PCHS NEWS. When do we pool samples for testing? August When do we pool samples for testing? 1

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1 PCHS NEWS August 2014 When do we pool samples for testing? There is a constant drive to simplify testing procedures and to reduce the costs of testing. However for some diseases the best test is the most expensive test. That is the case for BVD virus detection where PCR is used to detect the genetic material of the virus. This test is able to detect the virus when it is present in very low numbers. The best example is the use of the test with bulk milk. The test we use has been validated for the detection of one virus positive animal amongst 300 cows contributing to the bulk tank. Clearly if you get a positive result you then have to find a way of testing cows individually to detect the virus carriers, but a negative result provides a particularly cost effective exercise. So in testing terminology a pool is the process of combining more than one sample together to reduce the number of tests carried out. It works best in situations where test positive animals are expected to account for a very small number of the animals tested and where the test is for detecting the organism that causes the disease. The BVD PCR test can also be used in pooled blood or tissue samples. Here the size of the pool is limited by the number of individual tests that require to be done if there is a positive pool. Based on our expected level of BVD virus positive animals at less than 1% we have settled on a pool size of ten as providing the highest efficiency. The test is charged out as an individual test cost produced from the average of all our tests carried out in this screen. Hence you pay the same for identifying the individual virus carrier animals as you do when your herd test is negative. As we progress with BVD eradication the number of expected virus carriers will fall and we will be able to increase the number of animals that make up a pool and reduce our test costs further. When do we pool samples for testing? 1 The date for your TB test has been moved - do you need to move your health scheme herd test date? 2 Johne s suspended status - clarification - effect on sales 2 Why PCHS uses the best PCR test for Johne s 2 Rules for culling - positive, inconclusive, suspicious 3 Where can we find out the health status of cattle from other farms? 3 Can you tell if IBR marker vaccinated animals are a risk? 3 Johne s inconclusive and suspicious animals what is the risk? 4 Bulk Milk Monitoring 4 Bulk tank BVD positive for antibody to BVD: Steps to accreditation 5 IBR: Is buying from a mixed status sale a risk? 6 BVD virus testing in vaccinated herds 6 Neospora control and accreditation 7 Submission of PCHS Samples: What we require 7 BVD Tag & Test Find a Deal 8 Leptospirosis Can my herd become Accredited Free? 8 Are sheep a risk to my cattle herd? 8 Premium Cattle Health Scheme, Greycrook St Boswells, Roxburghshire, TD6 OEQ T: pchs1@btconnect.com Editor - ian.pritchard@sac.co.uk SRUC 2014 SAC Consulting is a division of SRUC SRUC is a charity registered in Scotland, No. SC00371

2 The date for your TB test has been moved - do you need to move your health scheme herd test date? Combining your annual herd test with the herd TB test makes sense; it reduces the number of times the animals need to be handled and it can help reduce the cost of the blood sampling. However what do you do if the date of your TB test is moved? What if the TB test is moved earlier? For herds at Johne s disease risk level 1 then aligning the two tests will not make any difference and the herd will retain its status if the test is clear. The same is true for IBR and for L Hardjo Accredited Free herd tests. For herds that are Johne s disease risk level 3 or 4 the problem occurs if there is a clear test. This cannot count towards accreditation because the test has occurred within 12 months of herd test with positives. It would only be at the following test that status could be changed. The same will not arise for IBR or L Hardjo, because the qualifying test for accreditation may be carried out at an interval of less than one year. What if the TB test is moved later? This is acceptable where the movement is up to one month, but where it is longer than this then things are more difficult. The simplest way is to make sure that all animals that leave the herd during the period from when the test was due to when it is to be carried out should be blood sampled and tested. For herds in the Johne s disease programme both blood and faeces samples should be collected to allow faecal screening if the blood is positive. But most importantly if you are concerned about the implication that this may have on your herd status please phone our office to discuss as soon as you know your TB test date has been changed. Johne s suspended status - clarification - effect on sales It is important to consider the best time of the year to schedule your herd test. In herds that are controlling Johne s disease (risk levels 3 and 4) the priority should be to carry out the test at around two months before calving to allow test positives to be removed from amongst the negative animals before calving. The second consideration is the date of the main sale for your herd and to carry out testing so that any follow up testing has been completed to allow you to publish your accreditation status in the sale