8.1 In this chapter the Committee considers techniques that have been developed to undertake various aspects of OJD control. The availability of such techniques is a key factor determining the scientific feasibility of various approaches to OJD control. Where the information is available, the Committee will note the costs of particular techniques, but not their broader economic implications. These, and social implications, are considered in later chapters.
8.2 The physical nature of the disease, as discussed in the Chapter 7, influences the techniques that can be developed.1 Current research and developments, also outlined in that chapter, are likely to influence what new technical options might be available in the near future.
8.3 Generally, for each potential approach, there will be a number of actions required. For example, where containment of the disease is the objective, and quarantine is the approach, there will be a need for actions aimed at identifying contaminated properties and ensuring that the disease does not spread from these to other properties. Techniques will include testing to identify infected flocks and methods to contain infection within the contaminated property. Where eradication is the objective, the approach could be destocking and decontamination of the property. In that case the specific actions could relate to methods of decontamination, duration of destocking and testing of animals for restocking.
8.4 In this chapter the Committee will first consider some general technical aspects of managing sheep disease, then consider evidence it received in relation to specific control actions for OJD. In the next chapter it will relate these to a range of potential approaches to OJD control.
8.5 Disease organisms are favoured by particular climatic circumstances, and the risk of infection is often enhanced by increased animal density on a grazed area.2 Often disease becomes a problem when nutritional stress is placed on sheep. Poor condition can predispose sheep to infection and can also be a result of an increase in an existing low-level infection.
8.6 Wool and sheep-meat producers are alert to recurrent seasonal and regional risks of nutritionally induced disease but unusual seasons and changes in pasture composition can result in abnormal levels in some seasons.3 Major changes can occur in a matter of days and can be made worse by extreme weather events. Deficiency of nutrients, including both minerals and organic components of diet, such as amino acids, can cause ill health. So too can excess of some minerals.4 These matters are considered in more detail below.
8.7 Deaths in a sheep flock occur for a whole range of reasons, though sheep are not usually left to die of old age. They are culled from the flock at a range of ages depending on the strategies of managers.5 Apart from culling, mortality rates in reasonably well-run sheep flocks in Victoria are typically around 2 per cent per annum.
8.8 A cycle of poor animal health can increase mortality rates markedly in mature sheep, for instance, to over 5 per cent per year.6 Likewise deaths of young animals shortly after birth can be very high, particularly where the mothers are underfed and in cold wet windy weather. With good nutritional management and shelter, such losses can be reduced to 1-2 per cent.
8.9 Adequate nutrition is an essential part of ensuring good health of livestock.7 This requirement is considerably greater for pregnant and lactating ewes than for other sheep, although the demands placed on sheep that produce heavy cuts of wool are not insignificant.
8.10 Any disease that leads to inefficient absorption of nutrients (as is the case with OJD) or excessive demands on those nutrients ingested by the animal (as with intestinal parasites) will increase the need of the animal for nutrients to stay healthy.8The primary requirements are for adequate energy and protein in the fodder.9 At certain times of the year in all parts of Victoria it is common for stock to experience shortages of protein (as pasture matures and dries off in summer) and total energy, when pasture growth is restricted by shortage of water or cold weather. The results can be wasted animals and, in the extreme, death. Poor nutrition can render animals more prone to infection, parasitism or the symptoms of disease.10Deficiencies in the minerals supplied by pasture may also lead to poor health. Livestock require a number of minerals in forms that they can absorb. Required minerals can be divided into:
a) macronutrients - such as calcium, phosphorous, sodium, chlorine, potassium, sulphur and magnesium; and
b) micronutrients - such as iron, zinc, magnesium, copper, cobalt, iron, molybdenum and selenium.
8.11 Soil tests are of some use in predicting the adequacy of macronutrients for plants and animals. However, they do not indicate the availability of trace elements (micronutrients) to plants or animals - direct measurements on the plant or animal tissue are required.11In Victoria, the pasture species used are usually more sensitive to mineral deficiencies than the stock grazing on them. As a result, top dressing with micronutrients to encourage pasture growth has reduced the incidence of micronutrient deficiencies in livestock.12 An important exception is cobalt, which is required by ruminants to synthesise vitamin B12.13 Deficiencies have been identified in livestock grazed on alkaline coastal sands. Symptoms are wasting and eventual death with severe deficiency. These are not unlike the symptoms of OJD, but reversible with treatment. Copper requirements are strongly affected by the concentrations of molybdenum (which is often added to pastures as a trace element needed by plants, but not animals), sulphur and iron.
8.12 Toxicity from excess of certain minerals can also be a health problem with stock. Liver damage can result from excessive intake of copper when certain plants are consumed in large quantities, there is very low availability of molybdenum or animals are dosed with copper. Excessive application of molybdenum can precipitate copper deficiency through an interaction in the rumen that leads to a copper-molybdenum-sulphur complex.14
8.13 A range of tests to detect whether an animal is infected with OJD has been described to the Committee. These tests depend on some response in the animal to infection. Responses can be multiplication of the bacteria in the infected tissue, shedding of the bacteria, development of immune reactions - cell-mediated or serological (`blood') responses or disease symptoms, particularly changes to the gut tissue.
8.14 Surveillance depends on marrying effective testing to a system for relating results to the distribution and prevalence of the disease.
8.15 Many of those who spoke to the Committee or made written submissions referred to the inaccuracy of tests for OJD, particularly mentioning the 30 per cent sensitivity of blood tests.15 Several witnesses expressed the view that control of OJD requires a cheap and accurate test.16 Unfortunately the evidence provided to the Committee indicated that a test that can show, with 100 per cent accuracy, that animals are free of OJD is most unlikely in the foreseeable future, though improvements to tests are being made.17Prowse, in his Scientific Review, explained that the reliability of a test relates to both its `sensitivity' and `specificity'.18 The sensitivity of a test is its ability to diagnose an infected animal correctly. A test that is very sensitive will seldom incorrectly diagnose an infected animal as uninfected - that is, rarely return a false-negative result. The specificity of a test is its ability to diagnose an uninfected animal correctly. A test that is highly specific will seldom incorrectly diagnose an uninfected animal as infected - that is, rarely return a `false-positive'.
8.16 Any given test can have quite different levels of specificity and sensitivity - that is, a test which is highly specific can have low sensitivity and vice versa. This is the case with OJD. Most tests for OJD have high specificity but much lower sensitivity.19 An ideal test would have both high sensitivity and specificity, but this can be difficult to achieve.
8.17 Similarity between M. paratuberculosis and many other benign mycobacterium bacteria that occur naturally in the environment create major problems for the diagnosis of M. paratuberculosis infection.20 Identification between the ovine and bovine strain is also difficult,21as is the slow response of animals to infection.22 In spite of this there is currently an array of tests available for diagnosis of OJD infection. These use detection of the bacterium in tissue or disease symptoms, blood response or a cell-mediated immune response.23 The last method is still in the experimental stage.
8.18 The different tests are summarised in Table 8.1. Except in the case of the pooled faecal culture, where it is a group of (50) sheep that is being tested, sensitivity and specificity figures in this table refer to the reliability of the test in diagnosing the status of an individual animal.
