Efficacy of a novel copper-based footbath preparation for the treatment of ovine footrot during the spread period.

Objective To determine the efficacy of a novel copper based footbath preparation Radicate for treatment of ovine footrot during the spread period.

Design A series of field trials with treated and control groups run together.

Animals Mobs of at least 125 sheep on each of six properties in southern New South Wales with equal numbers of controls.

Procedure Sheep of group A were treated after minimal paring by making them stand in Radicate for 15 minutes. Treatment was undertaken at intervals throughout the period of the trials (14 September to 17 December 1993). Group A sheep were run on the same pasture as those from group B (untreated sheep).

Results The percentage of sheep exhibiting clinical signs of ovine footrot at the start of the trial ranged from 35 to 88% at score 3 or higher, using a 0 to 5 footscoring system. During the trial, the percentage of infected sheep (greater or equal to score 2) in group B increased and ranged from 40 to 90%. The level of infected sheep in group A on each property was reduced progressively to 1 to 16%. Cure rates of 45 to 94% were achieved, with the lowest rate being on a prop- erty with a metal footbath. The next lowest cure rate was 73%. Results indicated that treatment should be undertaken at 2-weekly intervals while spread continues. Treated sheep can be returned to contaminated pastures.

Conclusion Radicate is effective during the spread period and can be used for the progressive eradication of ovine footrot.

Ovine footrot, caused by Dichelobacter nodosus, is the most serious infectious disease of sheep in Australia, causing annual losses of many millions of dollars. In New South Wales alone the disease was estimated to cost the sheep industry $24 million in actual costs in 1988 with the full cost being $48 million (Shepherd 1988). These losses occur through lost wool production, decreased reproduction rates and fertility, loss of body weight and, in extreme cases, death. Losses are also experienced by limiting the access of sheep to markets due to restrictions on the sale of infected sheep and by the social stigma caused to the farm family in some instances. Murnane (1933) and Beveridge (1941) pro- vided details of a number of compounds which had been tried as topical treatments for ovine footrot, either applied individually by brush, or to mobs by means of a footbath. These products included Stockholm tar mixed with bluestone and lysol or ‘Monsol’, picric acid in methylated spirits, sodium arsenite, tartar emetic and lanolin, lactic acid, zinc sulphate, copper sul- phate and formalin. Of these, only zinc sulphate and formalin are currently available in registered formulations. A series of field trials were undertaken during 1993 to 1994 to determine the efficacy of a novel footbath preparation, Radicate, in the treatment of ovine footrot during either the spread or non-spread periods. This paper gives the details of the series of trials conducted during the spread period; those for the non-spread period will be given separately.

Materials and Methods

Trials were conducted during the spring and early summer of 1993, commencing on 14 September 1993, with the final treatment being undertaken on 2 December 1993 and the final clinical assessment on 17 December 1993. A full schedule of the dates of visits to each property is given in Table 1, with treatments corresponding to the dates of each visit.

Trial Sites

Six properties were chosen in the footrot endemic areas of southern New South Wales. Property 1 was at Tumorrama near Tumut, properties 2 and 3 were at Tumblong near Gundagai, property 4 was at Bungowannah near Albury, property 5 was at Goombargana via Walbundrie and property 6 was at Cookardinia near Holbrook. The properties were chosen because of recent histories of infection of the flocks with virulent footrot. They also had footbathing facilities which were considered at the time to be suitable for the trial; four of the properties had concrete footbaths, one had a metal bath which had been painted with a bituminous paint (this was replaced with a fibreglass bath by the end of the trial) and one had metal baths.

Sheep

The aim was to have a minimum of 125 sheep per group (groups A and B) on each property. With the exception of property 2, where the trial mobs were Corriedale-cross ewes, all properties had Merinos. Trial mobs on properties 1 and 6 comprised wethers, property 4 had ewes and properties 3 and 5 had mixed mobs of ewes and wethers. Ages of sheep in the trial ranged from 2 to 6 years. In most instances, the trial mobs comprised the footrot-infected sheep which had been removed previously by the respective property owners from other mobson the property and thus contained sheep with chronic infections. Trial mobs were required to have a minimum level of clinical expression of footrot of 20% of sheep with score 3a or higher (as defined below) at the start of the trial to enable cal- culations of cure rates and to ensure that there was a high level of probability of the presence of highly virulent strains of D nodosus present in the mob.

