25 July 1997

MV MONITOR AIMS TO STEM A RISING THREAT

New evidence shows the number of maedi-visna infected sheep in commercial flocks is rising, prompting the launch of an MV monitoring scheme. Jonathan Riley reports

OVER 100,000 sheep in the UK are infected with maedi-visna which can cost producers up to £32 a ewe in lost performance and increased mortality.

SAC vet Barti Synge says that MV was introduced with imported pedigree sheep but has now been passed to commercial flocks.

Following the results of over 44,000 blood samples taken to establish MV prevalence in UK commercial flocks, two ewes in a thousand are now known to be infected with the virus.

"This may not appear significant but the disease is highly infectious, incurable, and has spread to flocks throughout the UK," says Mr Synge.

MV is transmitted between animals in close contact and inhalation via droplets from the nose and mouth. Lambs sucking infected milk and cross contamination of blood from punches and needles also spread the disease.

"MV develops slowly over four to six years – causing pneumonia, paralysis, wasting, arthritis and mastitis – by which time the disease will probably have spread to 60% of the flock," he explains.

"We cannot, therefore, afford to be complacent and should learn from the experience of other countries such as Iceland. We must act to prevent the disease devastating flocks while the number of MV infected sheep is still small," says Mr Synge.

Catherine Milne of the SAC advisory service says that in Iceland, where MV was first identified, 105,000 ewes have died from the disease. A further 650,000 sheep were then slaughtered in an eradication programme which took 30 years to complete.

"A recent outbreak in the UK led to 68% of the flock becoming infected, a ewe mortality rate of 14% and a third fewer lambs. Total cost in lost performance was £32 a ewe.

"Costs are incurred through depressed lamb growth rates, and deaths caused by poor milk yields and inadequate colostrum. Extra feed, vet charges and the culling of infected animals also add to costs," explains Miss Milne.

To eradicate the disease from flocks Miss Milne suggests three possible options; complete flock replacement, blood testing and culling of positive animals or removing lambs at birth and rearing them artificially.

"Complete flock replacement is often necessary because the first indication of MV infection is when symptoms develop," says Miss Milne.

"By this stage the majority of the flock will have been infected so a clean start will be a more viable option in most commercial flocks than blood testing to identify which animals are MV free.

"However, in high genetic merit flocks, blood testing and culling out infected ewes could be viable. The third strategy of removing lambs at birth – that is before they can contract MV through the ewes milk – will also be inviable in most large commercial flocks but could be an option for smaller flocks," she says.n

MV is highly infectious, incurable, and has spread to flocks throughout the UK, warns SAC vet Barti Synge. The monitoring scheme will help producers source MV-tested sheep says development officer Alison Braddock.

MV TRANSMISSION

&#8226 Close contact.

&#8226 Infected milk.

&#8226 Blood from needles and punches.