catalogue. Ideally this should not be sooner than three months before the date the sales catalogues are compiled. Why PCHS uses the best PCR test for Johne s Testing for Johne s disease is the most problematic of the diseases in the PCHS programme and we need a very good second test to follow up blood test positive results. We do this using faeces to detect those animals that are shedding the organism. We carried out an extensive review of the methods available and we have selected the best commercial PCR test for this. We run this test once a week and the process takes around two days to complete. The problem we have is that although CHeCS accepts the test, our extensive studies have shown PCR to be inferior to the culture system where the sample is grown for six weeks and then we screen the culture fluid by PCR. Our recommendation therefore is to screen by faecal culture and not to rely on direct PCR, despite the convenience of the latter. August

3 Rules for culling - positive, inconclusive, suspicious CHeCS programmes are clear on the definition of reactors. They are animals that test positive by the initial blood test at the herd test or quarantine test. Of course false positives occur with all tests usually at the rate of one or two per 100 of test positives. For this reason there is the option for second tests and for all but L Hardjo we have second test options. Animals that test negative in the second test are by the definition of the programmes no longer reactors. We also have categories of results below the positive cut-off. These are not recognised within the CHeCS programmes, but when we have animals testing in these zones (inconclusive or suspicious) we will recommend that they are retested within a set period of time. Some of the animals may be in the process of becoming positive and the retest will pick this up. For those that are not then the second test offers reassurance that the animals are not infected. We do not recommend that animals that test in the inconclusive or suspicious zones are removed from the herd before further testing is carried out. Where can we find out the health status of cattle from other farms? The Premium Cattle Health Scheme Members Database contains details of PCHS members health status, arranged by seller, area and breed. Go to Google and enter - then PCHS Members Data base then PCHS Members Health Scheme (by seller) or (by area) or (by breed) You then have contact information along with current known status for BVD, Johne s, Lepto and IBR. If you are looking for bulls or females of any breed or maybe sourcing cross-bred recipients the website is worth a visit. Can you tell if IBR marker vaccinated animals are a risk? Either conventional or marker vaccines can be used to protect cattle against IBR. If animals are vaccinated using a conventional vaccine they will test positive for antibody to IBR, even if they have not been exposed to natural infection. Laboratories can however use a different blood test on samples from cattle that have been vaccinated with a marker vaccine. This allows laboratories to tell if marker vaccinated animals have been exposed to natural infection. Animals that have been vaccinated with the marker vaccine and neither naturally exposed to IBR nor vaccinated with conventional vaccine will test negative by this test. Animals that have been exposed to IBR (or vaccinated with a conventional vaccine) will test positive using this test. It is important to know if animals have been exposed to IBR because they will remain infected for life. Infected animals are therefore a source of infection to the rest of the herd and can spread virus particularly at times of stress. August

4 Johne s inconclusive and suspicious animals what is the risk? We carried out a review of the Johne s blood test results from PCHS herds to investigate what happens to the status of these animals over time. The findings indicate that nearly one in two of the cattle (44%) that tested as inconclusive for antibody to Johne s disease, in the blood test that we use, will later test as antibody positive for Johne s disease. Our advice for dealing with inconclusive animals (blood test result 60-70%) is that they should be re-sampled. We previously advised that this should be done after a month however from a review of the retest results it would appear that the optimal time for retesting would be after two months. The best time to carry out the annual Johne s herd test is at least a few months pre-calving so that positive animals can be separated from the herd. This will reduce the exposure of the young calves to the Johne s organism in the dung of infected animals. Shedding of Johne s organisms in faeces starts in small amounts and intermittently whilst the animals still appear healthy. Infected cattle will usually be shedding Johne s in small amounts in their faeces before they become positive in the blood test. As inconclusive animals could be in the process of becoming positive then either retest them at least two weeks pre-calving or else separate them from the calving group and young calves and retest them after calving. Bulk Milk Monitoring Bulk milk offers a ready sample to monitor for antibody to disease. If antibody is present in the bulk milk it shows that animals in the herd have been vaccinated or exposed to the infection in the past. It is extremely useful for those diseases that tend to spread rapidly through the