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A multivalent Bacteroides nodosus foot rot vaccine was tested by comparing the prevalence of foot rot in 317 vaccinated ewes and lambs with the prevalence in 422 unvaccinated control sheep. The vaccine conferred statistically significant protection against foot rot. The vaccine also demonstrated a therapeutic effect in animals with foot rot, after one injection.
A 10% zinc sulfate (ZnSO4) solution was used as a foot bath to control foot rot in pastured lambs. When the foot bath was placed where infected lambs would walk through it each day, clinical evidence of foot rot was greatly reduced within 15 days, and the total number of cases detected after thorough foot trimming was greatly reduced within 30 days. When the foot bath was placed under the salt feeding box, it was not effective. Feeding ZnSO4 at the rate of 0.5 to 0.75 g/head/day was not effective in controlling foot rot. Temperature and moisture conditions were favorable for foot rot transmission throughout the trials.
Sheep affected with foot rot were treated by vaccination and/or hour-long footsoaks, without hoof paring. The response to each treatment was obvious, but the cure rate was not satisfactory for eradication efforts. Booster vaccination and hoof paring combined with medication applied topically greatly improved the response to treatment. There was little difference in response to footsoaking or footbathing when hooves were pared.
A commercial, polyvalent, alum-oil adjuvanted vaccine against foot-rot was tested under conditions where climatic and management circumstances have traditionally made foot-rot difficult to control or eradicate. The vaccine had a protection effectiveness of 84.4% 120 days after the completion of vaccination. Although 93.5% of ewes developed lesions at inoculation sites, they caused no management problems. A negative correlation between foot-rot status and the development of lesions at inoculation sites was considered to show that a sheep factor exists which is related to susceptibility to both foot-rot and reactions at the site of inoculation. The nature of this factor was not determined. Vaccination was considered the easiest and most effective way of controlling the spread of foot-rot among ewes with lambs at foot in the test district.
An 18-week field trial was conducted on a sheep ranch to evaluate the therapeutic and prophylactic effect of a commercial foot rot vaccine. Two hundred sheep were included in the study, 100 with detectable foot rot lesions and 100 without. Approximately 50 sheep from each group were selected randomly and vaccinated twice against foot rot at a 6-week interval in the late spring 1984; the remaining sheep acted as nonvaccinated controls. Therapeutic effect of the vaccine was demonstrated by a cure rate of 53% in vaccinated, foot rot-affected sheep vs a cure rate of 19% in nonvaccinated, foot rot-affected sheep. Prophylactic effect of the vaccine was demonstrated by a foot rot prevalence at the end of the 18-week period of 9% for vaccinated sheep vs 53% for nonvaccinated sheep. Associations of foot rot lesions and vaccination with body condition were found to be significant, as was the association between foot rot lesions and mortality.
Four methods of treatment for ovine foot rot were evaluated: foot trimming and topical treatment (brief, daily foot bathing in 10% zinc sulfate); vaccination with an oil-alum adjuvanted, multivalent, Bacteroides nodosus bacterin, vaccination with the bacterin plus foot trimming and brief foot bathing, and 1-hour 10% zinc sulfate foot soaks. Compared with results of sheep in a nontreated control group, vaccination reduced the number of infected feet by 8%. Daily walk-through foot bathing reduced the number of infected feet by 16%, and vaccination and foot bathing reduced the number by 27%. In another experiment, treated but nonresponsive sheep were subjected to 2 one-hour foot soaks in 10% zinc sulfate. Compared with results in nontreated controls, the soaks reduced the number of affected sheep by 58%. Previously nontreated sheep responded with a 69% reduction of affected animals over controls.
Two decision analysis models were constructed to identify the cost-effectiveness of treatment and/or prevention regimens for ovine foot rot through a systematic evaluation approach of 2 consecutive phases. The first model evaluated the cost-effectiveness of examining the sheep for foot lesions and the use of 1 of 32 treatment regimens when lesions were present. The second model evaluated the 6 most cost-effective treatment regimens from the first model with or without a preventive measure (in this case, vaccination) to determine the most cost-effective approach to preventing/treating foot rot in a single year. Three prevalence levels of foot rot were used. In addition, 3 levels of reduced production attributable to foot rot were used. Threshold analysis, a form of sensitivity analysis, was used to evaluate allowable variations in the success rates and cost of treatments/prevention where the outcome of the models remains unchanged. Of the 32 treatment regimens tested in this model, the use of 10% zinc sulfate applied to the feet of sheep with foot rot was the most cost-effective regimen, regardless of the prevalence levels of the disease or its impact on productivity. In the second model, the use of vaccination with paring of the feet, as a preventive measure, followed by a treatment of the sheep that were still infected, was less cost-effective than to treat only the sheep with foot lesions and disregard prevention. This was true regardless of the prevalence levels of the disease or its impact on productivity.
