Risk of Schmallenberg in Lambing Flocks and Calving Herds this Spring

Schmallenberg virus (SBV) is transmitted by the biting insects of the Culicoides family (midge) and can cross the placenta to infect foetuses. Foetal deformities can occur if an animal is infected between day 28-40 of pregnancy (sheep) and 3-6 months of pregnancy (cattle). Affected lambs and calves may be born with fused joints, twisted necks or spines, shortened lower jaws and domed skulls. These malformations may lead to lambing or calving difficulties and stillbirth. Some lambs or calves may be born alive but are weak, unable to suckle, and have abnormal neurological signs. Early infection before the above critical stages in pregnancy can result in early embryonic death, seen as a high barren rate at scanning, or abortion. Infection outside these risk periods and in non-pregnant animals can result in a relatively mild illness of fever, milk drop, diarrhoea, and loss of appetite lasting only a few days. After infection, sheep and cattle have a good immune response with antibodies thought to last years. Blood sampling can be used to assess for exposure, but it is important to remember that exposure will not always lead to deformed offspring - the timing of exposure in relation of pregnancy is key.

So far this year SBV has been confirmed by SRUC vet services in early lambing flocks in Dumfries & Galloway, Ayrshire, and Stirlingshire. This suggests these sheep were infected in July – September 2024. However, mild weather into November 2024 could have allowed midges to continue biting sheep late into the season and potentially impacting March lambing flocks and spring calving herds. Although, nothing can be done now to prevent issues caused by SBV during pregnancy.

Any herd or flock reporting poor scanning results, abortions, or the birth of malformed lambs or calves should contact their vet to arrange investigation, and a vet should be called to assist in any difficult births to safeguard the welfare (and value) or the dam and offspring. SBV is only one of the many causes of these problems. Similar presentations may be seen with bluetongue virus (BTV), a notifiable disease, which has been detected across England and Wales in 2024/25, but to date no cases have been found in Scotland. Other causes may include infectious diseases, toxic insults, nutritional deficiencies, or genetic abnormalities. Therefore it is important to investigate fully to determine the cause and help the industry understand the extent of the issue this spring.

Megan Fergusson, SRUC Veterinary Services

Laura Henderson, SAC Consulting