herd leaving a significant number of animals that have been infected and have antibody. The downside is that animals can remain positive for antibody for several years and so a positive bulk milk result only means that exposure to infection or vaccination has occurred at some time and it may have been several years ago. Bulk milk antibody testing works best for diseases such as IBR, BVD and L Hardjo. They work best for monitoring herds that have never had the infection and regular testing monthly or quarterly should be carried out. They are not so good for diseases where relatively small numbers of the cows are likely to be positive at any one time such as Johne s and Neospora. Consider targeted sampling as a look see or monitoring system for these diseases. Bulk milk can also be used to find out whether or not there are any of the milking herd carrying BVD virus (PI animals). Dairy farmers should make sure they are making the most of bulk milk testing. The suspicious category for Johne s blood results is one that we introduced to flag up animals that are worth monitoring as they could be in the process of becoming positive. Our advice with suspicious animals (blood test 50-60%) is to retest them three to six months later. From reviewing our PCHS Johne s blood test results we found that 1 in 4 cattle that initially tested as suspicious were found to be positive at a later date. In some cases this was a few years later. If unsure what action to take following a herd test then discuss the results with your PCHS vet. September August

5 Bulk tank BVD positive for antibody to BVD: Steps to accreditation As discussed above many dairy herds can be expected to have a bulk tank milk sample that is consistently positive for antibody to BVD. This may indicate that BVD is a problem right now or it may mean that it has been a problem several years ago. But if your bulk tank sample is positive for antibody what steps should you take to make sure that BVD is under control? Option 1, bulk tank virus screen: The bulk tank can be screened by PCR for the presence of BVD virus. A negative result shows that at the time of sampling no virus carrier contributed to the bulk tank. Cows that were dry or where the milk was withheld are not tested in this way and so separate sampling of these animals or repeating the bulk milk test after a further three months is required. Option 2, first lactation screen: You can test a composite sample of milk from all the first lactation animals in the herd. This can be easily done at milk recording by combining a sample from each animal into one large container and then sampling from that as if it were the bulk tank. (CHeCS document suggests that samples should be submitted individually and combined at the testing laboratory). If this is negative for antibody to BVD then it means that this age group have not met the infection and that BVD is not currently active in the herd. You can use this test to monitor the herd every three months. If the herd is vaccinated then antibody will be present, but with the vaccines we have available the level of antibody is low. Again monitoring every three months will make this clear. Option 3, heifer check test: You can carry out check tests in your heifer groups before they are vaccinated against BVD. Heifer groups tested in this way should be at least nine months of age and you should blood sample five from each group. If all are negative then there is no BVD virus carrier in the group. Option 4, individual calf virus test: For flying herds the best way is to test all calves born using ear tissue testing as they are tagged. If you find a virus positive calf then you can have its mother tested for virus. You will also be able to sell calves as having been tested negative for BVD virus. If the goal is to be accredited free from BVD then use option 2 quarterly and option 3 as each heifer group reaches nine months of age. If the goal is to be milk monitored free then use option 2 each quarter. If the test results in options 1 to 4 show that BVD is active in the herd then screening of animals to find those persistently infected should be carried out with your vet. And if your bulk tank is negative for BVD antibody you can opt either for milk monitoring free (by testing quarterly) or step up to accredited level by adding in option 3. August

6 IBR: Is buying from a mixed status sale a risk? When cattle pass through a mixed status sale they could acquire IBR infection. Animals infected with IBR remain infected for life. During periods of stress, e.g. mixing or transporting animals, infected animals can shed virus and pass it on to naïve IBR free animals. These animals in turn become infected for the remainder of their life and could be a source of infection if brought into another naïve herd. If a herd is accredited free of IBR it is important to consider all animals passing through mixed status sales as non-accredited, regardless of the status of their farm of origin. These animals should be quarantined and blood tested for antibodies to IBR. This can be done on entry into quarantine to identify positive animals as soon as possible. In addition they must be tested at least 28 days after entry into quarantine. This is because there can be a delay of a few weeks between animals becoming infected with IBR and antibodies being detected in their blood. Bought in animals can only join the herd if they test negative. When a