Managing and treating Johnes webinar questions and answers

The questions and answers from our webinar looking at the practical strategies for reducing Johne's with Arthur Owen from our strategic dairy farm Bodysgaw Isa and Karen Bond, Veterinary Technical Advisor at National Milk Records.

• Can an adult cow that is clear of Johnes get infected?
  • Yes, cows are still able to be infected as adults but it takes a much larger infectious dose and they would likely have left the herd before they show signs. It is still a good reason to get rid of heavy shedders though to reduce environmental contamination.

• Is stress also the trigger to go from stage 2 to stage 3?
  • We believe so but the research is very hard to do. It is also likely to be in part down to the infectious dose they received.  The higher the dose; the earlier they are likely to succumb to the infection and enter stage 3.  Also the greater the stress/ more periods of stress the earlier they are likely to succumb.  Remember this can be physical stress, nutritional stress or disease.

• Could you test all adults at 2 years despite calving status?
  • You can test animals at any age using blood/faecal sampling, regardless of whether they have calved or not. The two years is rather arbitrary but correlates to first calving.

• Is Johne's as prevalent in beef suckler herds are we just pushing the problem to them?
  • Johne’s is prevalent in beef sucklers and seems especially so in some breeds. It is a slightly different risk profile in beef herds and they tend to have fewer ‘explosions’ of disease.  The pattern is much more dam:daughter (1:1) and so it can be a problem but often doesn’t get too out of hand.  The problem in beef herds tends to be exacerbated if they calve en masse indoors rather than at grass.  Breeding Johne’s positive dairy cows to a beef sire is an effective strategy for Johne’s control in the dairy herd but yes, potentially causes a problem for the beef industry if those offspring don’t go for slaughter and end up as the suckler cows of the future.  Buyers of dairy cross suckler cows should be aware of this and ask the right questions before purchase.

• Would you do a milk test on stored/frozen colostrum? Or do you dump all Johnes affected cow colostrum
  • You could test colostrum for the MAP bacteria but it is difficult and expensive. I would advocate disposing of all colostrum from known Johne’s cows.  Labelling of frozen colostrum is really important so that should a cow become positive you can go back and remove any of her colostrum from your store.  Also worth noting that freezing does not kill MAP.

• How much does a blood test per cow cost the farmer for Johnes?
  • Speak to your vet as this may vary depending on the lab they use and their sampling costs.

• Karen, if an animal comes back as positive on the antibody test, is it likely to be shedding currently? Or is there a delay/lag between shedding and AB response?
  • Very difficult to answer definitively but this is what we know. Antibody production is triggered by the bacteria emerging and multiplying so shedding happens prior to detectable antibody production, likely by a minimum of 2-3 weeks.  If the cow is now antibody positive we don’t know if she is still shedding or whether it has stopped and we are seeing ‘historic’ antibodies.  So, if she’s antibody positive we know she has been shedding recently but can’t say if she still is right now.

• Are there any particular disinfectants to use in the calving areas or calf sheds that destroy Johnes bacteria?
  • Any disinfectant that has a claim to kill TB will be effective against MAP eg Virkon/FAM. Make sure you follow the manufacturers instructions and use the correct dilution rate.

• What are Karens thoughts on pasteurising colostrum?
  • There is good evidence that it is effective in killing MAP if used at 60^oc for 60 minutes, however it only provides a log reduction in the number of MAP present; so make sure that what you are putting in the pasteuriser isn’t grossly contaminated to begin with! If you start with 100 bacteria you finish with 0 but if you start with 10 million you’ll still have thousands at the end!  Hygienic harvesting is key.  Also remember this is just one part of Johne’s control, it helps but as adjunct to other management.

• What should I do if a cow turns positive during pregnancy - with her calf?
  • Ideally that calf should be reared for beef, but it is always your best cow in calf to a high genetic merit bull; and the calf is always a heifer! If you really must keep it, snatch the calf at birth as cleanly as possible and feed it colostrum from a low risk cow.  Don’t house it with your ‘green’ calves and make sure you mark it in some way (tag is best) so that you can identify it when it comes to breeding time.  Don’t breed a replacement from her and be on the look out as the calf is at significantly higher risk of being infected.

