BVD qpcr Bulk Milk Test

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BVD qPCR Bulk Milk Test

NML launches a new method for BVD screening...

NML launched their new bulk milk BVD qPCR service at the BCVA in mid November 2012. The service offers a simple and easy method to detect BVD virus in the bulk tank*.

“Antibody testing on a routine basis is useful for many herds to show if the herd has been exposed to virus”, says NML HealthCheck Manager Steve West, “but we know that vaccine response can make interpretation difficult – so by bringing in a service that can identify and quantify the actual virus, we have a full system that will provide vets with a huge amount of information about the BVD status of a milking herd”.

“This new qPCR service works well in partnership with routine antibody testing of the bulk tank as a first step for routine surveillance of BVD,” says NML consultant vet, Neil Howie, “If you consider the levels of exposure in parallel with the levels of virus in the bulk tank, it provides useful information about the timing of an outbreak and could provide an early warning system”.

“NMLs archived bulk samples can be used for testing so there is no need for additional sampling” says NMLs Vet Services Manager, Chris Spence, “we have also built this into our automatic vet ordering system, Request and Test”.

But don’t forget the youngstock... NML also offers blood antibody testing services for groups of 5-10 prevaccinated youngstock over 6 months of age (in each management group) to identify if animals have been exposed to virus.

An ad hoc bulk milk qPCR test will cost £25 and the quarterly service is offered for £80 per year.

Please find below recommended approaches to bulk milk BVD surveillance on dairy farms and for dairy youngstock or beef herds. More information on this topic can also be found in next month’s cow management.

*sensitivity of the test is up to 300 cows milking into the bulk tank.

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Whole Herd

Milking Portion

Screen bulk milk: Quarterly qPCR Quarterly antibody -ve qPCR -ve antibody -ve qPCR +ve antibody +ve qPCR +ve antibody Naive herd, no excretors by test sample. Some vaccination or natural immunity, no excretors by test sample.

Some vaccination or natural immunity. Some excretors in test sample. Vaccinate Assume natural immunity will develop and infection will die out

Vaccinate

Assume vaccinal immunity will compliment natural and infection will die out

+ve Ab test individual milk or blood -ve Ag test individual tissue or blood +ve Ag -ve Ag retest in 3 wks to check for transient infection +ve Ag PI Slaughter 1 2 3 4 5

A recommended approach to bulk milk

BVD surveillance on the dairy farm

This approach to surveillance of the bulk milk would identify possible sources of virus within the milking herd. It is important to ensure that a suitable youngstock surveillance method is employed in parallel. Furthermore, NML recommends that every surveillance structure is generated according to instruction from the veterinary consultant for the respective holding.

KEY Test selection Interpretation Test result Vaccination Vet input 6 7

For more information about specific test services

please go to www.nationalmilklabs.co.uk

Or contact customer services on 08447 255 567

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1. This herd has some protection from BVD but it id difficult to establish how much. The antibodies may be derived from vaccination or exposure to live virus. On the day of sampling no detectable virus was in the milk, so it is likely that there were no excretors amongst the cows milked that day. There may be infection in the stock that did not contribute to the bulk tank. decisions will have to be made about protecting the herd and ongoing monitoring.

2. This herd has no measurable antibodies to BVD ,and on the day of sampling, no

detectable virus was in the milk. This is likely to be a naive herd. Decisions will have to be made about protection of the herd by rigorous biosecurity and or vaccination. There will be a need for ongoing monitoring.

3. This herd is infected with BVD. On the day of sampling an unknown number of

excretors were milked. Some of the herd are immune, by natural exposure or vaccine. Decisions need to be made about whether to rely on protection of the non infected herd members by natural exposure or vaccine to control risks while viral infection dies out. Alternatively investigations can be made into individual animals’ status regarding infection and immunity.

4. Decisions need to be made in an infected herd about whether to rely on natural

challenge to develop protective immunity, or to use an effective vaccination programme.

5. If it has been decided to pursue an investigation of the herd members' status,

decisions need to be made about testing for antibodies and or antigen. - Antibody positive animals are not Permanently Infected excretors.

- Antibody negative animals may be naive or Permanently Infected. They should be tested for BVD virus antigen.

- Antigen positive animals should be retested, and if repeat positive are likely to be Persistently Infected.

6. Antigen negative animals could be infected between antibody and antigen testing,

and could be resampled for antibody. Alternatively, they could be assumed naive and free of infection and in need of protection.

7. Decisions must be made about antibody positive and antibody negative/antigen

negative animals. Protection from naturally acquired antibodies may be supported by an effective vaccination programme to protect the uninfected while infection dies out.

REPEATING THE CYCLE OF TESTING AND DECISION MAKING SHOULD BE AN ONGOING PROCESS, WHICHEVER DECISIONS ARE TAKEN. IT MUST BE REMEMBERED THAT VIRUS MAY BECOME PRESENT WHICH HAS NOT BEEN REVEALED BY THE INITIAL TESTING PROGRAM.

A recommended approach to bulk milk

BVD surveillance on the dairy farm

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Prevaccinated homebred youngstock at 6-18 months

Annually blood antibody ELISA test 5-10 from each management group

All -ve All +ve Some +ve Some –ve

Group has been exposed to BVDv. Naive or

all PIs Possible current outbreak

Tissue or blood test one or more of the group, for antigen

Tissue or blood test all youngstock for antigen

+ve result -ve result

retest in 3 wks to check for transient infection PI Slaughter Vaccinate Pre service Vaccinate youngstock 2 3

A recommended approach to testing

dairy youngstock or beef herds

This approach to surveillance is ideally suited to beef suckler herds or to confirm if dairy youngstock have been exposed to virus. NML recommends that every surveillance structure is generated according to instruction from the veterinary consultant for the respective holding.

For more information about specific test services please go to

www.nationalmilklabs.co.uk

Or contact customer services on 08447 255 567

KEY Test selection Interpretation Test result Vaccination Vet input 1

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1. If all selected animals are negative for antibody it indicates that the animals are naive or persistently infected. It is unlikely that all animals in such a group would be persistently infected but a decision must me made as to whether further testing is necessary.

2. If current infection is likely, a decision must me made whether animals should be

vaccinated to protect against infection or whether to rely on natural immunity following infection. Age, service dates etc must be taken into consideration.

3. In a naive youngstock group (for dairy) or a naive herd (for beef), one must decide

whether to protect the herd using vaccination or tighten up biosecurity protocols.

REPEATING THE CYCLE OF TESTING AND DECISION MAKING SHOULD BE AN ONGOING PROCESS, WHICHEVER DECISIONS ARE TAKEN. IT MUST BE REMEMBERED THAT VIRUS MAY BECOME PRESENT

WHICH HAS NOT BEEN REVEALED BY THE INITIAL TESTING PROGRAM.

Further testing may include:  Bull testing

 Testing purchased animals

 Tissue testing calves to provide provenance for sales  Routine surveillance of the milking herd (for dairy)

A recommended approach to bulk milk

BVD surveillance on the dairy farm

The importance of Veterinary advice - considerations for decision making

For more information about specific test services please go to

www.nationalmilklabs.co.uk

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