Scottish Government

Controlling Johne's disease IN DAIRY herds.

Johne's disease or paratuberculosis is widespread in the major dairying areas of the world. It is a difficult disease to control. The disease can have a significant financial impact on herds through loss of output and early culling. There is also concern about the possible human health risks associated with the bacterium that causes Johne's disease, particularly if it is found in milk.

All dairy farmers should prepare and implement a herd health and welfare plan with their veterinary surgeon that includes a policy on the control or prevention of Johne's infection. This guidance provides essential information on Johne's disease and suggests strategies for its control in dairy herds.

Johne's disease - What you should know:

Johne's disease is an infectious wasting condition of cattle and other ruminants caused by Mycobacterium avium subspecies paratuberculosis (more commonly known as MAP). It is closely related to the organism that causes tuberculosis. The disease progressively damages the intestines of affected animals, and in cattle this results in profuse and persistent diarrhoea, severe weight loss and loss of condition and fertility. In dairy herds, the presence of Johne's disease will significantly reduce milk yields well before other symptoms of the disease can be found.

How is MAP spread?

MAP is passed in large numbers in the faeces (dung) of diseased animals. A single diseased animal can therefore pose a high risk to the rest of the herd. Diseased animals may also excrete MAP in milk and colostrum. While cattle remain susceptible to infection throughout life, they are at their most vulnerable in the first few months of life. Calves may be infected in the womb but are more commonly infected through:

• drinking contaminated colostrum;
• ingesting dung that may be present on unclean teats;
• contaminated feed; and
• contaminated environment or water supplies.

The organism is extremely tough and survives for up to a year on pasture, in slurry and in water. Other animals, particularly deer, sheep, goats and South American camelids such as llamas and alpaca can carry MAP and pass it in their dung. They can therefore be sources of infection where there is co-grazing or sequential grazing in the same pasture. Rabbits and other wild life can be infected with MAP, but their role in spread of the disease is unknown.

How can you spot Johne's disease?

MAP is a slow growing organism. After infection, it may be years before the infected animal becomes ill. Signs of the disease are rarely seen before two to three years of age. Generally, there is a period of reduced milk output or fertility well before the animals begin to show profuse diarrhoea. At the early stages of infection, the only way to confirm whether an animal has Johne's disease is to carry out blood tests, but these do not detect all infected animals. Diagnosis of infection in the early stages is difficult. Tests to detect antibody in the blood are more likely to identify infection than tests for the organism itself. The signs of advanced disease are persistent and profuse diarrhoea and significant weight loss. These symptoms are seen most commonly in animals at three to five years of age. At this stage, examination of a dung sample through a microscope is a useful way to confirm the diagnosis.

Johne's disease- a long term problem

When a case of Johne's disease is discovered in a dairy herd, many other animals within the herd will have been exposed to infection. It is very likely that the disease will be developing in several other animals. For every diseased animal that is found in a herd, it is likely there will be a group where the disease is already affecting their milk output or fertility and a group where the disease is taking hold and the effects will be seen in later years. Because of the high persistence of MAP in the environment and the long "silent" period between infection and the first symptoms of disease becoming apparent, it takes a long time to significantly reduce the level of infection in a dairy herd.

Why control Johne's disease?

If uncontrolled, Johne's disease will have a financial impact to your dairy business. Particular impacts include:

1. Milk production may be impaired before other clinical signs are evident, but the loss of production may not be recognised as due to Johne's disease. In the lactation in which signs of the disease become apparent cows can produce 25% less milk than their potential yield. In the lactation before this the reduction is 10%. By the time signs of diarrhoea and wasting are clear, milk yield will be significantly affected. Your total milk yield and thus income from the herd could be significantly decreased.
2. Infected cattle are more susceptible to other diseases such as mastitis and because they have difficulty maintaining body condition their fertility is poor. Treatment of these conditions is expensive, and you will have to consider the costs of replacing culled stock.
3. The capital value of your breeding stock could also be reduced if there is demand for stock or milk from herds that can be certified as tested free of Johne's disease.

Screening your herd for Johne's disease.

Because it takes a long time for the symptoms of Johne's disease to appear in infected cattle, you may not know that it is present in your dairy herd. It is very important to look out for signs of the disease and advisable to take steps to screen the herd for the presence of MAP. This will help you and your veterinary surgeon decide the best course of action, particularly in preparing a herd health and welfare plan.

Once an animal has severe diarrhoea and is losing weight the disease can normally be readily confirmed by a blood test or by microscopical examination of the dung. The MAP organism can be cultured and identified from the dung, but it takes up to six months to obtain the result - too long for this to be useful for the routine diagnosis of disease. However diagnosis of the presence of the organism in animals in the silent period of the infection, before symptoms become apparent, is difficult. Infected cattle seldom pass detectable numbers of MAP in their dung until they are beyond two years of age.

There is a blood test that detects the antibody to MAP produced by infected cattle. However, cattle tend to produce the antibody to MAP relatively late in the infection. In some individuals it may be difficult to confirm the presence of infection in the live animal. Where an infected animal is tested throughout its life it can be expected to test negative on one or more occasions before it tests positive. This also means that testing animals at the point of sale or on arrival in their new herd cannot guarantee prevention of the introduction of infected animals to the herd.

Taking these realities into account, you should, in consultation with your veterinary surgeon, develop a screening programme that best suits your business needs. For instance:

• If you believe your herd is not infected and you wish to provide a high level of assurance for certification to support sales, a regular testing programme may be appropriate. This might take the form of a blood test every one or two years on all or part of the adult herd, combined with tests on any "suspect" animals;

• If you know John's disease is present in your herd and want to try to eradicate it, a more intensive programme will be needed.

Suitable testing programmes are provided by schemes that operate under the guidance of Cattle Health Certification Standards (CHeCS).

