Tips to cut Schmallenberg virus risk this breeding season

Livestock producers should consider changing their breeding programme to help mitigate the risk of contracting the Schmallenberg virus, scientists have advised.

They said the disease had survived the winter and there was now a “real risk” of it spreading further north and across the border into Wales this coming breeding season.

“We have evidence that the virus is starting to circulate again now. I see no real barriers to it spreading quite quickly to a significant chunk of the country,” Peter Mertens, disease expert at Surrey’s Institute for Animal Health, told producers at the NFU’s disease conference last week.

Prof Mertens said a vaccine had been developed, but the licensing process could take a number of months so predicted it was unlikely to be available until December.

But he said farmers could reduce the damage from the midge-borne virus.

One of the measures farmers could take is to postpone tupping until after late autumn when temperatures drop, he said.

“If the risk period of pregnancy occurs outside the midge season there is a reduced chance of problems.

“To transmit the virus, midges need two weeks to become infected and lay eggs. If you get high levels of frost it kills the midges and re-starts the cycle,” he explained.

The biggest risk period for foetal deformities in sheep is the first 25-60 days of pregnancy, while cattle have a longer and later risk period of between 62-173 days, due to the increased gestation length.

He admitted it was difficult for farmers to forecast the best breeding period, as weather conditions had become more unpredictable.

Prof Mertens said higher levels of malformation could be a result of grouped pregnancies and advised farmers to stagger pregnancy over a wider period to help spread the risk.

During the last outbreak, less than 1% of farms were infected, with many only suffering from a low number of cases, he explained.

“There were one or two farms where it was higher than this, but this was due to synchronised pregnancies, where the whole farm was pregnant at the same time.

“The biggest risk period for foetal deformities in sheep is the first 25-60 days of pregnancy, while cattle have a longer and later risk period of between 62-173 days, due to the increased gestation length.”
Professor Peter Mertens, Institute for Animal Health

“If all animals are pregnant at the same time it will run through everything and cause a significant amount of birth defects. But if the pregnancies are out of synch some will be infected outside the risk period.”

Prof Mertens said it was difficult to predict spread this time around, but weather would have a major effect on the spread of the disease in forthcoming months.

“The weather is very important. It governs first of all when the midges arrive, how many we have got and how rapidly the virus grows in the insects and how it is spread.”

He said the geographical spread of the disease meant many farms would only be marginally protected.

Previously infected animals will have now built up antibodies against a second attack and the foetus will also be protected, but animals born after an outbreak could lose protection and become susceptible later on in the year, he said.

Long term, he said there was a “good chance” the disease would burn itself out.

“The UK is quite small, so I think we will get into a position – providing the transmission rate is good – where it will run out of things to infect.”

But Prof Mertens said producers could see the virus return at a later stage if this does happen.

“In the UK the turnover of livestock is quite quick at about five years. So once we have reached 100% immunity we are going to be back at square one and the risk starts all over again.”

However, it is hoped a vaccine will be available by next year to help combat the problem.

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