Measurements Taken

Footscores – All feet of all sheep in the trial mobs were exam- ined at each visit, with lesions of footrot being scored on a scale of 0 to 5 in accordance with the scoring system advocated by the Animal Health Committee’s Working Party on the Coordination of Footrot Control (Stewart and Claxton 1993). An ‘infected’ animal was classified as one with score 2 or higher.

Body weights – Body weights of sheep were recorded on all properties except property l. On the day of the first visit to this property there was heavy rain and the sheep were in 10 to 11 months’ wool. Body weights were therefore considered to be of little value. Body weights were taken on each visit to properties 2, 3 and 6 and at the start and finish of the trial on property 5. On property 4, shearing occurred following the second visit, so body weights were taken pre- and post-shearing as well as at the start and finish of the trial.

Environmental Conditions

Meteorological data were collected for each property during the trial. Assessment of the pasture was also undertaken on each property by visual assessment of the density of the pasture and the major species present.

Laboratory Investigations

Serotyping and virulence testing – Swabs were taken from active footrot lesions from five sheep at the first (properties 1, 2, 4, 5 and 6) or second visit (property 3) to each property, using anaerobic sampling kits supplied by the Regional Veterinary Laboratory (RVL) at Wagga Wagga. These kits con- tained small bottles of Stuart’s transport medium together with 4% hoof agar plates and an agent to convert the contents of the transport jar to anaerobic conditions during transit. The RVL subjected the cultures obtained to serotyping and viru- lence testing, using the elastase and gelatin gel (protease stability) tests (Stewart and Claxton 1993) for the determination of degree of virulence.

Liver copper concentrations – Liver samples from six treated and six untreated sheep from property 4 were submitted to the RVL for analysis of copper levels. Samples were collected 2 and 6 weeks following the initial treatment. The second set of samples were thus taken 4 weeks after the second treatment. The aim was to determine whether there was any justification for more detailed residue studies required for the purposes of product registration.

Histopathology – Histopathological examination was conducted by the RVL Wagga Wagga on feet from the sheep which had been euthanased for the collection of liver samples. The aim was to determine, if possible, the degree of penetration of the formulation, if any, into the tissues of the feet.

Scourability – A sample of the footbath formulation was submitted to the Australian Wool Testing Authority (AWTA) for testing for scourability in accordance with the Australian Wool Scouring Standard, AS 4054-1992.

Footbath stability – Samples of the diluted footbath solution were taken from each property on at least one occasion. Samples were taken following dilution and mixing of the concentrate before any sheep were treated and again at the end of the treatment of the treated group (group A). On property 6, further sampling was undertaken after the fifth visit, when stored diluted footbath was used in association with freshly diluted concentrate. These samples of the diluted footbath solution were returned to the laboratories of the manufacturer for testing for concentration of active constituents and hence the stability of the formulation in its diluted form, as well as checking for any signs of stripping of the active constituents during use.

The Product

Radicate is a patented solution (Australian patent number 653211) of copper II nitrate trihydrate (458 g/L) and copper II chloride dihydrate (80 g/L). It is diluted one part of Radicate to ten parts of water prior to use. It has no detectable odour and mixes readily with water, with minimal agitation required.

Treatment Procedures

The trial mob on each property was randomly divided into two groups. Group A was the treatment group with group B as untreated controls. The two groups were run together for the duration of the trial. Preliminary investigations conducted by the patentor of the product (ML Colburt personal communication), suggested that sheep should be treated on three occasions, with intervals of 2 and 4 weeks between the consecutive treatments. Due to extremely wet and muddy environmental conditions during the trial, leading to high levels of challenge in the trial mobs on each property, this treatment procedure was amended to treatment every 2 weeks for as long as spread continued.
At the time of each visit, as detailed in Table 1, all feet of all sheep in groups A and B were pared to normal conformation, taking care to expose any pockets of infection, or to a degree to allow accurate scoring, whichever was relevant. The degree of paring was less at the second and subsequent inspections. Throughout the trial paring was undertaken in a manner consistent with good welfare of the sheep and thus minimised the possibility of lameness being caused by the act of paring itself.
Following paring, sheep from group A were stood in a solution of Radicate with the footbath being filled to a depth of 45 mm. A flow meter was used to ensure that the mixing rate was accurate. The sheep were stood in the bath for 15 minutes, and observed for any signs of stress or discomfort, any abnormal behaviour or attempts to drink the footbath solution.