Strategies for Controlling Johne's Disease

Whether or not Johne's disease has been detected in your dairy herd, you should implement a number of basic biosecurity measures, incorporated into your herd health and welfare plan. They will help stop the disease being introduced into your herd, and, should it already be present, they will help to prevent its spread to other unaffected cattle.

Stocking

The major source of infection is the purchase of infected dairy or beef cattle or other livestock (including sheep and other species) that are not yet showing the signs of the disease. To keep the disease out of your herd or to prevent re-infection it is preferable to maintain a closed herd. If replacements are essential it is necessary to limit the purchase of replacement breeding stock to herds that are undergoing regular testing and where no evidence of infection has been found. The longer such a herd has regularly tested negative, the lower the risk of purchasing an infected animal. Herd health accredited farms are a possible source of new infection-free stock. If you cannot find a fully tested herd as a source of replacement stock, you should at least ask your veterinary surgeon to discuss the Johne's disease status of the vendor's herd with the vendor's veterinary surgeon.

Clean Water

Johne's disease can spread by contaminated watercourses. You should:

1. Wherever possible, provide mains water for drinking.
2. If you have a private water source, get it checked to ensure it is safe.
3. Ensure that drinking troughs are kept as clean as possible.
4. Where you are able to provide water through a mains supply or a clean private source, fence off your herd's access to streams and rivers, particularly slow moving watercourses or stagnant water that the cattle use for wallowing.
5. If you are grazing in flood meadows, you should try to delay grazing as long as practicable after flooding has occurred and subsided.

Pasture management

MAP may be present in dung or slurry. Because it is a tough and persistent organism, it may be found on pasture for at least a year after slurry or manure has been applied or has been contaminated by grazing cattle. Even if manure has been well composted, MAP may still be present. You should avoid grazing young animals on land for a year after application in order to minimise the likelihood of infection.

Deer, sheep, goats and South American camelids (including llamas and alpaca) are also susceptible to the disease. On farms where the disease is present in cattle it may spread into these animals that will then act as an infection reservoir. Infection could therefore be reintroduced to a herd through these species. You should therefore avoid co-grazing and sequential grazing with these animals in the same grazing season should be avoided.

Protecting calves and young cattle from Johne's disease

An important source of infection of calves is faecal contamination of the milk, teats soiled with dung, or faecal soiling on a calf's coat, which the calf then swallows when grooming itself. It is therefore most important to prevent young animals from being exposed to dung or slurry from adult animals. This begins from the moment the calf is born. You must:

1. Ensure cows calve in clean well-bedded areas. The ideal is calving boxes thoroughly cleaned and disinfected between cows. The dam's teats must be as clean as possible to prevent ingestion of faecal matter.
2. Ensure that calves are subsequently reared in a clean environment, free of adult faecal contamination.
3. Do not graze young stock on pasture where adults have grazed or where slurry has been applied in the past year.

If you have Johne's Disease in your dairy herd

New-born Calves

If Johne's disease has been found in your herd, you must be aware that MAP may be present in the milk of infected cows and is commonly found in their colostrum. When calves are born in such a herd they are particularly vulnerable to infection, and specific measures are necessary to minimise the likelihood of infection occurring.

When calves are born it is important to follow the advice in the Code of Recommendations for the Welfare of Cattle. However, in order to minimise the likelihood of infection you may need to consider removing the calf from its dam earlier than the recommended 12-24 hours after birth. You should seek the advice of your veterinary surgeon in advance of calving to decide when a calf should be removed, and this should be recorded in your herd health and welfare plan. If you must remove calves from their dams early, it is essential that they are subsequently reared in a clean, thoroughly disinfected environment, free of adult faecal contamination.

It is also essential that new-born calves receive sufficient colostrum, so you must ensure that:

• Calves only receive colostrum from their own mother, or in the absence of their own dam's colostrum, preferably only from a single animal that has repeatedly tested negative for MAP.
• After receiving colostrum they are reared on milk replacer or milk that has been sterilised by heating to boiling point.
• Where calves are allowed to remain with their dam, teats must be as clean as possible, to prevent ingestion of faecal matter, and the pen must be kept clean.

DO NOT feed discarded milk to calves unless it has been sterilised by heating to boiling point.

DO NOT pool colostrum and feed to calves. Pooling colostrum from a herd where Johne's disease is present should, if possible, be avoided, even from cows that have tested negative. It cannot be guaranteed that an animal that has tested negative will not be shedding MAP, and pooling colostrum will increase the risk of infecting calves. However, given that pooling colostrum is an important strategy for controlling other diseases, you should seek the advice of your veterinary surgeon, taking into account the particular needs of your herd.

Herd Management

If Johne's disease is confirmed as being present in your herd you should, in consultation with your veterinary surgeon, take the following action:

1. Remove animals that have tested positive from the herd as early as possible. Removal before the animals show clinical symptoms of Johne's disease will minimise the exposure of other animals to the organism as the numbers of the MAP organism shed with dung are relatively low at early stages of infection.
2. As the offspring of infected females have a high chance of being infected these should also be removed from the herd. Do not breed from the offspring of infected animals.
3. Ensure that the general biosecurity measures explained in this guidance note have been put in place to limit the spread of infection in the herd.
4. To prevent re-infection of your herd, it is preferable to maintain a closed herd. If it is essential to buy in new stock, limit the purchase of replacements to herds that are undergoing regular testing and where no evidence of infection has been found. The longer such a herd has regularly tested negative, the lower the risk of purchasing an infected animal. Herd health accredited farms can be a possible source of new infection-free stock.

The Cattle Health Certification Standards body (CHeCS) has defined the industry standard screening and control programme for Johne's disease that provides an agreed mechanism for herds to follow a test and cull programme.