Herds using tissue tags can achieve negative status once ALL calves born in a 12 month period have been tested for BVD virus with negative results. Many herds have been tissue testing for over 12 months and a quick glance at their testing history suggests that they should be eligible for negative status. Unfortunately when we check the data in ScotEID we are discovering gaps in testing. Now is a good time to review your BVD status. This will allow time to plan to carry out any necessary blood sampling when animals are next handled/housed.
The problems we are seeing include:
- Calves have been tissue tagged but the sample was unsuitable for testing. In most cases this means that no tissue was present in the sample tube. Tissue degeneration has been a problem in a smaller number of cases.
- Small numbers of calves have been missed – often only 2 or 3 over the course of a few months.
- Calves have been tested but have an inconclusive result in ScotEID. This is uncommon.
- A full year of calves has been tested for BVD virus with negative results but we are unable to give negative status. This can be due to the continued presence of an older PI animal on the holding or because less than 12 months have elapsed since the removal of a PI. Negative status can only be given once all calves born in the 12 month period after the removal of all PIs have tested negative.
For farmers that want a negative status what can be done?
Calves without a negative BVD virus result in ScotEID, and still present on the holding, should be tested. Things are more complicated if these calves have died or been sold. If a calf has died or has been sold (and not subsequently tested) we cannot prove that they were not PIs. There are three options:
- Continue to tissue tag test all calves born. The start of the 12 month testing period will be the day after the untested calves died or were sold off the farm.
- ScotEID also lists the status of all cattle currently on a holding. If most calves have been tissue tested for a year or more, then most cows will have an assumed negative status. For some herds only a handful of animals would need to be tested to complete a whole herd screen and allow negative status to be given.
- For herds where no PIs have been present on farm during the previous 12 months carry out check tests on suitable groups of young stock. Say if they have been BVD vaccinated, when this was carried out and which vaccine was used. This option is not appropriate if Bovela has been used.
Once a negative status has been achieved on the basis of a 12 month calf tissue tag screen this is valid for 13 months unless a PI is detected. The sensible option is to continue to tissue tag. It is your responsibility to ensure that all calves are tested so that their negative status is not invalidated 12 months down the line.
Heather Stevenson, firstname.lastname@example.org.
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