BVD could be “baa-d” news for sheep-and-beef farmers
Bovine viral diarrhoea (BVD) virus has been causing major economic losses for New Zealand beef farmers for more than 50 years and the effects could be even greater when you account for the potential spillover of BVD into sheep flocks that are co-grazed with BVD positive herds.
Background
Similar to cattle, pregnant sheep that become transiently infected with BVD can have problems with fertility, abortions, stillbirths, and lambs that are born with birth defects or persistent infections. This is a particular concern in New Zealand since an estimated 45 to 55% of beef herds are infected with BVD and it’s relatively common for farmers to graze their sheep flocks in the same pastures as cattle. Previous research from the 1970s showed that about 30% of sheep sampled at slaughterhouses had antibodies against BVD and the latest research from the BVD Free New Zealand project highlights that the problem still remains.
Methods
In the 2018 study, eighteen sheep flocks from across New Zealand were recruited through the VetLife and VetEnt clinics. This included 9 flocks that had been co-grazed with known BVD infected cattle and 9 flocks that had been co-grazed with known BVD negative herds. Blood samples were collected from 15 two-tooth ewes in each flock and submitted for both pooled and individual antibody testing using the p80 ELISA at Gribbles Veterinary Pathology, which measures the level of antibodies in the blood.
Results
The results showed that two of the 9 flocks co-grazed with BVD infected herds tested positive for antibodies while none of the flocks that were co-grazed with known negative herds had evidence of previous exposure to the virus. The results are a little tricky to interpret because the p80 ELISA cannot distinguish between antibodies produced against BVD from those produced against the closely related Border Disease Virus (Hairy Shaker Disease), but further testing of the samples with a Virus Neutralisation Test (VNT) suggested the antibodies were most likely against BVD. There was also no available data on flock performance to see if there was impact on reproduction and lamb growth in the affected flocks, but it certainly something to consider as a potential cause for sheep flocks that are not performing at expected levels.
Clinical Relevance
One of the main concerns raised about these findings is whether the presence of BVD in sheep flocks could make it more difficult to eradicate BVD from cattle populations. Although we know that it is possible for persistently infected (PI) lambs to transmit BVD to cattle under experimental conditions, the virus is not well-adapted to sheep and so it tends to die out quite quickly in affected flocks. This means that controlling the disease in cattle herds should be effective for controlling the disease in sheep flocks and could be bringer even bigger benefits to industry by eradicating BVD from New Zealand.