 

After treatment the intention was to move them to a clean, dry area, such as concrete, gravel, grating or slats, for at least 15 minutes, after which they were to be moved into the shearing shed or a dry yard for a further hour. It was not possible to achieve these optimal conditions for treatment on all occasions due to weather conditions. On all but one occasion, freshly prepared solution was used for each treatment. On property 6 there was the facility to syphon off and store used footbath solution, after allowing the contaminants to settle. This stored solution was used and topped up with fresh solution on one occasion on this property, as mentioned above.

Sheep Welfare

Paring was undertaken in a manner consistent with good animal welfare. The clinical condition of the sheep was monitored on a daily basis by the farm owner or manager in each instance. Critically affected sheep (those which could not graze properly) in either group were removed from the trial and treated. Where deaths occurred an attempt was made to determine the cause of death.
Calculation of cure and protection rates The cure rate was calculated using the following formula:

Cure rate (percent) = 100-(100 x TSI) / CSI
Where: TSI = number of treated animals originally infected and remained infected. CSI = number of control animals originally infected and remained infected. The protection rate and adjusted protection rate were calculat- ed using the following formulae:

Protection rate (percent) = 100-(100 x TI) / CI
Where: TI = number of treated animals presently infected. CI = number of control animals presently infected.

Adjusted protection rate (percent) = 100-(100 x (TI/CI)l / (TOI/COI)
Where: TI and CI have the same meaning as above. TOI = number of treated animals originally infected COI = number of control animals originally infected. For protection rates to be measured there must be evidence that spread has occurred. For example, if the initial level of infection was 20% the level of infection in a control group would need to reach 30% before the protection rate could be assessed for the chemical under investigation. In this instance the Protection Rate and Adjusted Protection Rate indicate the appropriate time interval between successive treatments during the spread period.

Statistical Analysis

Statistical analysis was undertaken using the x’-test based on the maximum footscores of individual sheep. The ‘maximum footscore’ is the highest footscore for a particular sheep at a particular visit, for example, if a sheep had footscores of 2, 0, 0, 3a, then the maximum footscore for that sheep on that occasion is 3a. The maximum footscore was chosen for the statistical analysis as preliminary statistical assessment based on all footscores showed no greater degree of statistical sensitivity in these trials if all scores were used. Body weights were analysed using one-way analysis of variance.

Environmental Conditions

There was little evidence of spread of footrot (as assessed by the absence of score 2 lesions) on the trial properties when the trial series commenced on 14 September 1993. However, the environmental conditions for the duration of the trial were judged to be highly conducive to the expression and spread of footrot (Graham and Egerton 1968). The rainfall, temperature and pasture conditions throughout the trial, together with an indication as to whether spread was occurring at a particular visit, are summarised in Table 2.

Serology and Virulence

Details of the number of isolates, serotypes and results of virulence testing proved strains classified as ‘virulent’ were therefore confirmed as being present on all properties.

Body Weights

The details of the body weights on properties 2, 4, 5 and 6 are given in Table 4. At the time of the fifth visit the differences in bodyweights and average total weight gain between groups A and B were not significant on property 2, were significant (P < 0.05) with respect to body weight and highly sig- nificant (P < 0.01) with respect to average total weight gain on property 5 and highly significant (P < 0.01) for both body weight and average total gain on properties 4 and 6. The body weight results for property 3 were not considered to be valid, as the trial mob contained pregnant ewes, some of which lambed during the progress of the trial.

