Schmallenberg hits hard in South West

Schmallenberg has caused tremendous losses in sheep flocks across the South West, and farmers are entering the spring calving period with a mixture of hope and dread.

According to an informal survey by the NFU, 35% of sheep farmers and 40% of cattle producers in the region have suffered from Schmallenberg infection on their farm. Of those, an average of 13% of the sheep flock and 30% of the cattle herd had been affected, although that varied widely from 1% to 100%, said Matthew Uren, Dorset NFU adviser.

Common problems

Speaking at a meeting at Kingston Maurward college this week, he said the most common problems had been malformed foetuses and poor fertility in sheep, with cattle most affected by abortions. In a snapshot survey of vets, 43% of 14 veterinary practices had seen acute infection in adult dairy cows, leading to reduced milk yields, fever, poor fertility and diarrhoea.

“About 45% of practices have seen an increase in work to identify Schmallenberg and assist with lambing and calving,” said Mr Uren. “But there are still a lot of farms left to calve, so numbers are likely to increase.”

Other problems included ‘brain-dead’ calves, and even apparently healthy calves dropping dead at three to four weeks old. However, without blood tests, it was impossible to tell whether Schmallenberg was present without symptoms, or if problems were due to other infections or environmental conditions, he added.

Tim Crawshaw, veterinary inspection officer in the South West, said Schmallenberg antibodies had been discovered in cattle across most of England and Wales. “We are hoping that, as a result, quite a large proportion of animals are going to be immune.” Individual animals that had been exposed to the virus were likely to be immune to infection in the following year – but that did not mean that whole herds or flocks would have immunity, he added.

Infection period

The critical period of infection seemed to be between four and eight weeks’ gestation in sheep, and eight to 14 weeks’ gestation in cattle, said Mr Crawshaw. However, not all animals that became infected would display symptoms, as some lambs could be born healthy while their twin was deformed, for example.

“In 2012, late lambing flocks were most affected – this year it’s been early lambing flocks, as the midges were most active from June to August. In the past month there have been very few problems in sheep – but we are entering the high-risk period for spring calving herds. That said, we’ve had deformed lambs and calves nearly every month since we first diagnosed Schmallenberg. There are peaks and troughs, but midge activity is year-round whenever we have some warm weather.”

Vaccine

Paul Williams, livestock veterinary adviser at MSD Animal Health, said a vaccine against the disease had been developed. It was currently in the fast-track registration process, and although it should be available later this year, he could not confirm when it was likely to be approved.

In the meantime, there were some practical options that farmers could adopt to reduce the risk of disease. Blood tests could identify stock that had already been exposed to the disease, and were therefore likely to be immune to active infection, he said. Bulk milk tank tests could also identify Schmallenberg antibodies, although they would not show individual levels of immunity.

Farmers could delay tupping or bulling until midge activity decreased, and delay breeding from ewe lambs in a bid to establish natural immunity before they became pregnant, he added. Housing livestock, or moving them to lower risk areas, could be another option.

The use of ectoparisiticides to kill midges on livestock, dung heaps or housing, could also be of benefit, particularly when quarantining new animals brought on to a farm from a high-risk area. “However, these chemicals tend to concentrate in the wool, whereas midges love biting non-hairy areas, so I think their use is quite limited. They won’t stop the midges from biting, but may kill them before they can move on to bite again.”

Given that the disease had been identified only in 2011, information about how long animals would become immune for – or how long the vaccine would be effective – was sketchy, said Mr Williams.

To help the industry collate as much information about the disease as possible, farmers should fill in the lamb crop survey.

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