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)
All cases of foot rot, whether acute, chronic, benign, or inapparent, must be identified. If the outbreak is severe and production losses warrant, each foot of each animal must be examined thoroughly. Proper handling facilities and equipment, adequate light, and dry working conditions are needed to properly examine each foot. Infected sheep must be separated from the clean flock. Following extensive treatment, these animals must be diagnosed as free from the disease before returning to the clean flock. Animals that do not respond must be culled from the flock. Although copper sulfate and formalin are effective materials for footbathing, zinc sulfate is equally effective and does not irritate the skin, eyes, or lungs as does formalin, or stain the wool as does copper sulfate. A 10% zinc sulfate solution with a nonionic surfactant is an effective footbathing or foot soaking solution. The cure rate is improved by a thorough foot paring and a foot soak of at least 30 minutes. A number of treatment options along with formulations are outlined in the 1988 edition of the Sheep Production Handbook of the Sheep Industries Development Program, Inc, 6911 Yosemite, Englewood, CO 80112.
The efficacy of an ethylenediamine dihydriodide containing salt mixture was evaluated with regard to the prevention of naturally occurring foot rot in pastured cattle. Ninety-six cattle were assigned to the treatment group and 96 were assigned to the control group. The groups were allowed consumption of salt-mineral mixtures, ad libitum, that were identical, except with respect to iodine concentration. The control group's mixture contained 0.0025% iodine and the treatment group's mixture contained 0.125% iodine (0.156% ethylenediamine dihydriodide). The incidence of foot rot was measured, as was the severity of the lesions and accompanying lameness. The incidence of foot rot in the control group (20.8%) was significantly (P less than 0.05) greater than the incidence in the treatment group (8.3%). The severity of foot rot was greater (P = 0.024) in the control calves vs the treatment calves. Total serum iodine concentrations were measured in the 2 groups on days 0, 46, and 130 of the experiment. The serum iodine values of the treatment group on day 46 (46 +/- 19.8 g/dl) and day 130 (23 +/- 12.3 g/dl) were significantly different (P less than 0.01) than the serum iodine concentrations of the control animals and the pretreatment values (day 0) of both groups. Production was measured via calf weaning weights. There were no detectable differences between the 205-day adjusted weaning weights of the calves in the control group vs the calves in the treatment group. Clinical signs of iodism were not observed in the cattle involved in this study.
The effects of 3 ovine and one bovine strains of Bacteroides nodosus on the severity of foot-rot, bodyweight and wool growth were compared in Merino sheep in a field experiment. Based on the severity of the induced foot lesions, one strain was classed as virulent (causing underrunning lesions in most feet), one was benign (causing lesions of the interdigital skin only), and 2, including the bovine strain, were of intermediate virulence (causing underrunning lesions in a small proportion of feet). Differences among strains in their effect on foot-rot severity and bodyweight were significant when compared over the whole experimental period, but were not significant at any single time of measurement, because of large differences between replicates. Bodyweight loss and severity of foot-rot caused by the virulent strain were significantly greater than that caused by the benign strain. The intermediate strains lay between these 2 extremes in terms of both bodyweight and foot-rot scores but were not significantly different from either in a statistical sense. Total greasy wool weight did not differ among groups over the whole experiment, but the rate of wool growth during the period when foot lesions were most prevalent and severe was reduced appreciably by the virulent strain and to a lesser extent by the intermediate strains.
Zinc sulfate (ZnSO4) was added to the diet of adult ewes and lambs with contagious foot rot for periods of 4 weeks to 6 months and to the diet of lambs for 5 weeks before experimental exposure to foot rot. Intake averaged between 0.5 and 0.75 g/animal/day. A beneficial effect was demonstrated when lambs with foot rot were fed ZnSO4 and were maintained under dry conditions, but when conditions were wet, ZnSO4 did not reduce the number of infections or prevent new infections. When ZnSO4 was fed before exposure, the infection rate of medicated lambs in a wet environment was almost twice that of unmedicated lambs in the same pen.