Liver Copper Analysis

Analysis of liver copper concentrations demonstrated that there was no increase of liver copper following treatment with Radicate, although no statistical analyses were undertaken on the results. The liver concentration of copper in the untreated animals ranged from 825 pmol/kg to 5338 pmol/kg, while in the treated animals the range was from 690.8 pmol/kg to 1427.4 pmol/kg.

Histopathology

Histopathological examination was carried out on the interdigital skin of the feet of the sampled sheep from property 4. The blue colouring of Radicate did not survive the histopathological processing so degree of penetration of the horn of the feet, if any, could not be assessed, though gross pathology indicated that the product was confined to the superficial layer of the epidermis in the interdigital area. A mild to moderate degree of lymphatic perivascular dermatitis was observed in the interdigital skin. Whether this was due to the action of the chemical or due to infection with D nodosus was not determined. Neither gross nor histopathological examination was undertaken of the horny tissues.

 

Scourability

A sample of Radicate was tested by the AWTA and found to meet the requirements of AS 4054-1992 (High temperature scour). It exhibited a staining scale rating of 4 to 5, where 1 = severe staining and 5 = no staining.

Stability of Footbath Solution

Analysis of the samples of the diluted Radicate collected before and after treatment of sheep and following storage of these samples for one month, confirmed that the product is generally stable in use. This was also the case where used product was stored and re-used at a later date on one occasion on property 6. The one exception was property 1, which had large metal footbaths. On this property, the concentration of active ingredients in the footbath solution as measured after treatment of the last sheep decreased by 14% from the pre- treatment concentration due to electrolytic action as evidenced by the deposition of copper on the metal surface of the footbath. The pre-treatment concentration, taken after the initial mixing of the footbath, was itself 26% below the recommended concentration of Cu” of 13 g/L. This means that there was a 36% reduction in the level of Cu++ overall.

Animal Welfare

Few animals had to be removed from either trial group on any of the properties as a result of severe footrot infection. Extremely favourable pasture conditions allowed animals to graze even with severe footrot. On property 1 several animals had to be removed because of severe balinoposthitis, with deaths attributed to the disease. Two deaths occurred on property 2 due to hypomagnesaemia. No sheep were observed to drink the footbath solution, even when the ambient temperature was in excess of 30′C. Sheep were observed to stand in the footbath without apparent irri- tation From the footbath solution.

Efficancy

The level of clinical expression of the disease in each mob at the start of the trial was considerably higher than the minimum level of more than 20% with a score of 3a or more as required under the trial protocol. From Table 5 it can be seen that the initial clinical expression varied from 36% score 3a or more on property 2, to 88% score 3a or more on property l. The extremely wet and muddy conditions necessitated the use of a water footbath to wash the feet of all sheep prior to examination on most visits on all properties. This made it difficult to accurately determine score 1 lesions on some occasions, but had no apparent adverse effect on the efficacy of the product, as evidenced by the cure rates which were achieved in the presence of such a procedure (Table 5).

Table 2 demonstrates the extreme challenge conditions, which were experienced during the period of the trial on all properties. These conditions, together with the virulence of the strains of D nodosus on the respective properties (Table 3), ensured that spread occurred during the trial period (Table 2). On property 1, it was raining throughout the day of the first inspection and treatment. Sheep were inspected and treated in the rain and had to cross about 10 metres of mud after foot-bathing before entering the shearing shed to allow their feet to dry. These far from ideal treatment conditions experienced on property 1 were contrary to the optimal treatment requirements, as listed under the treatment procedures above, but did not appear to prevent the product from significantly reducing incidence of infection in group A on this property (Table 5).

At the time of the second visit to each property, 2 weeks after the initial visit and treatment, there was a significant drop in the incidence of infection in group A on each property when compared with group B (Table 5). The incidence of infection in group A increased again prior to the third visit on all but property 4, where there was evidently no spread in the intervening 4 weeks. In most cases, this increase in infection was to an incidence higher than that at the commencement of the trial. The incidence of infection in group B likewise continued to increase on all properties with the exception of property 4.