• What about injecting the newborn calf with specially prepared antibody to the Johne's bacterium ? The idea being to extinguish any Johne's bacteria that get into the calf
  • The big problem we have is that open gut at birth which allows the bacteria to get in, and once they’re in hiding away it is almost impossible to get them out! The closest we have is the vaccine which tries to make the bacteria stay inside the cells and not cause any trouble.  There is a huge amount of research into this sort of area and something like this is a bit of a holy grail!

• Is that vaccination with antigen or antibody ?
  • Vaccinations are all about giving the animal (or human!) a small dose of the organism (usually killed or attenuated so it can’t reproduce) that will stimulate the immune system to produce antibodies against it so that if the body meets that disease further down the line it already has some defence against it and can fight it off more quickly and effectively. In the case of the Johne’s vaccine it is killed MAP bacteria.  So the vaccine contains antigens that stimulate and antibody response in the recipient.

• Can milk residue from an infected cow contaminate the milk of the next cow being tested in that stall? So potentially having false medium/high cows?
  • There has been a lot of work looking at ‘carryover’ of milk in the sampling protocols. There is likely to be a small amount of residual milk left from the previous cow but provided the sampling is carried out correctly this isn’t be enough to affect the results.  If you are concerned speak to your milk recording organisation and they can discuss the sampling regime on your farm.

• As heifer blood sampling can be expensive, can snatch calving on an ensuring calf is kept clean help reduce risk for calf?
  • Yes, everything you can do to reduce the risk of that calf getting a mouthful of MAP bacteria helps to reduce the risk! Hygiene of calving area, cows and getting the calf away quickly all help.

• Is there a dilution factor in pooled stored colostrum milk as we had one cow come back positive in April even though she had always been clear?
  • There is a dilution factor and it is all a numbers game. The more MAP in there in the first place the higher the risk so hygiene of harvesting and making sure there is no faecal contamination are key.  Pooled colostrum/milk can be a very effective delivery system for MAP to a large number of calves so if you are going to pool then it needs to be done very carefully and with no known Johne’s positives contributing to it.  It is always a risk.  Hopefully that cow that has since gone positive wasn’t shedding when you were using her colostrum.

• If the Antibody test can only pick up when the cow is having a period of under stress/being infectious, despite the higher cost, why not test for the MAP virus itself? Can it pick up a Johnes cow whatever stage she is in?
  • The most common way to test for the MAP bacteria is in faecal samples, but to find it obviously it needs to be there. In most animals faecal shedding is low and intermittent and so the test can be a bit hit and miss.  If you get a positive then you know the cow has Johne’s, if it is negative; maybe she wasn’t shedding that day or maybe the 5 grams of faeces tested out of the 30kg she produced is the bit that doesn’t have any MAP in it?  Antibody testing is used routinely because although not perfect it is relatively cheap and therefore you can repeat it frequently which gets around some of the problems of them not being positive all the time.  There are new tests becoming available that are looking for MAP in white blood cells which could provide us with an earlier diagnosis.

• If you are very keen to try and clear out Johnes as best as you can, should you look at all at the cow that has a result of 29? or multiple high 20s?
  • Once you get down to having very low numbers of positives in your herd then you do start to consider being a bit harsher in your interpretation of the test results and that could include looking at animals with results close to, but not above the cut off. How to do this requires thought on an individual farm basis and some good analysis of results.  Best to discuss this with your Johne’s vet advisor, and only one for those trying to get those last bits of Johne’s out of the herd.

• Karen how long does the bacteria live for in muck and on fields?
  • MAP can survive for up to 55 weeks on pasture and it tends to remain on the grass and in the upper levels of the soil.  It can also survive for 48 weeks in water and sediments and at least 6 months in slurry. Remember that it is your younger animals that are most susceptible so they should be prioritised when it comes to clean grazing.

• Is it safe to take eggs from a johnes cow & put them into a johnes free cow?
  • There is no evidence that eggs or embryos are a risk. The risk comes from the recipient and her ability to infect the calf in utero or at birth if she is Johne’s infected.

• Do the young animals also shed MAP in faeces?
  • There is some evidence for a period of shedding after infection, and it has been demonstrated that infected calves can shed and transmit the infection to pen mates. the quantity and frequency of shedding in young animals is low but it reinforces the need to keep offspring of known Johne’s cows separated from your replacements from birth.

• Are there tests available for young animals potentially in stage 1? is this muck testing or blood testing?
  • See answer to ‘If the antibody test.....’

