Johnes – is your herd affected?

Hot on the heels of last week’s meeting at The Shireburn Arms, this meeting organised by Myerscough Vets in association with Myerscough College focussed on Johnes disease. Twenty six farmers turned out to hear the speaker for the evening - the ever-popular and entertaining Dai Grove White from the University of Liverpool.

The disease

Johnes is a contagious bacterial disease of the gut which is chronic and long-term. Infection is picked up at birth, or very shortly after, before the immune system has developed. Typically symptoms are seen in older cattle as the incubation period of the bacteria is 3-7 years long. Johnes cannot be treated and once infected there is no chance of the animal ever recovering, hence the only way in which the impact of the disease can be reduced is to control the risk.

Symptoms

A cow clinically infected with Johnes will show a marked weight loss, reduction in milk yield and scours. However clinical cases only make up a fraction (5-10%) of the actual infection level in the herd – for every case you actually see and diagnose there is likely to be at least 10-20 other cows in the herd which are affected sub-clinically.  These cows are often culled for other reasons such as fertility problems, lameness and mastitis before clinical signs of Johnes are even recognised.

Economic effects

• Reduced milk yields – research has shown that a Johnes positive cow may yield up to 4,000kg less milk over a lifetime than a Johnes negative cow.
• Increased likelihood of lameness by five times.
• Cows twice as likely to develop mastitis/SCC problems
• Increased risk of other problems such as displaced abomasums, downer cows etc. due to the fact that Johnes infection will predispose the cow to picking up other infections.
• Overall reduction in farm profits due to increased costs and increased losses from the herd.

The economic effect can be so devastating that Dai has heard of cases where dairy farms have actually gone out of business as a direct result of Johnes disease.

What is the likelihood of Johnes in your herd?

50% of UK dairy herd are infected with Johnes.

This is dependent on two factors:

1)      Bio security – the risk of Johnes entering your herd

2)      Bio containment – the risk of Johnes spreading within your herd.

Bio security

Far and away the greatest risk of introducing Johnes to your herd is through the purchase of infected cattle from other farms. If you have introduced cows into your herd in the past 10 years there is a very strong chance that you will also have introduced Johnes – by introducing just 40 cows over the last 10 years there is a 65% chance that at least 1 of them will have Johnes. The risk increases with increased numbers of bought-in cattle and the prevalence of infection within these herds.

To reduce these risks try wherever possible to avoid buying in. However if this is not an option on your farm then purchase cows wisely from sources that you know have low prevalence.

Other sources of infection can include:

• Imported slurry from other farms
• Drinking water in streams and rivers that is contaminated with faeces from neighbouring farms.
• Sheep and rabbits.

Bio containment

There are 3 main routes by which infection can be transmitted:

• Faecal contamination of calves, udders and the environment – the oreo-faecal route is the most common route of infection. Dai memorably refers to this as the sim (s**t in mouth) method.
• Infected milk and colostrum
• In-utero infection (only 10-20%)

As the cow increases in age she becomes much more resilient to Johnes – 80% of infection occurs in the first four weeks, and more often than not the first few hours, of a calf’s life as the immune system has not developed.

Protect your calves

In order to have any sort of control over the spread of Johnes it is essential that the baby calf is protected and kept away from sources of contamination at birth. One cow can produce up to 50kg of manure every day.

If this cow is Johnes infectious the bacteria will be passed out in her faeces and if the calf comes into contact with any faecal matter, either from a dirty teat, bedding or just being mucked on, he/she will almost certainly become infected.

One ‘super-shedder’ is capable of infecting 50,000 calves in only one day with the amount of bacteria being passed out!

Detecting Johnes

As Dai mentioned previously many cows are culled for another reason before the symptoms of clinical Johnes are ever seen, and so the absence of clinical signs in your herd is not a good indicator of disease freedom.

There are a number of tests which can be carried out, however it must be remembered that not all tests are that accurate and it also depends on the stage of the disease as to whether the test will detect its presence.

-  The gold standard of tests is faecal culture but this test is expensive and time consuming.

-  Blood testing can be used to detect Johnes antibody in the blood which will indicate that a cow is infected and infectious. However the cow will only start producing antibody in the later stages of infection once the bacterial numbers have started to multiply.