From the time of the fourth visit, which was 2 weeks after the third treatment, the incidence of infection in group A decreased markedly on each property. These differences were all highly significant (P < 0.01) when compared with group B on each property.
The scoring system as used in these trials does not accurately represent the degree of damage being caused by footrot in all instances. For example, following treatment with Radicate, sheep exhibiting a score 5 lesion invariably had a lesion which was restricted to the abaxial wall in the region of the toe. A score 5 lesion in the untreated group was entirely different, with the lesion extending right across the sole and up the abaxial wall with extensive separation.

At the time of the sixth visit, 2 weeks after the fifth treatment, the incidence of infection in group A on each property had been reduced to a range of 1% infected on Property 4 to 16% infected on Property 1 (Table 5).
The cure rates at the time of the fifth visit varied from 45% infected on property 1, to 94% infected on property 4 (Table 5). The results on property 1, while significant, were likely to have been compromised by the reduction of Cu” in the metal footbath due to electrolytic action, as described previously. If property 1 is excluded the range of cure rates is 73 to 94%. Cure rates could not be calculated at the time of the subsequent (sixth) visit as the infected sheep from group B had been treated at the time of the fifth visit to form the trial group for a trial to determine the efficacy of Radicate during the non-spread period. The results of this trial will be reported separately. The infection rates are included to demonstrate that the incidence of infection continued to decrease following treatment at the time of the fifth visit.

The protection rates and adjusted protection rates, together with clinical observations, suggest that a four week treatment interval is inappropriate during the spread period under conditions of severe challenge as experienced during this series of trials (Table 5). These rates suggest that the appropriate treatment interval during the spread period is 2 weeks, which was supported by the clinical assessment.

Discussion

Footbaths, using a variety of chemical agents, have been used in Australia for many years for the control of ovine footrot in mobs of sheep. Murnane (1933) described the use of copper sulphate and formalin, while Beveridge (1941) provided details on the use of these two compounds as well as zinc sulphate, sodium arsenite and a variety of other compounds. As recently as the late 1970s, the authors were aware of sheep farmers in some areas mixing their own ‘brews’ using one or more of these compounds in footbaths.

Regular footbathing in formalin, in association with extensive foot paring, has been used for the control of footrot during the spread period with considerable success (Fitzpatrick 1961; Skerman et al 1983a,b). The use of formalin for this purpose has declined because it is unpleasant to use and there are alternatives such as zinc sulphate footbath products and vaccines available for the control and prevention of spread under favourable conditions. Its efficacy during the spread period is dependent upon paring to uncover all diseased tissue and on treatment at intervals of no more than one week (Fitzpatrick 1961).

In 1983, a formulation containing zinc sulphate plus a wetting agent (sodium lauryl sulphate) was released onto the market. This product (Footrite, Nufarm Animal Health, Australia) does not have the odour and irritancy problems associated with formalin. It has been shown by a number of investigators to be effective in reducing the incidence of footrot in infected flocks (Malecki et al 1983; Atkins 1985). Zinc sulphate alone has also been shown to be highly effective (Demertzis et al 1978; Gradin and Schmitz 1983; Skerman et al 1984). Skerman et al (1983a,b) also demonstrated high efficacy with zinc sulphate whether surfactant was added or not.
Paring prior to treatment with the zinc sulphate and surfactant mixture gave the best results in these trials, but not in others (Malecki and Coffey 1986).

Stewart (1954) discounted the use of copper sulphate for footbathing because of wool staining, the risk of copper poisoning and the reduction of its bactericidal activity in the presence of organic matter. Skerman et al (1984) reported investigations into the efficacy of copper 8-hydroxyquinolate following adverse field efficacy reports in New Zealand. These trials demonstrated that this formulation was ineffective in the treatment of ovine footrot.

