Farm News
Dealing with Bovine Viral Diarrhoea
Bovine Viral Diarrhoea( BVD) is a disease that we as farm vets are having to deal with increasingly regularly, from running diagnostic tests to investigating and controlling infection.
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DESPITE THE NAME, BVD DOES NOT only cause diarrhoea, but can also cause a whole host of problems. These include subfertility, abortions and any disease associated with an impaired immune system, such as pneumonia and scour. All cattle systems can be affected, from suckler herds, to dairies, calf rearers and fattener / finisher herds.
The signs of BVD can range in severity from very subtle signs to acute illness and death. Often the effects of BVD are only noticeable after the disease has been eradicated from the herd. Presence of infection causes subfertility, low birth weight and slow weight gain, longer calving intervals and a higher prevalence of infections such as metritis in cows, and pneumonia and scours in calves.
BVD is a clever disease and can take different routes depending on the stage of pregnancy that an animal is infected. If a cow is exposed to BVD during early pregnancy then she may abort. Alternatively, that calf may continue to develop and will be Persistently Infected( PI) when born. PI’ s shed virus continuously and pose a huge risk of infection to surrounding animals. Cows infected will produce PI’ s or abort, whereas surrounding calves may show signs of a lowered immunity and therefore be more susceptible to infections. PI’ s themselves can be ill thriven and fail to grow. However, they can also be completely normal and therefore visual identification is impossible. An animal infected with BVD after birth cannot become a PI; an animal is born a PI.
‘ multiple vaccines are available on the market’
There are multiple ways to diagnose BVD in a herd. The most common route is to take a blood sample from a selection of young stock aged 9-18 months of age to screen for exposure to the virus. If no antibodies are found then the blood is tested for the virus itself, as PI animals will have low or no antibodies to BVD as their immune system does not recognise it as a threat. Should this second test be negative then a vaccination strategy is recommended. If any of these results are positive, further tests are carried out to identify PIs in the herd. Identified PIs need to be culled in order for eradication of BVD in a herd. PIs are identified through
blood or tissue testing. Blood testing is the quickest route to eradicating BVD in the herd but can be costly. The tag and test system takes the form of an ear tag applied at birth which takes a tissue sample; any BVD positive results from this can be taken as a PI and should be culled.
With regards to prevention, multiple vaccines are available on the market. Biosecurity is also essential and incoming animals should be screened on arrival before entering the main herd.
Contact your vet to discuss BVD in your herd.
For further information on Westpoint, please contact our York practice on 01904 486712, or visit www. westpointfarmvets. co. uk. Ashley Marshall BVetMed MRCVS Westpoint Farm Vets
24 Jun / Jul 2016 www. farmers-mart. co. uk