• Is there evidence of transmission across the placenta?
  • In clinically affected animals (scour/weight loss) the risk of in utero transmission is between 20-40%.  In those animals that are test positive but with no clinical signs the risk is approx 10%.  Remember that the risk of being infected through contact with cow muck is still the biggest risk of infection.

• At what age is a calf no longer considered high risk for infection?
  • Calves under 6 months of age are most susceptible to infection with MAP, with a considerable difference in susceptibility noted between adults, and calves less than 6 months, and between adults, and calves between 6-12 months. The rate of decline of susceptibility with age has a large impact on transmission.  Calves infected at more than 6 months of age are less likely than younger calves to go on to develop Johne’s disease but still have a significantly higher rate of infection than adults. Adults can be infected if exposed to high levels of MAP, such as from a heavily contaminated environment.  From the point of view of epidemiology and onward transmission, this is less significant due to the incubation period as cows infected as adults will likely be culled from the herd before they begin to shed.

• If heifers are blood test pre-calving , do they still need to be milk tested again quarterly
  • The sensitivity of the test in young animals is low and there will likely be peaks and troughs of antibody production through the stages of the disease. This is the same if you are blood or milk testing at any stage.  Repeated testing maximises your chances of picking up one of those peaks and identifying your high risk cows earlier in the course of disease.  Your choice of testing regime should be discussed with your vet.

• How long will the bacteria live in slurry/muck? is there a specific length of time you should leave between grazing and spreading slurry?
  • See question above ‘How long does the bacteria...’

• How specific is the test?
  • The antibody test has a quoted sensitivity of >99% so we would expect fewer than 1 false positive in 100. The predictive value of the test is also strongly influenced by the prevalence of the disease in the herd/ population.

• Karen, how effective is pasteurisation against controlling MAP? is 60 degrees for an hr good enough?
  • See answer above ‘What are Karen’s thoughts...’

• When Johne’s is present in a herd, what percentage of cows would you expect to be infected or does this vary a lot?
  • This varies a lot. we see herds with <1% of cows testing positive up to herds with >25% testing positive and everything in between.  More than 50% of the herds we see quarterly testing will have <5% test positive cows.

• How much does TB testing effect Johnes results
  • Due to the injection of an extract of Mycobacterium Avium (which is closely related to MAP) during the TB skin test we see a sensitisation which can affect the Johne’s antibody test results. This impact is seen for up to 43 days in milk sample and up to 70 days in blood samples so Johne’s testing should be postponed until that time period has elapsed.

• We’ve had cows in 7th 8th lactation test positive after man tests this after collecting colostrum every lactation.
  • Unfortunately due to the nature of the disease hiding away for long periods of time this is something we can see. Animals can go positive on the tests at any point (the oldest I have seen become positive and then succumb to clinical disease was 13 years old!) and when it happens seems to be determined by the infectious dose of MAP they receive and also how stressful their life is.  There is a risk that those calves fed her colostrum in the past could have become infected but provided the colostrum was hygienically harvested the risk is fairly low.  Calves born to those dams may however have been infected from her muck.

• Is there any research work looking into earlier diagnosis...whilst MAP is still in white blood cells?
  • See above question ‘If the antibody test...’

• Are cattle tested from abroad in the same way?
  • The same testing methods are used in most countries across the world but care should be taken as the interpretation of results can be different. When buying cows it is important to take into consideration the testing and management history of the farm of origin, not just the cows being bought (although this is often difficult if buying from abroad).  Always ask to see the numerical results of the tests for the cattle you are buying rather than just a positive /negative status, that way you can work with your vet and look at the results.  Just because you are told that a cow has a negative test result doesn’t mean that their interpretation of ‘negative’ is the same as ours here.

• Can Johnes cows that have a beef calf feed her own calf?
  • Ideally you don’t want to be using colostrum/milk from any know Johne’s infected animal to feed any calves, even if they are not going to be kept as replacements. There are always incidences where an animal you thought would be going to slaughter for beef could end up being kept by someone as a dairy cross suckler for example.  Also it has been known for beef fatteners to go down with clinical Johne’s before they reach slaughter weight and it can certainly impact their growth even if they do not become clinical.

This project has received funding through the Welsh Government Rural Communities - Rural Development Programme 2014-2020, which is funded by the European Agricultural Fund for Rural Development and the Welsh Government.