10 new flocks. Infested flocks were kept in quarantine and sanitized. The complexity of the traditional use of shared alpine pastures and the intense, uncontrolled trading with animals render the control of sheep scab difficult.     

Treatment of ovine virulent footrot with zinc sulphate/sodium lauryl sulphate footbathing

Trials were conducted on 2 commercial sheep flocks in the Gippsland region of Victoria to determine the efficacy of treating ovine virulent footrot by footbathing in aqueous zinc sulphate solution (20% w/v). The effects of foot paring, parenteral penicillin, vaccination and addition of sodium lauryl sulphate (SLS) to the footbaths were assessed. Trial 1 comprised 297 sheep with an initial prevalence of footrot of 33% and most lesions were severe and chronic. Treatment of sheep with unpared feet by zinc sulphate footbathing for 1h did not result in a significant reduction in footrot prevalence (n = 120, cure rate 33%) whereas a significant (P less than 0.01) response was obtained by footbathing for 1h with zinc sulphate/SLS (n = 120, cure rate 55%). Trial 2 comprised 1,042 sheep with a pretreatment footrot prevalence of 71% and predominantly severe lesions. In this flock all treated sheep were footbathed in zinc sulphate/SLS for 1h on 2 occasions, 5 days apart and the effects of additional surgical and parenteral treatments were assessed. Foot paring had a significant detrimental effect on cure rate (P less than 0.01). The administration of procaine penicillin at the time of the first footbathing with zinc sulphate/SLS made no significant improvement to the rate of cure. Footrot vaccine given 8 and 2 weeks prior to footbathing did not cure significantly more sheep than footbathing alone, but the results were significantly better than from foot paring plus footbathing, and from combined foot paring, footbathing and parenteral penincillin treatment (P less than 0.01). The cure rate was 84% for sheep that were only footbathed, 72% for those foot pared and footbathed, 72% for those foot pared, footbathed and given penicillin, and 88% for those vaccinated and footbathed.     

Seroprevalence of, and risk factors for, peste des petits ruminants in sheep and goats in Northern Jordan

Peste des petits ruminants (PPR) is an economically important disease that affect sheep and goat industry in Asia and Africa. In this study, we investigated the seroprevalence, and risk factors, of PPR in sheep and goat flocks from five different governorates (Irbid, Jarash, Ajloun, Mafraq and Zarka) located in Northern Jordan. Serum samples from 929 and 400 sheep and goats, respectively, corresponding to 122 sheep flock and 60 goats flock were collected. Seroprevalence was determined using PPR competitive ELISA. Health status and management information were collected using a semi-structured pre-tested questionnaire. The individual true prevalence of PPR in sheep and goats was 29 and 49%, respectively. The flock level true prevalence of PPR was 60 and 74% in sheep and goats, respectively. In both sheep and goat flocks, large flock size, visiting live animals market and inadequate veterinary services were identified as risk factors for PPR seropositivity. Mixed (sheep and goats) raising was identified as a risk factor for PPR seropositivity in sheep flocks only.     

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.     

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.