group of animals is bought in and both negative and positive animals are identified; the negative animals must remain in quarantine and be re-tested 28 days after the removal of the positive animals. BVD virus testing in vaccinated herds Many herds use BVD vaccines and these can play an important part in a herd s biosecurity as well as in the control of disease. The use of vaccine doesn t prevent herds from screening for BVD virus as persistently infected animals can still be identified and check tests can still be carried out on young stock. In most cases the breeding herd would be vaccinated to reduce the adverse effects on fertility and help reduce the risk of PI animals being created if there is active BVD virus infection in the herd or in case infection gets into a clear herd. There are also respiratory vaccines available which have a BVD component as infection with BVD virus can cause immunosuppression and therefore worsen outbreaks of pneumonia. If young stock have had one of these vaccines containing BVD virus then the annual check test should be left until at least three months after the vaccination course has been completed. This is because the antibodies from the vaccine can be detected in the blood test which would result in a failed check test. Any antibody positive animals would need to be retested at a later date to prove that the results were just due to vaccination and not due to infection following exposure to the virus. If the breeding herd has been vaccinated against BVD virus or if the breeding females have had previous exposure to BVD virus then the dams would usually have antibodies to BVD virus in their colostrum. These pass across the gut and into the calf s blood stream in the first 24 hours of life. They remain in the blood for months but wane over this time. By the time the calf reaches four to six months old these antibodies will usually be very low or may no longer be detectable. However in some calves the maternally derived antibody can persist for longer, even up to nine months old. This is the reason that check tests should be carried out on young stock once they are over nine months old so that the maternally derived antibodies do not interfere with the interpretation of the results. If calves are sold before they reach nine months old then the annual check test can be done when the calves are 6-9 months old however if this is the case then ten need to be sampled per group. Any calves that test as antibody positive would need to be retested to prove that the antibodies were due to colostrum and not from natural infection. If all calves are sold at weaning and can t be tested when they are 6-9 months old then all calves born into the herd each year would need to be tested for BVD virus (antigen) to identify if any PI animals have been born. This can be done using blood samples or ear tissue. If unsure as to which BVD screening option is appropriate for your herd discuss it with your vet or contact the PCHS office for advice. August

7 Neospora control and accreditation Neospora caninum, to give its full name, is a parasite of cattle similar to Toxoplasma in sheep. And, like Toxoplasma, infection can result in death of the developing foetus and abortion. Neospora infection is passed from dam to the developing calf in the womb and infected females are more likely to suffer abortion than those that are not infected. However not all calves that become infected show ill effects. The parasite is found as a tissue cyst in the placenta and aborted or stillborn calf. If this material is eaten by dogs they can under go a cycle of infection that results in the infectious stages for cattle being passed in their faeces. Female cattle can then become infected if they consume feedstuff contaminated with dog faeces. It must be emphasised that dogs will not become infected without exposure to abortion material and that the most important cycle of infection is from infected dam to calf. We have a blood test that can show if the dam is carrying the infection. Animals that are born infected mostly begin to test positive towards the end of their first pregnancy. Animals that acquire infection by consuming contaminated feedstuffs mostly test positive at the time they abort. This means that it is not a good screening test for purchased heifers. However if the dam of the heifer is negative for antibody then the heifer will be free from infection. Whole herd testing will offer assurance that your herd is not infected and that the female breeding stock you sell are likely to be free from infection. Your herd can become CHeCS accredited Neospora Free. Make sure that all aborted or stillborn calves and all placentas are disposed of in a way that does not allow dogs to scavenge them. The parasite has no effect on the fertility of the bull. Infected bull calves can only lead to new infections if they die and are eaten by dogs, which in relation to UK farming practices is a very unlikely outcome. Submission of PCHS Samples: What we require There is nothing worse than receiving a set of samples from a herd test that are in a filthy condition. The biggest problem with this is that the details on the tubes and paperwork can be difficult or impossible to read and even barcodes on the tubes may not scan. There is also the issue of contamination and the risk of infection to anybody handling samples that have been contaminated with cattle faeces. The following is