2 December 2008

3 minute read

Europe

The case for all cattle farmers to pursue a determined eradication plan against BVD (Bovine Viral Diarrhea) has gained momentum because cattle Persistently Infected with BVD, so called PIs, may not respond to Bluetongue vaccination as a result of their immune-response system being damaged by BVD infection pre-birth years before. They therefore could remain carriers of the midge-born Bluetongue virus, as well as continuing to shed BVD virus every day of their lives. Such PIs, even though vaccinated, could infect vulnerable calves before they are old enough to be given Bluetongue vaccine.

However a relatively new BVD test, based on reverse transcriptase polymerase chain reaction (PCR) technology, allows owners to identify and remove BVD PIs relatively cheaply and easily – which can not only eliminate the impact of BVD within the herd but purges the carriers of Bluetongue.

“Over 85% of all UK beef herds have BVD infection and most farms will perpetuate this because about 1% of their cattle will be PIs,” explained NBA Chairman, Christopher Thomas-Everard.

“Over the years vets have advised many farms to regard BVD as an unavoidable result of keeping cattle and treat it as self-vaccinating with empty heifers being introduced to the herd in the expectation that they would be lightly infected before becoming in-calf.”

This form of protection comes through contact with a BVD PI and these make up between 0.5 per cent to 1.5 per cent of adult cattle in each infected herd.

A typical PI usually becomes infected between the 45th and 125th day of its dam’s gestation and, although many die as calves because they are vulnerable to a range of infections, some survive to become replacement heifers, or breeding bulls, and invariably continue to spread BVD to other cattle in the herd.

“Because of the high level of infection, and previously a high cost of testing, little was done about these animals. Now, however, PIs can be diagnosed, and removed, easily and cheaply as a result of tests based on PCR technology,” said Mr Thomas-Everard.

“The testing and removal of BVD PIs is a single capital investment in a herd and should be a once-in-a-herd-lifetime event. In the first year, all suckling calves, cows, replacement heifers and bulls should be tested and if any calf tests positive, its dam should be re-tested too.”

“As long as reasonable care is taken, only purchased animals need to be screened for PI from then on. The tests cost £20 for groups of 10. Each herd’s economic performance should improve markedly, resulting in savings of about £45 per suckler cow per year from reduced calf losses and fewer drugs, and up to £30 a head for store cattle after weaning, if BVD is no longer present.”

“However, until the whole country becomes clear, it is hazardous to have an unprotected (naïve) herd because one incoming stray PI could rekindle herd infection. Annual vaccination of breeding stock is recommended at about £2 / head.

Orkney, with the densest population of beef cows in Europe has shown what can be done. With 28,000 cows on 100,000 hectares, 537 Orkney farmers have cooperated together to identify and remove 402 PIs and, after further testing, their herds are proven clear of BVD. This task was started after they found post-mortem examinations of abortions and neonatal deaths showed 45 per cent were caused by BVD.”

“Now Orkney herds are rearing 1,500-2,000 additional cattle a year, generating more income as result of having fewer barren cows, fewer abortions and better thriving animals – and, should it ever become a problem to them, have also increased their potential protection against Bluetongue,” Mr Thomas-Everard added.