Radicate was developed as an effective treatment for use during either the spread or non-spread period, providing an effective alternative to formalin and zinc sulphate formulations in the treatment of ovine footrot (ML Colburt personal communication). The product has no detectable odour and sheep stand in the diluted solution without any signs of irritation. In the trials reported here, Radicate caused no permanent wool staining, although it was observed that splashing could cause temporary discolouration of the wool after treatment. Any discolouration was visually undetectable some 4 to 6 weeks after treatment; repeated treatments did not exacerbate the discolouration. The product was not absorbed via the skin of the feet to a detectable extent, as confirmed by the liver copper levels and the gross pathological examination of feet from treated sheep; as a result, it is concluded that residues in edible tissues would not result from the use of the product.
No sheep were observed to drink the footbath solution, even when the ambient temperature was in excess of 30′C. The risk of copper poisoning is thus considered minimal. Sheep were also observed to stand in the footbath without any apparent signs of irritation from the footbath solution.

In contrast to the findings of Stewart (1954) with copper sulphate, these trials showed Radicate to be highly effective in the treatment of ovine footrot during the spread period when used with the appropriate management. These results were not compromised by the presence of organic matter in the footbath, as occurs in the case of copper sulphate (Stewart 1954). Nonetheless, it is regarded as good practice to ensure that the sheep’s feet are clean of mud prior to entering the footbath to ensure maximum penetration of the formulation into the diseased tissues of the infected feet. Due to muddy conditions which prevailed during the trials, it was necessary on the majority of occasions, to wash the sheep’s feet in troughs of water prior to examination in order to facilitate accurate footscoring. While this made it more difficult to be accurate on all score 1 lesions, it had the advantage of making it easier to identif’y other lesions and ensured that all feet were clean prior to treatment. This procedure did not appear to compromise the efficacy of the product, as demonstrated by the significant reduction in incidence and high cure rates on all properties (Table 5). On the one property on which there was a lesser reduction in incidence (property 1), the performance was compromised by the use of metal baths, as stated above, and not by washing of the feet before the examination.

Use of the product during the spread period is likely to mean that in some instances the ideal conditions for treatment will not be achieved. Even so, these trials show that the product will significantly reduce the level of infection in infected flocks (Table 5).

The results are given in terms of infected sheep as this is the relevant level of assessment as used by sheep growers and is also the most appropriate level of assessment to satisfy the regulatory requirements For such a product.

As stated previously, a deficiency of the scoring system used in these trials is that it does not accurately represent the degree of damage in all instances. A score 5 lesion which was restricted to the abaxial wall in the region of the toe, as was common following treatment with Radicate, would have far less impact on productivity than a lesion extending right across the sole and up the abaxial wall with extensive separation, as was common in those sheep with score 5 which had not been treated. While it can be argued that these differences are irrclevant in the final analysis, we believe that they are significant in assessing responses to treatment during the spread period and are reflected in the differences in body weights between the two groups on most properties.

Sheep from group A were required to stand on dry concretc for at least 15 minutes prior to being moved onto slats in the shearing shed, or some other dry area. This procedurc was not followed with group B. While it could be argued that this difference could account for the reduction in infection rate in favour of group A, such an argument is not valid in view of thc large differences in incidence betwcen the two groups. Also, during the early stages of development of the product it was found that, although Radicate gave good results if sheep were allowed to go from the footbath onto wet or muddy yards or paddocks, the reduction in incidence was much greater if a drying time was included (ML Colburt personal communication). This was reinforced by the results on property I (Table 5) where sheep had to pass through about 10 metres of mud after footbathing and prior to entering the shearing shed. The incidence was reduced from 91% to 65% for group A and 91 to 86% for group B.

The high cure rates were thus achieved on all properties in the face of severe challenge from group B, where the incidencc of infection at score 3a or greater exceeded 90% on one or more occasions during the trial.
This series of trials effectively finished at the time of the fifth visit to each property. In most instances there was little or no evidence of spread at this stage. However, on property 1, where spread was still occurring, the condition and incidence oF infection of the sheep in group B was such that it was decided to treat all infected sheep on welfare grounds. Termination of the trials at this stage and subsequent use of infected sheep from group B for a series of trials to determine the efficacy of Radicate during the non-spread period (to be reported separately), meant that the cure rate could not be calculated at visit 6. The figures for the incidence on the respective proper- ties are included to demonstrate that the incidence in group A on each property continued to decline after the fifth treat- ment. It is still valid to consider this set of figures as transmis- sion was no longer occurring on most of the properties, as evidenced by lack of score 1 and score 2 lesions.

