Eradicate BVD with Help from your Veterinarian

By Sarah Ravenscroft, Gribbles Veterinary Pathology. March 2006.

We have highlighted some of the key risks associated with BVD virus with particular relevance to heifer rearing operations. With this in mind, we will look at the ways in which we can assess our herd (and bull) status to keep our heifers and their future offspring free of disease.

As pointed out in the last bulletin, the key areas where BVD can gain entry into our herd are:

1. through introduced bulls used for natural mating
2. through PI (persistently infected) animals already circulating within the herd.

The introduction of the bulls to the potentially naïve herd is an especially important area to consider. Any PI bull entering the herd at this time can infect not only the heifers he services, but also the animals previously submitted for AB. This can result in early foetal loss, abortion or the development of more PI calves!

Range of BVD Tests

Depending on the status of the herd, different tests are used to check for BVD. Testing for BVD is essential for not only diagnosing and removing infected animals, but also for forming preventative strategies to continue to protect your herd. Your vet will help decide on the most suitable testing options.

As a guide, the following tests are used:

• For service bulls, a particular blood test can pick up the PI animals (BVD antigen ELISA). Any animals positive for this antigen is likely to be a PI animal. If a positive bull is particularly valuable, you could re-test it after a few weeks to be sure. A previous vaccination will not interfere with the result, and the test should be considered critical to maintaining biosecurity in your heifer mob. This test can also be used to isolate BVD in aborted foetuses.
• Heifers can also be blood tested, but the type of test will depend on whether you want to know if the mob has already been exposed, and/or whether you are looking for a PI heifer in the mob. Most surveillance and/or eradication programmes include combinations of both types of test.
• An ear notch skin test is available for calves less than 3 months old. Farmers rearing bulls from the dairy industry may want to screen the calves at a young age so they don’t have the costs of rearing a PI calf. This test involves taking a small notch of skin from the ear (eg using sheep or pig ear markers).
• A test can be done on a sample of milk from the vat to assess the level of exposure within the herd. It will not be able to identify individual infected animals but the result will imply whether the herd is likely to contain infected animals or not.

Shortly a new test (PCR) will be available, which will allow us to screen large numbers of animals for a positive PI. This will mean significant cost savings for farmers wanting to identify a small number of PI animals within a herd, by using pooled samples.

More Awareness Needed

Currently there is a BVD eradication steering committee formulating Standard Operating Procedures for control and eradication of BVD within New Zealand.

The steps for eradication of BVD on individual farms depends on the level of infection, and the potential risks in each situation.

Control strategies can therefore only be formulated after diagnosing and assessing the level of infection on each individual property.

It is essential that any control strategy is worked through thoroughly with your veterinarian.