8.19 In the early stages of infection, before animals start to shed bacteria or develop an immune response, all currently available tests will be negative. As the infection progresses different types of tests become positive - that is, are able to pick up the presence of infection. Tests have maximum sensitivity (are least likely to return a false negative) when used on animals with clinical signs of disease.24Because OJD infection is difficult to diagnose reliably in individual animals, particularly before they are showing clinical symptoms of disease, testing strategies have focused on flocks and have been based on a risk-management approach.25 It was evident to the Committee that the calculations used in the assessment of risk were not well understood by many of those
|
Test |
Biological basis |
When it is effective |
Sensitivity |
Specificity |
Comment |
|
Blood test ELISA and AGID/AGIT |
Immune response involving antibodies to M. paratuberculosis |
Generally after shedding has started but can be effective before disease symptoms appear |
20-30% with potential for improvement |
99% + |
Not suitable for individual animals, as a substantial sample from a flock is needed to provide an adequate level of reliability; needs to be repeated to show freedom from OJD; test results within days; $4-8 per animal |
|
Bacterial culture |
Isolation and culture of M. paratuberculosis from tissue |
Clinically infected animals - usually 1+ years after infection |
40-70% |
Approx. 100% |
Culture requires 7-16 weeks; $25 per test; requires experienced technologists |
|
Culture of M. paratuberculosis from faeces · BACTEC · Pooled faecal |
After shedding has started, commonly 1-2 years after infection |
50% 30-50% |
Approx. 100% 100% if no contaminat'n |
Appears to detect infection earlier than other available methods; requires experienced technologists. · 7 weeks culture; $25 per animal · 12-14 weeks culture; relatively cheap; flock test only; allows identification of freedom from disease; $1, 000 per flock |
|
|
Identification of bacteria in tissue sample |
Presence of M. paratuberculosis in tissue. |
After autopsy, when sufficient bacteria are present in tissue to be observed |
Not evaluated. |
Up to 100% |
A test to confirm infection after other tests; risk of false negative high; $60 per test; requires skilled technicians and disputed results have been reported26Gamma interferon response |
|
Gross signs + microscopic examination of tissues - autopsy of suspect sheep - abattoir surveillance |
Development of disease in intestinal tissues and related lymphatic system |
After signs of disease are visible, but before severe symptoms develop |
Not yet determined but apparently high |
Approx. 100% with microscopic examination |
Applicable to widespread monitoring and, potentially, identification of infected and `clean' flocks; relatively cheap - < 70 cents per animal inspected; requires trained technicians; an apparently positive result is conformed by microscopic examination. |
Sources: Johne's Information Centre (1999), Allworth, B. (2000), National OJD Operations Co-ordinator, personal communication, 7 June 2000 and Prowse (2000).
making submissions to the Inquiry and possibly not by some field staff who had to undertake the testing.
8.20 From material provided in the Prowse Report, it is the Committee's understanding that none of the available tests can measure with absolute certainty whether an individual sheep or flock is OJD free. A realistic goal of flock testing that has been generally adopted is to provide a 95 per cent probability of detecting the disease where present in at least 2 per cent of the animals tested. The number of samples required to obtain a confidence level of 95 per cent will vary according to the size of the flock. The larger the flock, the more samples will be required to achieve the 95 per cent confidence level.
8.21 A test technique of say 50 per cent sensitivity will detect half of the infected animals in the flock sample. That means that if there are say six infected sheep in the sample, three will return a positive test result (although there is always a chance that the sample taken will not produce an `average' result). It is possible, however, that not even one infected sheep will be detected even though the flock is actually infected - but this probability is less than 5 per cent - in other words there is a 95 per cent probability that the infection in the flock will be detected if 300 sheep are sampled.
8.22 The Committee identified a number of issues arising out of the assumptions made in these calculations. The first is that they assume that 2 per cent of the flock is not only infected, but that infection has progressed to a stage where the test will detect it. As the Committee discussed in Chapter 7, the initial spread of OJD through a flock can be slow. How long it will take after an infected animal is introduced into a flock for prevalence of infection to build up to 2 per cent is not clear, but the available evidence suggests that it could be a year or more. After that the disease must develop to a stage where the available tests can detect it. This may involve another one to two years. Though several witnesses have described available tests, particularly the blood tests, as accurate on a flock basis, it appears that they may not be accurate for as much as two to three years after a flock becomes infected.27 A negative test result thus may indicate that prevalence of infection is low or recent rather than that it is absent.
8.23 Though no current test can detect early infection in a flock, incorporating the poorest sheep into the sample that is tested should increase the sensitivity of the test.28 This is because the prevalence of infection, if it is present, should be highest in these sheep. According to Dr Prowse:
Tests have maximum sensitivity when used on animals with clinical signs of the infection, diarrhoea and/or weight loss. Unfortunately, exceptions to these generalisations are common. For this reason, when confidence in the absence of M. paratuberculosis infection is desired, the use of two or more different types of tests at the same time is recommended.29Considering the implications of a positive test, scientists have suggested that the same caution should be applied there too - that is, any positive test should be confirmed by a second test.30National testing standards, as prescribed in the National Standard Definitions and Rules, take these factors into consideration, but accept some level of risk.31 In particular, repeated testing every two years is required to maintain the status of a flock as free of infection, and confirmation of infected status by a follow-up test is now normal practice.32The particular difficulties identified by the Committee in relation to all tests, but particularly the blood tests, include:
a) excessive cost to undertake flock testing ($1,800 per flock using blood test);33low sensitivity at the individual animal level and smaller, but significant risk of error at the flock level;
b) inability to detect M. paratuberculosis before shedding has started;34their low capacity to identify flocks and properties that are free of OJD; and
c) the length of time to obtain results of tests, particularly those involving culture of the bacterium.
8.24 The last difficulty, as Associate Professor Vizard pointed out, is particularly important for, in any control and eradication program, "the greater job is not to identify diseased properties but to clearly show those properties that do not have disease".35Blood Tests
8.25 The blood tests measure antibodies to M. paratuberculosis in the infected animal's blood. The tests are quick and can be used appropriately on animals two years and older.36Dr Prowse indicated that the way in which the blood tests are applied should be related to the outcome that is required. In other words:
If a blood test is done and positives are found in a number of animals in a flock, there is the likelihood that that flock is infected. That needs to be followed up and coupled with another confirmatory test, possibly in conjunction with a post-mortem examination and perhaps some examination of tissues by a pathologist to confirm that the disease exists in a flock.
However, it is a different issue if we look at using a blood test to demonstrate freedom from the disease because you need to test a certain number of animals to get a particular level of confidence that the flock is free from disease ... there is always the possibility that at a later date the same flock may test positive. If it tests negative at one stage you have a possibility that the flock is free from disease, but if you test it later it could conceivably test positive either because of the failure of the first test to expose it early in the development of the disease and a new response had not developed or that the test was not sensitive enough to pick up the infection in the first place. It requires repeat testing to get confidence that a flock is free from infection.37Pooled Faecal Culture
8.26 The pooled faecal culture test was developed by NSW Agriculture. Development of tests dependent on culturing the ovine strain of M. paratuberculosis was hampered until 1998 because it was only then that successful culture techniques for the strain were developed.38
8.27 According to Prowse, the pooled faecal culture test adapts standard culture techniques to identify M. paratuberculosis bacteria in a pooled sample of faecal pellets from a `pool' of up to fifty sheep.39 Smaller pools of sheep, or even individuals, could be tested if the animals were of particularly high value.40 At this stage it appears that this method may be more sensitive than the blood tests and is effective at an earlier stage in infection. Unlike blood or gamma interferon tests, it is also not affected by vaccination using a killed vaccine (see below).
