7 August 1998

BVD VACCINATION BRINGS WELCOME SPIN-OFF BOON

Dairy producers could be

losing money through BVD in

their herd. Jessica Buss

looks at the cost of control

VACCINATING against bovine viral diarrhoea virus could be worth £35 a cow in improved fertility alone.

That is the finding of a study by vaccine manufacturers C-Vet on 10 dairy herds with a total of 497 cows. Half the cows in each herd were vaccinated with Bovidec before service, after matching pairs of cows for lactation number. The other of each pair was left unvaccinated, says C-Vet vet adviser, Andrew Curwen.

Vaccinated animals had shorter calving intervals, needed less semen and fewer were culled, he adds. Conception rate to first service was 68% for vaccinated cows and 51% for unvaccinated cows. Unvaccinated cows, therefore, needed 1.8 service a cow compared with 1.5 for vaccinated cows. At a cost of £20/straw that difference was worth £6/cow.

The vaccinated cows also took 3.4 fewer days to conceive, saving £5.75 on calving interval. Current DAISY estimates each day a calving interval is extended to be worth £1.69/cow.

But the greatest benefit of vaccination was a reduced culling rate – 5% compared with 9% for unvaccinated animals. The difference of 4% in culling rate was worth £23.12 using DAISY estimates of each cull costing £578.

"This does not represent the full costs of BVD which include abortion, mucosal disease and making other diseases worse," stresses Mr Curwen. He points out that management, nutrition and genetics also affected herd fertility results.

Another C-Vet survey, which tested bulk milk samples from 1000 dairy herds, showed only 3% of herds free of BVD antibodies.

The bulk milk test gives an indication of the number of cows that are producing antibodies whose milk going in the bulk tank. In 69% of herds C-Vet estimates antibodies are present in over 65% of cows, 18% of herds have 25-65% of cows producing antibodies, and 10% of units have 5-25% antibody positive, says Mr Curwen.

To indicate BVD status, he advises bulk milk testing and blood sampling a selection of heifers between eight and 18 months old.

When BVD is present and producers decide to vaccinate, the vaccine must be given to animals at least four weeks before service, and after calving. Two doses must be injected, subcutaneously, three weeks apart, and this must be repeated after each pregnancy.

There may also be scope for strategic use in some herds, in consultation with your vet, he says. For the cost of vaccine contact your vet.

Mr Curwen admits that eradication programmes can eliminate BVD from dairy herds. But he warns eradication produces a herd which is susceptible to BVD, and because BVD is widespread it is can easily be brought onto the farm.

BVDCOSTS

&#8226 Higher culling rate.

&#8226 More services/cow.

&#8226 Longer calving interval.

Conception rates are higher in cows vaccinated against BVD, according to Andrew Curwen. But the main benefits come from reduced culling rates.