BVD – Bovine Viral Diarrhoea: Is it limiting your profit?

BVD – Bovine Viral Diarrhoea:  Is it limiting your profit?
BVD is widespread throughout New Zealand and, in its most severe form in young stock, is seen as Mucosal Disease. It is a complex disease and presents in different ways depending on a number of factors including the level of infection in the herd, the timing of introduction of new infections, the number of carriers in the herd and level of herd biosecurity.

Financial losses due to BVD can be significant in individual herds though not always obvious; it has recently been estimated that, in an infected herd, losses can be between $3,000 and $9,000 per 100 cows.

Although infection with the BVD virus can cause diarrhoea in calves and yearlings, a large proportion of the losses do not involve diarrhoea, despite the name. The disease can present as abortions, stillbirths, a low calving percentage, calves that are ‘poor doers’ and/or respiratory disease.

Although a proportion of carrier animals (or Persistently Infected or PI animals) will be sickly, some are born normal but become ill and often die later in life, usually before 2 years of age. However, some will appear ‘normal’ for their entire life and PI’s up to 8 years of age with no obvious signs have been recorded. For this reason, breeding bulls can be a PI and if the cows have a low level of immunity, are unvaccinated or have never been exposed to BVD virus before (typically heifers) the introduction of new infection can cause a dramatic reduction in calving percentage. This will result in potentially high numbers of PI’s born in a single season. However, in most herds BVD exists at a low level with only a few new cows infected each season resulting in a less obvious reduction in productivity.

Animals become PI’s in utero and will remain that way for life. If they reach breeding age, they will give birth to a PI calf every year. This means that testing for a PI is a ‘test for life’ with these animals identifiable by blood test or ear notching.
Most dairy farmers who buy breeding bulls, including beef bulls for tailing off the herd, require them to be tested for their PI status and then vaccinated for BVD.

Vaccination will have no effect on a PI animal, which means that any PI cow left in the herd will continue to produce PI calves even after vaccination. However, vaccination of the rest of the herd protects any naïve animals and their unborn calves from catching the virus from the PI animal.
Weaning and pregnancy testing are good times to assess the BVD situation on your farm. If you find at weaning that you have fewer calves than expected due to higher than predicted calf deaths or that some calves stand out as being relatively poor for no obvious reason, BVD could well be involved. Remember BVD may have been in the herd for several years, with calving percentages falling slowly, so be critical with your figures and look back a few years to see if the situation has gradually changed.

Every farm needs a different control program depending on the individual situation and this should be discussed with your vet. Some types of operation may need to do nothing, while others may need to improve biosecurity and quarantine measures. However, most herds will require some testing for the BVD virus to identify the level of infection. This can be done initially on pooled samples to reduce cost. Depending on the level of infection found further investigation to identify PI animals and/or continued monitoring or vaccination may be recommended.
If you are selling bulls to other dairy farmers for breeding, the bulls should be tested and given two vaccinations for BVD 3 to 4 weeks apart. To be most effective this should be completed at least one month before the bulls are due to leave your farm.
When buying bulls for your breeding herd you should check their BVD status and make sure they are vaccinated. Breeding bulls should also have an annual booster vaccination.

Talk to your vet about completing a risk assessment for BVD on your farm. The type of farming operation you have will determine the best plan to minimize the financial impact of BVD.

Date Added: Wednesday, 23rd December 2015