Farm Ireland

Thursday 23 March 2017

Find and cull PIs in your herd to get the upper hand on BVD

Pearse Kelly

One of the first bovine diseases that Animal Health Ireland has set its sights on eradicating is BVD (Bovine Viral Diarrhoea).

If you blood test cattle on most dairy or beef farms, you will find that a lot of them will have antibodies against BVD.

This does not mean you have a problem though. All this tells you is that those cattle came in contact with the virus at some point, were probably sick for a short while, got over it and in the process developed antibodies against it.

However, the farms that do have a problem are those that have an animal that is a carrier of the disease itself and are shedding it daily in huge amounts. These are called persistently infected, or PIs.

These PI animals must be identified and got rid of. If not, they will continue to infect stock on the farm which can lead to a lowering of their immunity, allowing in many other diseases which cause hardship and severe economic loss.

Many PIs will show signs of the disease and die before they are two years of age. However, we are told that up to 30pc of PIs will never show any signs and can stay in a herd for years causing problems. So how can they be found?

The Animal Health Ireland plan to find PIs was to begin towards the end of this year. It may be delayed because of some technical difficulties but this does not mean that farmers themselves cannot start the screening process on their own farms.


It is now widely agreed across the industry that the most straightforward method to find them is through testing a small amount of tissue taken from the ear of the animal. This 'ear-notch' test can return a result within a matter of days. The screening process involves the following:

•All calves born on a farm are tested at birth (cost €5-6/hd). Ear notch is collected in a small vial at the back of an ear tag that is inserted. Calves that are negative need no further action.

•A positive result means the calf more than likely is a PI. It should be isolated and retested again two to three weeks later.

•Any calf found to be a PI has to be culled through slaughter. The sooner this is done the better for your farm's health.

•A cow that is a PI will always have a PI calf. If, then, you find a calf that is a PI you should immediately test its mother. If the cow is not a PI it means she was infected during pregnancy and this is why her calf was a PI (this is how a PI is produced -- ie, an animal can only become a PI while it is in the womb).

•All PI cows should also be slaughtered as soon as possible.

Once you are satisfied that you do not have a PI in your herd, BVD can be kept out by doing the following:-

•Follow a strict biosecurity plan to stop any new PIs from getting into the herd.

•Blood test a number of weanlings each autumn to see if there are any antibodies showing up for BVD. There should not be antibodies present if there is no PI in the herd. If there are antibodies, then a PI may have got in and needs to be identified and removed.

•Use the ear-notch test on any calf born to a purchased in-calf cow or heifer. The animal may be clear but she could be carrying a PI calf.

Indo Farming