8.28 Drawbacks of the test are the fairly long time that is required for culture (12-14 weeks), inability to detect which animal in the pool is infected when a positive result is returned and risk of contamination that can produce false positives.
8.29 NSW Agriculture evaluated the procedure as part of the National OJD Program.41 In May 2000 it was approved as a nationally accepted diagnostic test.42 Staff of two Victorian veterinary laboratories have recently completed the required training in the technique and the Department of Natural Resources and Environment hopes to have other laboratories approved to conduct the required diagnostic procedures in the near future.
8.30 Abattoir surveillance has only recently become available, as the routine procedure is still undergoing some further development and evaluation. The method was pioneered and developed in Victoria but is being refined in NSW, where the large number of infected flocks made its further development and assessment more effective.43 As noted in Chapter 5, abattoir surveillance has been done on a limited scale in Victoria and plans are in place to expand the use of this form of testing.
8.31 The method involves the inspection of the intestines of sheep at the time of slaughter. Quite early in the infection process there are often changes in the wall of the intestines and associated lymph glands. These can be identified by a trained person.44The Committee observed this procedure in practice during its field inspections in NSW. A `line' of sheep is inspected as a unit. This commonly, though not always, represents a flock from a known source.45 A large sample of sheep from the line are inspected. Tissue samples from sheep that appear to have symptoms of OJD are sent for histopathological (microscopic) examination.
8.32 Advantages of the method that have been highlighted to the Committee are:46its potential to screen virtually all lines of sheep that are sent to slaughter and produce an accurate picture of the distribution and prevalence of OJD;
a) its capacity to detect infection before it has reached high prevalence in a flock;
b) its potential to maintain surveillance at relatively low cost;
c) the fact that it is not affected by vaccination against OJD (discussed below); and
d) its potential to avoid the perceived unfairness associated with testing only those flocks identified through trace forward or trace back from known infected flocks.
8.33 Costs to detect infected flocks are lower with abattoir surveillance than with blood testing. When testing and surveillance are being undertaken to detect infected flocks, a large number of uninfected flocks will be tested to find a few infected ones. This increases the cost of finding the infected flocks. Consequently the cost of finding infected flocks will increase as the proportion of such flocks falls, although focusing testing on those flocks most at risk (for example, by selecting flocks of older sheep, identified by trace forward or in localities with known high incidence of infected flocks) will reduce the average cost of finding infected flocks.
8.34 According to Dr B. Allworth, National OJD Co-ordinator, the cost of detecting an infected flock by tracing and blood test costs approximately $40,000 compared with $1, 000 by abattoir surveillance.47 These estimates allow for the higher incidence of infected flocks in NSW than in Victoria. In Victoria, where more of the flocks tested will be uninfected, the average cost to find an infected flock can be expected to be higher than the figures given by Dr Allworth, but the relative cost using abattoir surveillance would still be lower than with blood testing.
8.35 Several disadvantages of the method have been identified by the Committee. Specifically:
a) it does not identify recent infections in flocks (only advanced infection is picked up);48where only aged stock is sold for slaughter (as with studs and flocks run for wool) the infection could be present on a property for years before it is identified;
b) there is a need for adequate histopathological backup on a reasonably large scale (depending on the prevalence of infection);
c) clear identification of the source of carcasses is needed if the method is to be used to identify infected flocks or individual animals; and
d) there is a small risk of cross-contamination or confusion of the identity of a carcass on the abattoir line, so that a positive identification must be confirmed by further testing.49The Gamma Interferon Test
8.36 The Committee, during its inspection of the CSIRO's Australian Animal Health Laboratories, saw work in progress on the development of the `gamma interferon' test. As explained in the Chapter 5, this test depends on chemicals released during the early immune response of animals to M. paratuberculosis, when there is a build-up of white blood cells that are adapted to destroying this particular bacterium.
8.37 A test based on this response played an important part in detection and eradication of bovine tuberculosis. Development of a similar test for M. paratuberculosis has proved difficult, but recent work being done by CSIRO is making good progress.50 The test has been described as having great potential for early diagnosis of infection at a stage when existing blood and faecal culture are ineffective. The need now is to improve the test, which is currently in the experimental stage.51The most likely disadvantage of the test, at least initially, will be its cost. This is likely to limit its use to high-value animals such as rams.52Finding 8.1
All available tests have disadvantages, but if these are recognised, together the tests provide a useful array of techniques that cover most requirements for testing. The development of a cheap test that has high sensitivity and specificity on individual animals remains elusive and should be a priority of research. The gamma interferon test being developed by the CSIRO offers potential to meet these requirements.
8.38 The reliability of tests depends not only on the physical limitations of the tests, but also on how well they are carried out. The Committee was made aware of concerns about procedures at several levels. Evidence presented suggests that there is cause for concern with respect to quality control at the laboratory level, in the selection of animals to be tested and in the integrity of identification of animals tested from the paddock to the final reporting of results. These were discussed more fully in Chapter 6, where aspects of program delivery were considered, while the quality-control procedures in place are outlined below.
8.39 The Committee was told that quality control is provided for laboratories through a voluntary accreditation procedure under the Australian National Quality Assurance Program. The Program facilitates quality assurance in twenty-two government and private laboratories in Australia and New Zealand. The method of evaluation involves different laboratories undertaking the same procedure on test samples and comparisons being made of results. Accreditation is a requirement for registration of a laboratory in Victoria. The process assesses the capacity of laboratories to perform procedures accurately rather than how they actually perform on a day-to-day basis.
8.40 The National Serum Panel in Australia provides quality control for blood tests. Quality control for faecal culture was described as "disappointing" by the Panel, although it did not expand on why it considered this to be the case. 53The Department of Natural Resources and Environment told the Committee that there is also a national standard relating to laboratory testing for OJD endorsed by the Standing Committee on Agriculture and Resource Management.54 The National Standard includes:
a) accredited laboratory operating procedures;
b) standard techniques published in the Australian and New Zealand Standard Protocols;
c) proficiency testing of laboratories through the Australian National Quality Assurance Program; and
d) a Quality Plan for Johne's disease.
8.41 The Victorian Institute of Animal Science is the national reference laboratory for Johne's disease and is recognised by the World Animal Health Organisation as an international reference laboratory.55 In this capacity it monitors quality assurance for Johne's disease diagnosis by Australian and New Zealand laboratories.