It should also be noted that the interval between the second and third visits was four weeks. It became evident that this interval was too great, particularly under the conditions of severe challenge as experienced during these trials, as the incidence of infection in group A increased during this period on all properties except property 4, where spread had not occurred in the intervening period (Tables 2 and 5). Returning to 2-week intervals brought rapid and significant reductions in the incidence of infection. Clinical examination of the newer lesions at the time of the third visit indicated that the product was unable to provide protection beyond 2 to 3 weeks after treatment during the spread period. The protection rates and adjusted protection rates, together with the clinical observations, suggest that a 2-week interval between consecutive treatments is appropriate during the spread period (Table 5).

During the trial, sheep were inspected every two weeks at the time of each visit. Cure rates were assessed on the results achieved at the visits from visit 2 on each property, with the timing being dictated by the residual protection offered by the product. The cure rates as determined at the end of the trial can only be validated by further inspections during the drier (non-transmission) period over the summer months. One cannot be confident of cure unless there are at least two inspections at intervals of at least four weeks following the final treatment. This recommendation is included under ‘Directions for use’ of the product on its registered label.
The protocols for the testing of products for the treatment and/or control of ovine footrot require an untreated control group throughout the period of the trial. While not questioning the scientific justification for such a requirement, this can place a severe challenge on any product, particularly if the degree of infection in the control group is high (above 50%), as in this trial. It is certainly not consistent with the manner in which a product would be used on a commercial property, where all sheep (or at least all infected sheep) in any one mob would be treated. The results achieved for the Radicate treatment regime in this trial could therefore be regarded as conservative, especially in view of the high, or even extreme, level of challenge experienced in this series of trials.

Two perceived disadvantages of the product from the farmer’s point of view are the temporary discolouration of the wool from splashing and the corrosion of metal caused by the copper salts. The discolouration is scourable, as indicated above. With respect to the corrosion, it is recommended that the product be used in footbaths constructed from concrete, fibre glass or plastic; it should not be used in metal footbaths unless they have been correctly treated with some sort of protective coating, such as bituminous paint. This last type was used in the initial stages of the trial on property 5 without any reduction in the level of active constituents. Any metal rails around footbaths should be protected by timber or by rubber belting to minimise the possibility of corrosion. These methods also reduce the degree of splashing and thus the degree of wastage of the product and are useful no matter what materials are used for rails around the footbaths.

The conditions under which the series of trials were run, together with the results, also demonstrate a distinct managerial advantage offered for this product in that sheep treated with Radicate can be returned to contaminated pasture without increasing the disease risk. This allows the farmer a high degree of flexibility in the management of stock during the spread period.

In examining treated feet, it was clearly observed that Radicate had penetrated vertically along the laminae which were damaged by footrot. While there is no evidence available for lateral penetration of the horn tissue of the feet, this vertical penetration of the diseased tissues is undoubtedly relevant to the overall performance of the product.

These trials have confirmed that Radicate is an effective product for the treatment of ovine footrot during the spread period when used in association with appropriate management practices. It has the advantage of offering sufficient residual efficacy to allow infected sheep to be returned to contaminated pasture. Its efficacy is such that it can be used to commence a footrot eradication program during the spread period, as demonstrated in this series of trials. Other experiences with the product (ML Colburt personal communication) suggest that an alternative approach to the use of the product during the spread period is to delay paring until prior to the third treatment. The previous two treatments are able to reduce the level of infection and thus the economic loss and the degree of paring which needs to be done. This approach needs to be tested in controlled trials; the prevailing drought conditions prevented this trial from being undertaken in the spring of 1994.

Acknowledgments

We wish to thank the principals of Colburt Holdings who funded these trials and granted permission to publish these results. Our thanks also to the farmers who made their properties and sheep available for the trials and to the District Veterinarians and Footrot Advisory officers from the relevant Rural Lands Protection Boards who assisted with the trials. Statistical analysis was provided by Les Balaam, ‘Biostat’, Bundanoon, NSW.

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(Accepted for publication 16May 1996)