-  Similar to blood testing milk testing can be used to detect antibody in the milk.

A one-off test will not be sufficient to determine the true extent of Johnes in a herd – the best reliability will be gained by carrying our regular individual blood screens of the all the cows in the herd. It is pointless testing any stock under the age of 2 years old as they will have insufficient levels of antibody in the blood to gain a response.

Targeted sampling of a proportion of cows in the herd is a cheaper way of detecting infection in the herd, although without testing the whole herd it is impossible to determine all of the individuals that are actually infected. Usually a 30 cow sample is done, with the testing being targeted towards those cows that have the greatest risk of being infected e.g. poor fertility, low yields, and older cows. Even if tests from the 30 cows come back as negative it is worth keeping a look out, particularly if the risks of Johnes entering the herd are high.

What to do next?

Uninfected herds – although 50% of UK herds are infected by Johnes it must be remembered that the other 50% are currently clear. If you are lucky enough to be in this situation you cannot be complacent – Johnes-free herds must do everything they can to stay free.

Protect your herd by:

1)      Sensible and practical bio security measures

2)      Staying closed wherever possible

3)      If buying in ensure you buy wisely from herds that are free or have low prevalence

4)      Continue to monitor herd status

5)      Screen any high risk cows on a regular basis

Infected herds – if your herd is infected there are a number of strategies that can be used to control and manage the risk, however it is very important that you work with your vet in developing a strategy specific to your own farm as each case is individual.

1)      Improved farm management – by testing and identifying infected/infectious cows these can then be managed differently from the rest of the herd at calving, which is the time when infection occurs.

• These cows can be marked, perhaps with a red tag, and then calved in a separate area (leper colony) where they pose no threat to calves being born to uninfected mothers. Any heifer calves born to these mothers should also be red tagged at birth and managed as an infected cow in the future.

• The calving pen should be kept as clean as possible at all times to risk the risk of transmission to new-born calves. If possible each cow should have a separate calving pen which should ideally be fully cleansed and disinfected before the next cow is brought in.
• The risk of transmission from mother to calf can also be reduced by snatch calving whereby the calf is taken away from the cow as soon as is practically possible after birth.

2)      Colostrum is another route of transmission. Calves should never be fed on pooled colostrum as infection from just one cow can be passed onto a large number of calves very quickly. A calf should only receive its own mother’s colostrum (provided she is not infected with Johnes) and then milk replacer after this.

3)      Breeding of infected cows to beef calves is another option as these calves will most likely be slaughtered before their performance is affected by Johnes infection. However care must be taken that any beef heifer calves are not retained as suckler cows.

4)      Vaccination against Johnes is possible, however it must be remembered that any vaccinated stock are likely to fail their TB test. Vaccination in the first couple of weeks of life will help to kick start the immune system of the calf and reduce the severity of the disease if the calf becomes infected – it will not prevent infection.

Whatever methods of control are used by the individual farm they must be realistic for that unit – it is no good saying that all calves will be removed from their mothers within an hour of birth if this cannot be realistically achieved 24 hours a day 7 days a week. It is also essential that the expectations are kept realistic when developing a control strategy – it is pointless aiming for complete eradication within two years as Johnes is a very complicated disease and it is highly unlikely that this will be achieved!

Funded help available

Dai closed with a mention of the funding available through the RDPE Northwest Livestock Programme to help farmers with Johnes control on their farms.

By signing up for an Animal Health Plan (contact SAC directly on 08456 040 535 or view further details on the animal health planning page of this website) it entitles you to up to £250 of veterinary testing as well as a day of veterinary time. The plan involves a farm visit to assess the risk of Johnes and then this information is entered into My Healthy Herd (a web based herd health management programme) along with the results of any blood tests/milk samples to determine your disease status.

Your vet will then work with you to develop a control strategy for your own farm. It is important that you work with your vet as the wrong control policy for your farm can be disastrous.

Further information on Johnes...

Kite Consulting Update >> 

Adas >>

(Pictures on this page courtesy of Peter Orpin, www.MyHealthyHerd.com)

Add a Comment

If you would like to leave a comment, please login or register for an account.