8.42 Other testing for OJD in Victoria has been conducted at Victorian Pathology Services. Dr Kefford said:
Both laboratories are certified in accordance with ISO 9002 and accredited by NATA under the new ISO/IEC 17025 provisions. This certification and accreditation applies to the quality systems in place in each laboratory. The systems are subject to regular internal and external audit.56Dr Kefford further said that, under Australian National Quality Assurance Program requirements, the AGID blood test for OJD and OJD culture are subject to two rounds of proficiency testing each year.57Although a bacteriological assurance program that includes the culture and identification of M. paratuberculosis has been reported as being in place,58staff of the Australian National Quality Assurance Program told the Committee that an accreditation procedure for OJD tests is only in the development stage and not yet implemented.59Flock or Animal Identification
8.43 For sheep slaughtered for autopsy, Dr Kefford described a `chain of evidence' already used to ensure the identification of specimens from source to final diagnosis.60 It is not clear to the Committee how long the procedure has been in place or how its effectiveness is verified.
8.44 The Committee noted the value of identifying flocks or individual animals as a means of extending the usefulness of abattoir surveillance. It could be particularly useful in clearing flocks from suspicion.61 Identification of individual animals plays an important role in the control of cattle disease.62 This is not necessarily as simple with sheep. 63 However, a reliable identification procedure could provide other useful management tools for farmers, such as feedback on carcass quality. In addition, European countries are currently requiring trace of individual animals through slaughter.64 These factors might encourage participation.
8.45 Sheep identification is difficult because of the added cost involved for animals that are less valuable than cattle, the impracticability of branding and the risk of ear tags being lost. Techniques currently in use include ear tags and using a trail of records from sale to abattoir. Neither is used consistently.65 At the saleyard there is a diversity of systems for keeping records of sheep passing through the yards.66 However, the Sheepmeat Council is investigating ways to overcome this problem. Expressions of interest are being sought through Meat and Livestock Australia to investigate a sheep identification system.67Two approaches have been advocated. Some suggest that each sheep be tagged to identify its home property. Others have suggested that each sheep be tagged with an individual identifier.
8.46 Techniques increasingly used in the identification of domestic animals such as microchip implants may offer advantages over tags, such as reliability and resistance to loss or manipulation.
Identification of sheep is a little-used technique in the sheep industry, but a technique that has a number of important applications.
8.47 The Committee received evidence that vaccination can reduce the impacts of disease on a flock and may also have a place in reducing pasture contamination.
8.48 Work undertaken in Greece showed that use of a killed vaccine reduced the number of sheep shedding M. paratuberculosis from 19.6 per cent to 1.9 per cent in a flock, reduced expression of OJD by 90 per cent and mortalities from 22.7 per cent to 2 per cent. In a study of a New Zealand sheep flock, clinical reductions due to vaccination were, in clinical expression, from 242 to 233 sheep and in mortalities from 41 to 7.68 And, as was outlined Chapter 4, several decades of compulsory vaccination appear to have achieved eradication of OJD in some, but not all, regions of Iceland. In Norway the use of goat vaccination for seven years achieved eradication.69Dr H. Millar, Victoria's Chief Veterinary Officer, expressed a less-optimistic view:
It [vaccination] is not in itself an effective disease control measure because it does not stop sheep becoming infected.70
8.49 This is because current vaccines depend on stimulating an antibody response rather than preventing infection. As it does not stop infection, consequently shedding of bacteria is not prevented. It may, however, reduce the shedding of bacteria substantially.71
8.50 As a consequence, there is a possibility that it could contribute to eradication of OJD in heavily infected areas by progressively reducing prevalence of the disease. 72 The possibility of eradication of OJD from a property or region would be increased if complemented by management at the farm level using minimisation approaches (see Chapter 9) and restriction of movement between farms.73
8.51 Because the development of a new vaccine takes years, an existing killed vaccine (the Gudair vaccine) has been imported from Spain for testing in Australia as part of the National OJD Program. Dr A. Britten, Veterinary Service Manager with CSL Ltd, described the vaccine and early test results to the Committee.74 As a killed vaccine Gudair poses no risk of introducing new strains of M. paratuberculosis. Nor will it interfere with any test that depends on culturing the bacterium or recognising symptoms of the disease. It would, however, interfere with blood tests and the gamma interferon test, as it will stimulate antibody and white blood cell responses in animals.
8.52 With respect to reported damage of some vaccinations to the sheep's carcass,75Dr Britton stated that early research results suggest that such damage will be minimal.76 Only one vaccination is needed to provide the animal with protection from OJD symptoms. No subsequent vaccination is needed. She estimated that the total cost, including administration of the vaccine, is approximately $2 per vaccination.
8.53 A new vaccine (described in Chapter 7) is being developed by CSIRO. This should not only overcome the problem with currently available vaccines - in particular interfering with blood and gamma interferon testing - but is also expected to prove inexpensive and to have little impact on carcass quality.77 Development is likely to take some years, however.
8.54 In the longer term, a vaccine that can restrict or prevent infection and can be administered orally is not impossible, but such a vaccine would take many years and substantial investment to develop.78Finding 8.3
Where used, vaccination techniques appear effective in reducing the symptoms of the disease and, as they also reduce shedding, may offer a long-term method of eradicating the disease from a property without need for total destocking.
8.55 Decontamination of pastures and water supplies within paddocks requires that the concentration of M. paratuberculosis bacteria anywhere in the paddock be reduced to a level where it cannot lead to infection of an animal. The techniques are based on the knowledge that the M. paratuberculosis does not multiply in the environment and, if the climate and environmental factors remain constant, the amount of contamination follows an exponential decay curve.79 Hence the level of initial infection will determine the period before the contamination drops below the critical point for an effective dose.
8.56 Destocking is a radical but effective technique to decontaminate pastures - it involves the total removal of all animals that could be shedding the bacterium. Decontamination under the Victorian OJD Program was based on the assumption that it could be achieved by removing infected sheep for a period of at least fifteen months, including two summers.80
8.57 As noted in Chapter 7, current research indicates that this policy assumption still holds. Research in progress, at the University of Sydney, appears to indicate that the minimum period required to decontaminate pastures and localities may be able to be reduced in the future. 81
8.58 The technique relies on ensuring that there is no reinfection - see section below.
8.59 Evidence was received by the Committee that total destocking was the only way to achieve decontamination.82 An alternative to destocking the whole property at one time is to destock it in sections.
8.60 Whether the whole or only part of the property is destocked, the object is to remove the source of ongoing contamination while bacteria on the pasture are killed by exposure to environmental elements, such as ultraviolet radiation, heat and desiccation. Because bacteria would be most likely to survive longest in shaded, swampy and damp areas, it has commonly been recommended that these areas should be fenced out before stock are returned to paddocks.83
8.61 Others presented evidence that a slower, gradual reduction in contamination through other forms of management may also lead to decontamination.84 The latter approach is discussed below.
