‘We have lost 300 sheep to bluetongue and the virus will come back anyway’

While the midges that transmit the bluetongue virus are still in winter dormancy, the same peace among farmers is hard to find. “All our lambs, born from ewes that survived bluetongue, remain small, no matter how well we feed them,” says Martin Reitsma, sheep farmer from Friesland. With the prospect of warmer weather, fears of a second wave are also increasing.

In the spacious, open barn, the sheep seem to nibble peacefully on their feed. Reitsma rests his eyes on a very delicate lamb. “Do you see this little one here? Eight weeks old, only five kilos”. According to him, the peers of this lamb weigh about five kilos on average.

Farmers are still dealing with the consequences of the bluetongue virus outbreak last September. This virus, transmitted by midges (a species of mosquito), is mainly fatal to sheep. Recent data from Statistics Netherlands show that the sheep population in the Netherlands decreased by 8.4 percent last year compared to 2022, which equates to a loss of 61,000 sheep. In Friesland, the province with the most sheep in the Netherlands, the decrease was even 11.5 percent.

We are working hard on a vaccine that is effective against bluetongue. Wageningen University & Research (WUR) is eager to test new vaccines and then introduce them as quickly as possible. “As soon as there are vaccine candidates, we can quickly test their effectiveness,” says WUR researcher Melle Holwerda. “If a first candidate is immediately promising, the first vaccinations could be given in the summer. However, this depends on so many factors that this is only feasible in the most optimal situation.”

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After-effect

Due to winter temperatures, the midge is now hardly active. But sheep farmers are still confronted every day with the impact of the outbreak in the previous season. Not only because of the loss, it also seems that newborn lambs are affected. This concerns lambs from ewes that were infected with the bluetongue virus.

“Our flock consisted of 2,100 sheep,” says Reitsma. “We have lost 300 sheep due to bluetongue, a loss of 2 tonnes for us. It is difficult to say how many were actually infected and survived.”

“Our lambs were already born in December,” Reitsma continues. “As a result, they will be independent by April and we can use our sheep early to graze in municipalities. We use Suffolk rams, which can mate earlier than most breeds.”

sheep farmerHarry Jansen A number of lambs were born deformed

Reitsma gestures to a dividing gate in the shed. “On the right are the healthy, fully grown lambs. The little ones on the left are descendants of sheep that we are almost certain were infected. We keep them separated to prevent the larger lambs from eating all the feed.”

He then points to a sheep with bald spots. “This sheep survived bluetongue, but still looks bad. We have had ewes that contracted bluetongue and then gave birth to their lambs prematurely and not viable. Believe me, it is truly heartbreaking.”

Reitsma fears the warmer weather. “Bluetongue will come back anyway and a new outbreak would mean the end of our company. Our only hope is that a vaccine is available in time. If that only comes in the summer, then it will be too late for us.”

More mortality among lambs

Sheep farmer Harrie Jansen from Schaapskudde de Belhamel in Warnsveld, owner of a flock of 375 sheep, was also affected by the bluetongue virus in October. “Normally, about 10 percent of our matings do not lead to fertilization in the sheep. This year that percentage has increased to 25.6 percent,” says Jansen. In addition, 25 percent of lambs born were stillborn or died within a week of birth, a large increase from 2 percent the previous year.

“A number of lambs suffer from pneumonia, heart problems or show deformities. We do everything we can to keep them alive, but we have never experienced this before. During a difficult delivery, we even had to cut off the head of a lamb to save the sheep,” says Jansen.

Royal GD, an animal health laboratory, is investigating whether the current bluetongue serotype 3 is responsible for the deformed lambs sent for testing. Although no direct link has been found so far, research from last winter shows that the virus can also infect unborn lambs, reports Royal GD. Research into a possible link with deformities continues.

According to Margit Groeneveld, veterinarian and sheep expert at Utrecht University, there is a logical explanation for the problems that livestock farmers report with lambs. “A ewe that is recovering uses so much energy for its own recovery process that less energy is left for its lamb. This can also result in reduced fertility or a malfunctioning placenta, leading to insufficient nutrition for the lambs.” Although bluetongue does not appear to be the direct cause, it can indirectly contribute to these problems through secondary effects, Groeneveld concludes.

Survivability

The survival rates of lambs appear to vary depending on the stage of pregnancy at the time of infection. Reitsma’s sheep, already pregnant for four months, were almost fully grown when they became infected – the lambs are small but survived. In contrast, in the Belhamels flock, the ewes were only pregnant for a month when they became infected; significantly more lambs have died.

According to Holwerda, it is complex to determine whether lambs are affected by the bluetongue virus. “No research has been done yet. Moreover, a large proportion of the lambs have yet to be born.”

sheep farmerHarry Jansen During a difficult birth we even had to cut off the head of a lamb to save the sheep

Groeneveld predicts a significant difference in the number of lambs that will be born in the coming lambing period compared to previous years. “As for abnormalities, a lamb weighing only 5 kilos instead of the usual 30 could be the result of a recovering ewe. I just don’t expect we’ll see this on a large scale.”

Groeneveld is convinced that the virus will return in the spring or summer. “When it comes depends on the weather, hopefully we have a few months of delay until it really starts.”

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