Data on incidence of foot rot were collected over 2 years in a mixed herd of both Bos taurus and Bos indicus breed types. The level of infection was significantly higher in the Bos taurus breeds than in the Bos indicus breeds and raises the possibility of using resistant breeds where foot rot constitutes a major economic problem.
Five breeds of sheep, Romney Marsh, Dorset Horn, Border Leicester, Peppin Merinos and Saxon Merinos were examined for their susceptibility to foot-rot by exposure to natural transmission of infection on irrigated pasture or by the application of pure cultures of Bacteroides nodosus to each foot in a pen experiment. On pasture, the sheep encountered a moderate challenge and the British breeds were more resistant than Merinos to the development of severe foot-rot. Resistance was manifested by a rapid resolution of relatively benign lesions in the interdigital skin, rather than a reduction in the number of feet affected. However, under more severe challenges with foot-rot in pens, all breeds were equally susceptible. There was little difference between resistant and susceptible sheep in the kinetics and magnitude of their antibacterial immune responses indicating that resistance did not depend on pre-existing antibody or a more rapid induction of antibody production. In each experiment, humoral immune responses against B. nodosus were not greatly elevated until under-running lesions of the hoof developed.
Twenty holstein heifers were intradermally inoculated in the interdigital skin with a suspension containing Fusobacterium necrophorum and Bacteroides melaninogenicus to induce acute foot rot. Lesions, lameness, and swelling were evaluated during the study, using a subjective scoring system. Rectal temperature, species and number of bacteria isolated, and change in body weight were monitored throughout the study. Ten heifers (treated) were given amoxicillin trihydrate (10 mg/kg of body weight, IM) for 5 days, beginning at the onset of lameness. The remaining 10 heifers (controls) were given physiologic saline solution IM. Treated heifers had less severe lesions and greater weight gain than did control heifers. Rectal temperatures of treated heifers did not differ significantly from those of control heifers. It was concluded that administration of amoxicillin trihydrate early in the course of acute foot rot may reduce the severity of lesions associated with foot rot in cattle.
A novel spirochaete was isolated from a case of severe virulent ovine foot rot (SVOFR) by immunomagnetic separation with beads coated with polyclonal anti-treponemal antisera and prolonged anaerobic broth culture. The as yet unnamed treponeme differs considerably from the only other spirochaete isolated from ovine foot rot as regards morphology, enzymic profile and 16S rDNA sequence. On the basis of 16S rDNA, it was most closely related to another unnamed spirochaete isolated from cases of bovine digital dermatitis in the USA, raising the possibility of cross-species transmission. Further information is required to establish this novel ovine spirochaete as the cause of SVOFR.
Foot rot was experimentally induced in feedlot cattle with a mixed inoculum of Fusobacterium necrophorum (Sphaerophorus necrophus) and Bacteroides melaninogenicus. Both bacteria were isolated from the lesions. Isolates of F necrophorum from 2 of the lesions were serologically compared, using a passive hemagglutination test with the strain used to induce the lesions. These isolates were serologically similar but not identical, indicating antigenic change had occurred during animal passage. The addition of ethylenediamine dihydriodide or urea to the rations did not affect the frequency of experimentally induced foot rot.
Investigations were carried out on the outbreak and spread of foot rot in sheep as well as on the ways of its restriction and eradication. It was found that the disease had been introduced with the import of breeding animals, its further spread being associated with the activity of the Breeding Centers for pedigree animals. The diseased animals have been 25 per cent, on an average, for the whole country, and the economic losses, as expressed in production parameters, have amounted to: produce of animal origin--20 per cent; culling of animals--15 per cent; mortality--1 per cent. Best in the group treatment of the affected animals prove: the dipping in a 5--10 per cent solution of formalin or a 20 per cent solution of copper sulfate, combined with the respective surgical and orthopedic handling and the disinfection of premises. The individual parenteral treatment and the local application of antibiotics and chemotherapeutics have proved suitable and successful in the cases of moderate spread of the disease. The eradication of foot rot can be achieved only via the planned and complex application of pertinent measures.