8.62 Reducing the number of M. paratuberculosis organisms ingested by susceptible animals (the challenge to the animal) reduces the likelihood that individual animals become infected. Consequently, reduced pasture contamination lowers the prevalence of the disease in a flock. For animals that do become infected, a reduced bacterial load will delay the build-up of infection in the animal, faecal shedding of the bacteria and onset of clinical symptoms.85 It is therefore possible that management that concentrates on minimising contamination can eventually reduce the infection load on pastures to the point where the infection dies out. Dr L. Denholm, research veterinarian with NSW Agriculture, estimated that, under certain conditions, decontamination could be achieved in ten years or two generations of sheep without total destocking.86Several methods have been proposed to minimise contamination of pastures with M. paratuberculosis. These include:
a) isolating and culling suspect sheep to minimise shedding of the bacteria;87
b) using a period of cropping or grazing by uninfected animals (including young uninfected sheep subsequently consigned to slaughter at less than a year old) to allow natural decontamination of a paddock;
c) running a young flock; and
d) good animal husbandry (as outlined below under techniques to reduce prevalence in the flock). 88
8.63 Culling of likely diseased animals may be facilitated by testing of all animals, or those at risk, and culling any that test positive. This `test-and-cull' method is used for control of Johne's disease of cattle and was successful for eradication of bovine brucellosis and tuberculosis.89 In Australia a number of objections have been raised to test-and-cull for eradication of OJD. These are the inability of current tests to detect infected individuals before they start shedding bacteria, the high cost of testing relative to the value of individual animals and the potential of sheep to become infected at any age so that testing must be repeated.90 Some have concluded that as a means of eradicating OJD, test-and-cull is not practical.
8.64 However, one New South Wales researcher suggested that, for more-valuable sheep, particularly stud rams, use of pooled faecal culture as the test method on small groups and individuals, repeated over a period of months, might prove a practical way to use test-and-cull to eliminate infection without total destocking.91Vaccination
8.65 As noted above, vaccination might have a role to play in reducing pasture contamination, as research indicates that it may substantially reduce the shedding of bacteria by infected sheep.
Destocking, combined with spelling of paddocks for two summers, is currently the most effective method of eradicating a disease from a property.
8.66 Containment of OJD involves preventing the spread of the disease to new properties or locations. It is one of the main objectives of the National OJD Program. 92
8.67 As the Committee explained in Chapter 7, the main way that OJD is spread is through the movement of infected animals that are shedding the bacterium. By far the greatest risk comes from infected sheep or domestic goats, traded or straying from their property of origin. However, the Committee has been presented with evidence suggesting that feral animals could present some lesser risk. There is also a potential for spread of infection as a result of overland flow of water carrying infected faeces from property to property or poor hygiene during transport, sale or disposal of sheep and their waste.
8.68 Good boundary fences, including double fences, and regular checking of the flock, fences and gates are recommended by NSW Agriculture and the Department of Natural Resources and Environment to avoid escape of OJD via stray sheep or feral animals.93 Though the risk of introducing the disease through run-off is thought to be small, use of double fencing with a well-vegetated space between the fences to trap faecal material, and drains to prevent water from running off the contaminated property to neighbouring land, are also recommended. Dense groundcover between the fences will make the barrier more effective.
8.69 The Committee, during its field inspections, noted that the character of the land might influence the difficulty of providing a barrier to contamination at the property boundary.94 Steep hills, deep drainage lines and flash flooding can make it difficult to maintain a barrier to movement of faeces in water. Double fencing and fences that are proof against feral goats are expensive and may not prevent movement of faeces by flood-waters in localities, such as parts of south Gippsland, where large areas can be covered by floods.95 Sheep droppings can float and, as one farmer described at the Yarram hearing:
Our property has more than 300 hectares under water during a flood event, and most properties experience widespread water movement after heavy rainfall events.96It was explained to the Committee that containment needs be tailored to the circumstances of a particular property.97 The containment plan for one central Victorian farmer's property takes account of the location of sheep campsites, water flow patterns and proximity of neighbouring stock.
8.70 The Committee was also told of the difficulty posed by the rare, careless farmer who makes little effort to prevent straying of infected stock, and well-meaning passers-by who sometimes chase stock from roads into the nearest paddock. These are human issues that need to be addressed if containment techniques are not to be compromised.
8.71 The Committee was made aware of the risks of spreading OJD through saleyards, shows and trucking of sheep.98
8.72 The Committee sought evidence concerning the risk of transmission of OJD through saleyards. According to Mr F. White, Executive Officer, Livestock Saleyards Association of Victoria, saleyard hygiene processes and methods of waste disposal vary greatly across the State.99 Major saleyards operate under a quality-assurance system known as national saleyards quality assurance. The required control technique involves a complete cleaning of the yard after every sale. Mr. White recalled that the previous Chief Veterinary Officer in Victoria, Dr Andrew Turner, considered the washing of concrete or asphalted yards to provide satisfactory cleaning.
8.73 As noted in Chapter 5, the disposal of infected abattoir waste can potentially spread infection. Current disposal techniques are not designed to contain OJD and they appear to be ineffective - improved control techniques are required.
8.74 NSW Agriculture pointed out the need to ensure that OJD is not spread through contaminated trucks. It recommends thorough wash-down of trucks used to transport sheep.100 Disposal of the waste waters used in the wash-down of trucks or saleyards then becomes an issue.
8.75 The risk of cross-contamination at livestock shows is largely addressed by restrictions on the showing of infected sheep. Some show organisers now require sheep to be tested under the Market Assurance Program before they will be accepted at shows.101Finding 8.5
Without the use of containment techniques, the disease will spread. In many applications, hygiene and waste disposal techniques are ill defined.
8.76 As the Committee explains in Chapter 9, reducing contamination of pastures, even if not successful in totally eliminating contamination, will reduce the risk of both infection and expression of the disease. Consequently, reducing pasture contamination, as described above, is the primary method of reducing prevalence of OJD within a flock. Other factors have to do with minimising exposure of the most susceptible animals and maximising the resistance of the stock to infection and expression of the diseases.
8.77 The most susceptible animals are lambs. Management systems that ensure lambs, particularly weaners, are run on minimally contaminated pastures have been recommended by leading researchers.102 They also recommended that replacement stock should be introduced onto low-risk (low-contamination) pastures. During its field inspections the Committee was able to see such a practice being successfully used to maintain low infection rates.103
8.78 Sheep yards and holding paddocks are likely to be particularly heavily contaminated. NSW Agriculture recommends that, where possible, the use of holding paddocks should be avoided when young sheep are being handled. 104Reducing Expression of Disease
8.79 Evidence was presented to the Committee that stress from any cause, whether inadequate nutrition, parasites or extremes of temperature, particularly after shearing, appears capable of bringing on clinical disease or making it worse. Good husbandry to avoid such stresses is widely recommended as a way to reduce the prevalence and impact of OJD.105
8.80 Dr Prowse, in his evidence to the Committee, had some reservations about this approach.106 He considers that properly controlled experiments are needed to establish what can be achieved by minimising stress. Evidence provided to the Committee on the benefits of reducing stress was anecdotal. It is not clear that reducing stress alone can keep prevalence of OJD to a low level indefinitely, or which forms of stress might be most relevant. Indeed the Committee was provided with evidence, during its inspection tour of NSW, that very high standards of management have not always succeeded in preventing escalating impacts of the disease in the long term.107 Experience of OJD under Victorian conditions is too short for the Committee to draw firm conclusions about the efficacy of management to control OJD in this State. Nor would it seem possible to shield sheep from all stresses all the time, even on the best-managed properties.