our guide to provide you with the best outcome. Blood Samples We provide barcoded labels for scheduled routine blood tests and can supply barcodes for any other large test such as a search for PI animals. If you are undertaking testing of a new herd or an additional test of more than 20 animals please contact your PCHS SAC Office to request barcoded labels for the test. On receipt of the samples the tubes are scanned into our system and contaminated tubes often do not scan, increasing the time to process the work and creating the opportunity for error. The labels we supply are waterproof so can be wiped clean prior to submission. Make sure that the label with the barcode runs the length of the tube. It can t be read if it is wrapped around the tube. Faeces Samples It is really difficult to avoid contamination when faeces samples are submitted in inappropriate containers (gloves, jam jars, plastic boxes, etc). From each animal please provide a single, clean, screw top universal container; filled but not overflowing with faeces. Please wipe off any faecal contamination of the container prior to submission. Note that your vet must collect all faeces testing for certification. All samples taken for culture/pcr should be taken using a new uncontaminated glove and taken direct from the animal ( not off the ground) Sample Identification For the occasional sample where we have not given you a barcode please identify blood tubes and faeces samples using a numbering system on the tube/universal container and provide paperwork that lists the number and the corresponding full UK ear number. Please do not attempt to write animal identities on sample containers as this inevitably results in transcription errors. Please ensure 6 and 9 are distinguishable by underlining ie 6 9. Thanks for your cooperation. We use robotics for testing samples and the only tube that fits the robot is a 7ml vaccutainer. As all our testing requires a clotted sample (red top) please submit a full 7ml vaccutainer from each animal. August

8 BVD Tag & Test Find a Deal Many producers use BVD tissue tags to identify PI animal/s in their herds having been alerted to the possible presence of PI through a blood test result showing evidence of exposure to BVD. Identifying a PI and taking it out of the herd at the earliest opportunity is vital and is often done shortly after birth using a tissue tag which can also double as the UK identifier tag if required. SAC PCHS has contracts with various tag companies where we have been able to install automatic tissue tag tube openers. It is also felt that these companies have a robust system for collecting tissue samples. Contracts are already in place with the following companies and clients are advised to contact the companies. Caisley Eartag Ltd Cox Agri Toptag ID Systems Ltd Ketchum Leptospirosis Can my herd become Accredited Free? The qualifying test for leptospirosis is performed on blood samples from eligible animals. Eligible animals are all cattle in the herd over two years of age plus those aged between one and two years that are intended for breeding. These samples are tested for antibodies to Leptospira Hardjo. A positive result can arise from either genuine exposure to L. Hardjo or from vaccination against the organism. Our testing cannot tell the difference between the two. If a small number of positive animals are found, the herd can still work towards accreditation. This may be appropriate if for example the herd vaccinated in the past or have bought in positive animals. In this situation it may be appropriate to initially enter the L. Hardjo Monitored Free Programme. This programme allows for up to 5% of eligible animals to test positive. The herd would be declared Monitored Free if at the second qualifying test, twelve months later, no further test positives are identified. Previous test positives do not need resampled. It is important however to also screen any sick animals and those that abort or produce stillborn calves for leptospirosis. The Monitored Free status is maintained by ensuring no further test positives are identified on annual testing. In time herds may wish to removed test positives from the herd and enter the Accredited Free Programme. A herd is declared Accredited Free when two qualifying tests are performed between six and twelve months apart and all eligible animals test negative for antibodies to L. Hardjo. Are sheep a risk to my cattle herd? Sheep can carry Johne s disease and are a potential infection risk to cattle herds. Risk can be minimised by never co-grazing cattle and sheep and avoiding grazing cattle and sheep on the same pasture in the same year if at all possible. To monitor Johne s infection in sheep flocks it is possible to test a pooled sample prepared from faeces from up to ten sheep. The candidates for testing should be selected on the basis of being thin without any other disease which would explain the poor condition (e.g bad feet, broken mouthed). Dung samples should be submitted in individual containers to be pooled at the laboratory. Demonstrating freedom from Johne s disease in the sheep flock is a recommended component of health planning for a Risk Level 1 cattle herd managed alongside a sheep flock. A positive result in the sheep flock will not result in loss of status in the cattle herd but could provide vital information when making health planning decisions for both enterprises on the farm. August