What is BVDv?

BVDv is Bovine Viral Diarrhoea virus, a virus that can infect cattle.

What does the virus do?

As the name suggests the virus can cause diarrhoea in cattle. It is very often associated with fertility problems in cows and heifers, and also has a detrimental effect on the immune system of animals.

What is a PI animal?

A PI animal is an animal that is Persistently Infected with BVD virus.

There are two types of BVD infection

1. Acute infection: an animal that has not been in contact with the virus before is exposed to the virus in the environment*

This animal carries the virus for 2-3 weeks and young animals can get quite sick during this period, with scours and pneumonia. The sickness associated with acute infection in young animals is usually due to the immune system of the animal being suppressed by the virus. In breeding animals acute infection is associated with infertility, early embryonic death, abortion etc.

Breeding animals exposed to BVD virus:

• Pre breeding-day 40: poor conception rates, early embryonic death
• Day 40-120: birth of PI calves
• Abortion at any stage of gestation
• Weak calves

2. Persistent infection- a PI animal

PI animals are produced when an in-calf cow or heifer is acutely infected with the virus (as 1 above) from day 40 to 120 of pregnancy. The virus can cross the placenta and infect the foetus. The foetus is not able to clear the virus the way its mother can because its immune system is not developed properly at these early stages of life. PI animals are born carrying the virus and will shed large amounts of virus into the environment. PI animals can die quite young but some may reach breeding age. Many PI animals look like screw animals and some develop mucosal disease.

What is Mucosal Disease?

Mucosal disease is a complex disease that only affects animals that are Persistently Infected with BVD virus. BVD PI animals that become infected with another strain of the virus can develop mucosal disease with clinical signs of progressive diarrhoea and mouth and feet lesions.
Animals with mucosal disease usually die within a few weeks of developing the disease.

How do I test for BVD?

Blood and milk can be tested for both virus and antibody. BVD antibody positive means the animal(s) have been exposed to the virus in the past. BVD antigen (virus) positive means active infection in the herd, and/or presence of a persistently infected animal(s). PI animals should be identified and removed from herd.

Why should I vaccinate for BVD?

There are two types of vaccination for BVD:

1. Vaccinate cows to prevent birth of persistently infected calves
2. Vaccinate young stock to prevent immunosuppressive effects of BVD which can precipitate scours and pneumonias.

Vaccination of cows should take pre-breeding so that maximum immunity is in place before the crucial day 40-120 of pregnancy, when PI calves can be produced.
If using a 6 month vaccine ensure you divide the herd into batches for vaccination so that all cows and calves are covered for the first few months of the pregnancy at least. If using a 12 month vaccine you can vaccinate the entire herd at any stage of the year. When starting a BVD vaccination programme for a breeding herd ensure you have the programme complete pre breeding so maximum value is got form vaccination.

Vaccination of young stock to prevent immunopsuppression due to BVD should take place prior to time of mixing, stress, housing etc. Rispoval 3 RSV, Pi3 BVD provides cover to young stock against BVD as well as virus pneumonia.

How common is BVD?

It is estimated that over 90% of Irish herds have been exposed to BVD.

*environment:

The BVD virus may survive for up to a month in the environment. It can come onto a farm on shared machinery, vehicles etc. The highest risk of bringing in BVD to a herd is by purchasing infected or carrier animals. Biosecurity is every bit as important as vaccination to control BVD infection in your herd. Make sure you know where you are buying animals from and the disease status of the herd.