8.81 Assertions have been made to the Committee that manipulation of soils, particularly soil pH and copper levels, can cure or minimise OJD.108 The Committee has found no evidence that this is the case. Although, as discussed in Chapter 7, there has sometimes been found to be a connection between OJD incidence and acid soils, no experiments to treat OJD by manipulating soil pH have been identified. Nor has any evidence been found to suggest that treating sheep with copper will either prevent or cure OJD. In fact, according to Dr W. Sykes, veterinary researcher and consultant, the suggestion that copper could be used to cure OJD is potentially dangerous, because copper can be toxic when used in animals that already have sufficient levels.109
8.82 At the same time, attention to any actual nutrient deficiencies, including trace element deficiencies, would be part of minimising dietary stress.
8.83 There is evidence that some breeds of sheep are more resistant to OJD than others.110 In fact the breed in which OJD was introduced to Iceland, though carrying the infection, never exhibited symptoms.111 As indicated in Chapter 7, British breeds appear to be less susceptible to the disease than are merinos. Evidence for resistance is tenuous at the moment, however, and the Committee sees little immediate scope for selecting for disease resistance with such a slow-developing and insidious disease.
8.84 As noted above, current vaccinations will not prevent infection, but research indicates that they may reduce symptoms and mortality rates in infected sheep.
8.85 M. paratuberculosis is resistant to most antibiotics.112 There are a few drugs that produce some temporary reduction in symptoms but do not cure the disease.113 Treatment is seldom attempted, as the cost of drugs and the length of time for which they must be used make them prohibitively expensive for livestock. Results are generally poor and, as they at best only suppress the infection for a period, there is little to be gained from their use.
8.86 M. paratuberculosis is also resistant to common disinfectants. Phenolic and cresylis disinfectants are effective, but their toxicity means that they are inappropriate for broad scale application. They could be used where there are small quantities of concentrated contamination, such as in a laboratory situation.
An array of `on-farm minimisation' techniques may have application in reducing the prevalence of OJD, but they appear less suited, at least in the short term, to achieving eradication.
8.87 The risk of reinfection of flocks after OJD has been eliminated from a property appears to be causing considerable concern to farmers. Mr G. Simpson, District Veterinarian with the NSW Central Tablelands Rural Lands Protection Board, reported to the Committee that reinfection after destocking has occurred in NSW.114 There have also been unconfirmed reports of properties being reinfected in Victoria after a period of decontamination.115 The Committee identified several potential sources of reinfection. These are:
a) areas that have not been fully decontaminated;
b) alternative stock or hay that may carry the infection;
c) replacement sheep for restocking;
d) stray or feral animals; and
e) faeces washed from neighbouring properties.
8.88 Factors that might delay the process of pasture decontamination are described in Chapter 7. These are particularly to be found in cool, moist areas. Because of this, fencing out such areas has sometimes been required before restocking is permitted to minimise the risk of reinfection.116Alternative Stock
8.89 Many farmers who had destocked their properties of sheep told the Committee that they have run cattle during the destocking period. Some are concerned that cattle could become infected with OJD and shed the bacterium onto pastures, in this way perpetuating contamination. The Committee noted in Chapter 7 that infection of cattle by the sheep strain of M. paratuberculosis is uncommon and that cattle are resistant to infection with any strain except as calves.
8.90 According to one expert, even if transmission of infection between sheep and cattle is uncommon, it might be sufficient to cause breakdown in a few destocked properties - resulting in failure of the current method of eradication.117 Prowse recommends that, in order to avoid the risk of recontaminating pastures with OJD during destocking, only adult cattle should be grazed.118
8.91 Grazing of clean lambs for less than twelve months has also been suggested as an alternative enterprise.119 The lambs would be consigned to slaughter at the end of this period. This approach is based on research that indicates that sheep will generally not start to shed until twelve months after they become infected.120Risk from Hay
8.92 Cutting of hay was suggested to one producer as an alternative enterprise during a decontamination period, and has been used in this way in NSW.121 According to the Manual of Procedures for Animal Health and Welfare Programs, Victoria, there is no restriction on the sale of hay from infected farms. However:
It cannot be guaranteed that hay made on these farms is not contaminated [from] faecel material containing the bacteria that cause ovine Johne's disease. For this reason, while hay from these farms is suitable for feeding cattle and horses, it is recommended that it should not be fed to susceptible species (i.e. sheep, goats, deer and camelids).122The Manual further adds:
This recommendation is made in the interest of the owners [of the contaminated property] given that the Trade Practices legislation requires that goods sold need to be fit for the purpose intended, and it is unlikely that they can guarantee that hay from this farm is free from contamination with ovine Johne's disease organisms.123It appears to the Committee that the risk of contamination of hay by OJD would considerably restrict the opportunity to use hay as an alternative enterprise during the period of destocking.
8.93 Destocking can only be an effective means of eradicating OJD from a property where sheep are to be run again if a source of uninfected sheep is available for restocking.124Many witnesses to the Inquiry raised their concerns over finding a guaranteed source of uninfected sheep of suitable style.125 One approach that is recommended and has been practised by several of the farmers who spoke with the Committee, is to obtain replacement stock from districts in which no OJD has been identified.126In addition, the purchaser can request vendors to test their sheep for OJD, buy sheep that have been tested under the Sheep Market Assurance Program or, at least, require a written vendor declaration of freedom from OJD.127 The Market Assurance Program, described in Chapter 4, sets out specific testing and property-management requirements for flock to enter the program and retain their `assessed' status. But such certified sheep may be difficult to procure.
8.94 The same steps that the Committee identified under `Containment' to prevent stock from straying from a property can be used to exclude stray animals - that is, good fences and regular inspection of the flock, gates and fences.
8.95 The risk from feral animals, particularly from goats, deer, rabbits and wildlife, has been mentioned in many submissions to the Inquiry.128 The Committee found that some research is being done to quantify this risk (see Chapter 7). Early results suggest that wildlife, deer and rabbits are most unlikely to provide a source of infection.129 Dr D. Pemberten, former pathologist and research veterinarian with the Department and Natural Resources and Environment, warned the Committee that feral goats pose a significant threat to OJD control and eradication. 130 Exclusion of goats seems to be most desirable, but the Committee has been told that this can be difficult in the more mountainous parts of the State.131Wash of Faeces
8.96 Dr B Allworth, Co-ordinator of the National OJD Program, told the Committee that wash of infected faeces from one property to another could present a serious risk of reinfection in some situations.132 Again, the techniques identified under `Containment' to prevent wash of faeces from a property would be appropriate to exclude infected faeces - that is, providing barriers to water movement in the forms of drains and vegetation filters on the property boundary.
Control techniques for avoiding reinfection are many, but none totally risk proof.
8.97 Loss of the `blood line', the genetic resource acquired through generations of breeding, was one of the biggest issues identified by many sheep farmers in relation to destocking as a means of eradicating OJD. Where the flock concerned is a leading stud, the loss could affect the whole industry, not simply the individual producer.133
8.98 A protocol for genetic preservation is being prepared by Animal Health Australia but is not yet available.134 The Committee identified three approaches to retaining the genetic resource in a flock. These are:
a) embryo transplant;
b) artificial insemination; and
c) identification and retention of uninfected animals from the flock.
