Bovine Viral Diarrhoea
What is BVD and why is it important?
Bovine Viral Diarrhoea is well established within British herds and is causing
thousands of pounds of production losses each year for farmers. It is estimated that
90% of farms have had some exposure to BVD. The problem with BVD is that it can
remain in your herd without causing sudden large-scale losses and therefore remain
unnoticed.
How will it affect my herd?
The virus itself doesn’t cause too much harm or damage to the animal but it is the
repercussions of the virus within the herd that causes the damage. BVD can cause abortions,
poor fertility, drop in milk and meat production and animal become more susceptible to
other diseases such as pneumonia. The main problem occurs with the production of
persistently infected calf (PI).
How are PI calves born?
If cows contract the virus when they are in early pregnancy, the foetus is often aborted or
resorbed. If cows contract the virus in later pregnancy, the foetus can be prematurely
aborted. The problem arises when cows contract the virus half way through pregnancy,
usually 100 – 200 days pregnant. In this situation, the virus enters the foetus and becomes
part of the foetus. This means that the calf, when born, will not recognise that it carries a
virus.
How are PI calves a problem?
As the calf doesn’t recognise that it carries a virus, the virus is free to replicate and sheds in
high numbers. This means that BVDv will constantly challenge animals in contact with the PI
calf and that more animals will contract the virus becoming more susceptible to other
diseases, high rates of abortion, poor fertility and the creation of more PI calves. A normally
born calf cannot become a PI calf and a PI calf cannot be cured of BVD, unfortunately the
animal will succumb to a disease called mucosal disease. The animal will develop diarrhoea
with mucus present and develop pneumonia, which can’t be treated. There is no treatment
for this or any way of curing a PI calf and the animal will die.
How do I know if I have got a PI calf?
As stated before, the calf doesn’t recognise that it contains the virus so PI calves can and do
grow normally. This makes the disease very hard to spot early on and often damage has
been done before signs are seen. Sometimes PI calves can appear stunted in growth or
appear to be unwell for long periods of time but other times the calf can appear perfectly
healthy until it develops mucosal disease.
What should I look out for?
If you are experiencing any of the for mentioned problems such as poor fertility, abortion or
high numbers of pneumonia, it is worth checking for BVD. Remember, it may not show as a
sudden large loss but more of a low grumbling problem.
How do we check for BVD?
First off, contact ourselves if you have any concerns regarding BVD, there are a number of
ways to help and each can be tailored for individual farms. There are three ways to test for
BVD, blood sampling, milk sampling or ear tag testing. If you suspect that you have a PI calf,
blood testing is the quickest way to find out. Ear tag testing, which cost a small amount
more than regular ear tags, can identify problem animals from a young age and can prevent
long term problems becoming established. Bulk milk testing can help identify a problem in
the herd with minimal intervention.
How do I get rid of BVD from my herd?
Once again, it will be tailored to individual herds but the most important factors are finding
and removing PI calves from the herd and vaccinating all breeding animals for BVD. Hunting
for PI calves can be costly but the savings can reach into the thousands. All breeding cattle
should be vaccinated with a double dose prior to the bull entering to ensure that the cow is
protected when pregnant. Six month to yearly boosters are then followed up to ensure BVD
doesn’t get back into your herd.
If you have any concerns or worried that BVD may be a problem in your herd, please don’t
hesitate to contact us.