Mandatory bovine viral diarrhoea screening: guidance for vets

PART 6 HERD STATUS DECLARED - WHAT NEXT?

The laboratory will inform the keeper of the herd status, and you may want to be able to advise your clients of what they should do next. This section gives you some guidance on what should be done whether the status is negative or not-negative.

You should always advise clients to send PI cattle straight to slaughter

Herd which has a negative herd status for BVD

A negative status is something your client should try to protect.

Though a negative herd status is good news for your client, on its own it is not as good a standard as a CHeCS-approved BVD-free status. It is also only a snapshot - risks of disease incursion remain and need to be considered.

You may wish to discuss biosecurity with your client. This is a good time to create or review a biosecurity plan, vaccination programme and a schedule for future surveillance sampling. You could also agree the actions to take should any incident of disease or breeding failure occur that could be attributable to BVD infection.

Herd which has a not-negative herd status

From December 2012 it is likely that there will be consequences to having a not-negative status. There will be a detailed consultation on these in Spring 2012, but at the time of publication these are intended to be:

• A ban on knowingly selling a PI animal.
• A declaration of herd or animal status when selling or moving cattle.
• Subject to consideration of timing, cattle from not-negative herds will only be able to move through a market or to another holding if tested negative for virus beforehand. Otherwise, they can only move direct to slaughter. This may be regionalised and delayed.

Keepers with not-negative herds may seek your advice on how they can become negative. To become negative they will have to take steps to discover if they have any PI cattle and, if so, remove them. To do this they will have to carry out more testing.

There are several different ways to conduct follow-up testing. You may find the following advice helpful in deciding on a follow-up testing strategy.

Conducting Follow-Up Testing

Controlling BVD entails identifying and removing PI cattle and ensuring no more are born on or brought to the farm. Any control programme requires considerable thought and a substantial commitment. It should be clearly defined, realistic, constantly reviewed and sustainable. The vet CPD module includes flow diagrams for BVD eradication. Possible control and eradication procedures can be summarised as follows:-

Beef Herd

• All bulls and immature cattle ie. in-calf heifers, youngstock and calves (usually older than one month) and any cow that is not the mother of an animal being tested are individually blood tested for BVD virus. Continue blood testing for virus all calves born into the herd for 12 months following the removal of the last PI animal.
• After the calf crop has been screened individually, dams of calves which are not PI do not need to be tested. Ensure breeding females which have not had a calf tested or have given birth to a PI calf are individually tested for BVD virus.
• Again, calves can be tested for BVD virus when they are ear-tagged shortly after birth using tags that collect a tissue sample. This method has the advantage that PI calves can be identified and removed before the start of the breeding season.

Dairy Herd

• The milking herd can be screened for the presence of a PI animal by testing a bulk milk sample from up to 300 cows for BVD virus by RT- PCR. If the herd is too big or if a bulk milk sample tests positive smaller pools and then individual milk or blood samples will have to be tested to identify the virus positive animal(s). Remember that in individual milk sampling, there is always a risk of cross-contamination which should be considered when analysing results.
• All other animals i.e. dry cows, bulls, in-calf heifers, youngstock and calves (usually from one month of age) are individually blood tested for BVD virus. Continue blood testing for virus all calves born into the herd for 12 months following the removal of the last PI animal.

Alternatively, calves can be tested for BVD virus when they are ear-tagged shortly after birth using tags that collect a tissue sample. This method has the advantage that PI calves can be identified and removed before spreading infection.