There is a lower risk of Schmallenberg outbreaks in early lambing sheep flocks next spring, according to Newtownards-based vet Cormac White.

Last spring, early lambing flocks across NI experienced a sharp rise in abortions and malformations due to the virus.

However, White said that widespread outbreaks of Schmallenberg last season should mean that immunity to the viral disease has developed in flocks.

“If you had exposure to it last year, the chances are you should not have cases next spring,” he said.

Schmallenberg is spread by midges and the most susceptible period for pregnant ewes to become infected and have deformed lambs is around 25 to 50 days in-lamb.

It tends to mainly impact early lambing pedigree flocks, as the key susceptibility stage of pregnancy aligns with peak midge activity in the late summer and early autumn.

However, White explained that immunity to Schmallenberg builds when ewes are exposed to the virus at any stage, so it is not just ewes that had deformed lambs last year that will have immunity.

“Even if you had just one or two cases in the spring, the rest of the flock should have been exposed at some point too, so there should be a good level of immunity,” he said.

Established

White said that the virus is likely to be well established in midges across NI, so even flocks that had no Schmallenberg cases at lambing last year could have immunity now.

“The weather that we are now having of mild winters and muggy summers is perfect for midge survival and the virus is probably endemic in the population,” he said.

Schmallenberg was first diagnosed in NI in 2012, and widespread outbreaks occurred in NI during 2017 and 2018.

White said that the pattern of previous outbreaks in NI and elsewhere suggests a flock only becomes susceptible for a major outbreak again when the ewes that had exposure in the past have been replaced.

It means a significant level of immunity should remain in flocks for several years and it is a key reason why vaccines were not manufactured by drug companies amid the most recent outbreak.

Schmallenberg can also affect cattle, and the key stage of pregnancy for picking up infections for cows to have deformed calves is between two to six months in-calf.

“Given that cases have been reported across NI, we would like to think that most cows have been well exposed and have a level of immunity,” White said.