8.99 Research is currently being done to determine the risk of infection through artificial breeding (see Chapter 7). This appears to be very low. 135
8.100 Embryo transplant and artificial insemination are methods by which valuable genetic material can be transferred to uninfected sheep. For normal commercial flocks these methods are excessively expensive because they are labour intensive. However, they have been recommended as ways to retain the genetics of infected stud flocks or to introduce new genetic material without the risks associated with buying new rams.136
8.101 Technically it would be possible to isolate very valuable animals and test them several times over a long enough period to provide a high level of confidence that they are uninfected. Infected animals would be culled. Dr L. Denholm suggested this approach for the most valuable stud rams.137 His proposal was to use a faecal culture test, either on small groups of rams or on individuals. After a period of one to two years the rams could be used on uncontaminated pastures. In the interval they could provide semen.
Control techniques for preserving genetic resources are limited and expensive, but may be attractive for certain applications, such as in maintaining the genetic resources of high-value stud.
1 Kefford, B. (2000), Executive Director Agriculture, Department of Natural Resources and Environment, Minutes of Evidence, 7 August 2000.
2 Egan and Malcolm (2000).
3 Egan and Malcolm (2000).
4 Hoskins, Caple, Halpin, Brown, Paynter, Conley and North-Coombes (1986).
5 Egan and Malcolm (2000).
6 Egan and Malcolm (2000).
7 Egan and Malcolm (2000).
8 Egan and Malcolm (2000).
9 Reid (1981), p. 428.
10 Reid (1981), p. 489.
11 Hoskins, Caple, Halpin, Brown, Paynter, Conley and North-Coombes (1986).
12 Hoskins, Caple, Halpin, Brown, Paynter, Conley and North-Coombes (1986), p. 9.
13 Hoskins, Caple, Halpin, Brown, Paynter, Conley and North-Coombes (1986), pp. 29-34.
14 Hoskins, Caple, Halpin, Brown, Paynter, Conley and North-Coombes (1986), pp. 9-10, 16.
15 For example, Blennerhassett, B. (2000), Written Submissions, OJD 001.
16 For example, Hammond, G. (2000), Written Submissions, OJD 047.
17 NSW Agriculture (1999d).
18 Prowse (2000), pp. 18-19.
19 Prowse (2000), p. 20.
20 Prowse (2000), p. 7.
21 The Committee understands that DNA testing may be required for positive identification of these two strains of the disease.
22 Kefford, B. (2000), Executive Director Agriculture, Department of Natural Resources and Environment, Minutes of Evidence, 7 August 2000.
23 Johne's Information Centre (1999).
24 Johne's Information Centre (1999).
25 Kefford, B. (2000), Executive Director, Agriculture, Department of Natural Resources and Environment, Minutes of Evidence, 7 August 2000.
26 For example, Clark, A. and I. (2000), Written Submissions, OJD 040. Copies of the reports were submitted to the Melbourne Hearing of the Senate Rural and Regional Affairs and Transport Joint Investigatory Committee on 21 July 2000.
27 Millar, H. W. (2000), Acting Chief Veterinary Officer, Department of Natural Resources and Environment; and also Prowse, S. (2000), Program Manager, Infectious Diseases and Food Safety, Animal Health Laboratories, CSIRO, personal communication, 24 July 2000.
28 Prowse (2000), p. 19.
29 Prowse (2000), p. 19.
30 Prowse, S. (2000), Program Manager, Infectious Diseases and Food Safety, Australian Animal Health Laboratories, CSIRO, Geelong, personal communication, 17 March and 12 April 2000.
31 Kefford, B. (2000), Executive Director Agriculture, Department of Natural Resources and Environment, Minutes of Evidence, 7 August 2000.
32 Veterinary Committee (1998); and also Prowse (2000), p. 35.
33 Prowse (2000), p. 35.
34 Whittington (1999).
35 Visard, A. (2000), Mackinnon Project, University of Melbourne, Minutes of Evidence, 24 July 2000.
36 Prowse (2000), p. 23.
37 Prowse, S. (2000), Program Manager Infectious Diseases and Food Safety, Animal Health Laboratories, CSIRO, Minutes of Evidence, 24 July 2000.
38 Allworth, B. (2000), National OJD Operations Co-ordinator, personal communication, 7 June 2000.
39 Prowse (2000), p. 21.
40 Denholm, L. (2000), NSW Agriculture, personal communication, 8 June 2000.
41 Whittington, R. (2000), NSW Agriculture, personal communication, 8 June 2000.
42 Galvin, J. (2000), Manager, Animal Health Operations, Department of Natural Resources and Environment, personal communication, 20 September 2000.
43 Prowse (2000), pp. 24-6.
44 Prowse (2000), p. 25.
45 Denholm, L. (2000), NSW Agriculture, personal communication, 8 June 2000.
46 Prowse (2000), p. 25; and also Denholm, L. (2000), NSW Agriculture, personal communication, 8 June 2000 and Pemberton, D. (2000), veterinarian, Minutes of Evidence, 24 July 2000.
47 Figures quoted in Prowse (2000), p. 25.
48 Visard, A. (2000), Mackinnon Project, University of Melbourne, Minutes of Evidence, 24 July 2000.
49 Roth, I. (2000), Program Manager Wool and Sheep Meat Services, NSW Agriculture, personal communication, 3 July 2000.
50 Whittington (1999).
51 Meat and Livestock Australia (1999), p. 57.
52 Prowse (2000), p. 24.
53 Meat and Livestock Australia (1999), p. 10.
54 Kefford, B. (2000), Executive Director, Agriculture, Department of Natural Resources and Environment, correspondence, VT/001/0001, received 22 September 2000.
55 Kefford, B. (2000), Executive Director, Agriculture, Department of Natural Resources and Environment, correspondence, VT/001/0001, received 22 September 2000.
56 Kefford, B. (2000), Executive Director, Agriculture, Department of Natural Resources and Environment, correspondence, VT/001/0001, dated 22 September 2000.
57 Kefford, B. (2000), Executive Director, Agriculture, Department of Natural Resources and Environment, correspondence, VT/001/0001, dated 22 September 2000.
58 Walker, Rohde and Condron (1999).
59 Staff, Australian National Quality Assurance Program (2000), personal communication, 28 July 2000.
60 Kefford, B. (2000), Executive Director, Agriculture, Department of Natural Resources and Environment, correspondence, VT/001/0001, dated 22 September 2000.
61 Allworth, B. (2000), National OJD Operations Co-ordinator, personal communication, 7 June 2000.
62 Benedictus, Verhoeff, Schukken and Hesselink (1999).
63 Allworth, B. (2000), National OJD Operations Co-ordinator, personal communication, 7 June 2000.
64 Klein, P. (2000), Executive Director, Sheepmeat Council of Australia, personal communication, 7 June 2000.
65 Allworth, B. (2000), National OJD Operations Co-ordinator, personal communication, 7 June 2000.
66 White, F. J. (2000), Executive Officer, Livestock Saleyards Association of Victoria, Minutes of Evidence, 7 August 2000.
67 Allworth, B. (2000), National OJD Operations Co-ordinator, personal communication, 7 June 2000.
68 Meat and Livestock Australia (1999), p. 74.
69 Juste (1997).
70 Millar, H. (2000), Acting Chief Veterinary Officer, Department of Natural Resources and Environment, Minutes of Evidence, 7 August 2000.
71 Meat and Livestock Australia (1999), pp. 3, 58.
72 Meat and Livestock Australia (1999), pp. 3, 58.
73 Benedictus, Verhoeff, Schukken, and Hesselink (1999).
74 Britton, A. (2000), Veterinary Service Manager, CSL Ltd, Minutes of Evidence, 24 July 2000.
75 Important especially for sheep used for meat products.
76 Britton, A. (2000), Veterinary Service Manager, CSL Ltd, Minutes of Evidence, 24 July 2000.
77 Prowse, S., Minutes of Evidence, Senate Standing Committee on Regional and Rural Affairs and Transport, Melbourne, 24 July 2000.
78 Wood, P. (2000), Research and Development Manager, CSL Ltd, Minutes of Evidence, 24 July 2000.
79 National Johne's Disease Program (1998), Standard Definitions and Rules - Ovine Johne's Disease.
80 Kefford, B. (2000), Executive Director, Agriculture, Department of Natural Resources and Environment, Minutes of Evidence, 7 August 2000.
81 Allworth, B. (2000), National OJD Operations Co-ordinator, personal communication, 7 June 2000.
82 For example, Kefford, B. (2000), Executive Director, Agriculture, Department of Natural Resources and Environment, Minutes of Evidence, 7 August 2000.
83 Prowse (2000), p. 31.
84 For example, Benedictus, Verhoeff, Schukken and Hesselink (1999).
85 Chaitaweesub, Abbott, Wittington and Marshall (1999).
86 Denholm, L. (2000), NSW Agriculture, personal communication, 8 June 2000.
87 CSIRO (2000).
88 Chaitaweesub, Abbott, Wittington and Marshall (1999); and also Webb Ware, D. (2000), personal communication, 13 June 2000.
89 Chaitaweesub, Abbott, Wittington and Marshall (1999)
90 NSW Agriculture (1997b).
91 Nicholls, M. (2000), Co-Chair, NSW OJD Advisory Committee, personal communication, 2 July 2000.
92 Allworth and Kennedy (1999).
93 NSW Agriculture (1999c); and also Button, C. (2000), Acting Senior Veterinary Officer, Maffra, Department of Natural Resources and Environment. personal communication, 16 May 2000.
94 Inspection tours were undertaken of the Tambo Valley and Yarram districts.
95 Gibbins, M. (2000), Secretary, Victorian Stud Merino Sheepbreeders' Association, Written Submissions, OJD074.
96 Balderstone, E. (2000), Minutes of Evidence, 18 May 2000.
97 Webb Ware, D. (2000), personal communication, 13 June 2000.
98 White, F. J. (2000), Executive Officer, Livestock Saleyards Association of Victoria, Minutes of Evidence, 24 July 2000; and also Barrett, B. (2000), Written Submissions, OJD034.
99 White, F. J. (2000), Executive Officer, Livestock Saleyards Association of Victoria, Minutes of Evidence, 24 July 2000.
100 NSW Agriculture (1997c).
101 Dupe, B. J. (2000), Minutes of Evidence, 14 June 2000.
102 Chaitaweesub, Abbott, Wittington and Marshall (1999); and also NSW Agriculture (1997c).
103 Inspection of OJD control in southern NSW, July 2000.
104 NSW Agriculture (1997c).
105 NSW Agriculture (1997c).
106 Prowse, S. (2000), Program Manager, Infectious Diseases and Food Safety, Animal Health Laboratories, CSIRO, Minutes of Evidence, 24 July 2000.
107 Simpson, G. (2000), District Veterinarian with the NSW Central Tablelands Rural lands Protection Board, personal communication, 3 July 2000; and also Denholm, L. (2000), NSW Agriculture, personal communication, 8 July 2000.
108 In particular Colbey, P. (2000), Written Submissions, OJD031.
109 Sykes, W. (2000), Animal Health and Research Consultant, Minutes of Evidence, 24 July 2000.
110 Juste (1997), and also Fridriksdottir, Gunnarsson, Sigurdarson and Gudmundsdottir (1999) and Abbott (2000), pp. 5-10.
111 Fridriksdottir, Gunnarsson, Sigurdarson and Gudmundsdottir (1999).
112 Johne's Information Centre (1997a).
113 Hermon-Taylor (1999).
114 Simpson, G. (2000), District Veterinarian with the NSW Central Tablelands Rural lands Protection Board, personal communication, 3 July 2000.
115 For example, Lawson, D. (2000), Minutes of Evidence, 8 June 2000.
116 Pemberton, D. H. (2000), Written Submissions, OJD 042.
117 Andrewartha, R. (1999), quoted in Meat and Livestock Australia (1999), p. 28.
118 Prowse (2000), p. 29.
119 NSW Agriculture (1997b).
120 NSW Agriculture (1997c); and also Meat and Livestock Australia (1999), p. 13;
121 Richardson, J. and J. (2000), Written Submissions, OJD102; and also Surviving Ovine Johne's Disease, a video produced by NSW Agriculture, March 1999.
122 Department of Natural Resources and Environment (1995), p. 6.5.10.
123 Department of Natural Resources and Environment (1995), p. 6.5.10.
124 NSW Agriculture (1997b).
125 For example, Palmateer Pastoral Co. (2000), Written Submissions, OJD 064; and also Ryan, G. W. and B. J. (2000), Written Submissions, OJD099 and Anderson, W. J. and P. E. (2000), Written Submissions, OJD100.
126 For example, Vickers, B. (2000), farmer, Carcoar, NSW, obtained replacement sheep from New England; also NSW Agriculture (1997c); and also Vickers, B. (2000), farmer, Carcoar, NSW, personal communication, 3 July 2000.
127 NSW Agriculture (1997b).
128 For example Vallance, J. and V. (2000), Written Submissions, OJD 078
129 Prowse (2000), p. 29; and also Australian Animal Health Council Ltd. (2000b) and Kennedy and Harkin (1998).
130 Pemberton, D. H. (2000), Written Submissions, OJD 042.
131 Pemberton, D. H. (2000), Written Submissions, OJD 042
132 Allworth. B. (2000), National OJD Operations Co-ordinator, personal communication, 7 June 2000.
133 Gibbins, M. (2000), Secretary, Victorian Stud Merino Sheepbreeders' Association, Written Submissions, OJD 074; and also Denholm, L. (2000), NSW Agriculture, personal communication, 8 June 2000.
134 Allworth, B. (2000), National OJD Operations Co-ordinator, personal communication, 7 June 2000.
135 NSW Agriculture (1997c).
136 NSW Agriculture (1997c).
137 Denholm, L. (2000), NSW Agriculture, personal communication, 8 June 2000.
