Arthrogryposis in Sheep: Congenital Joint Contractures in Lambs

Arthrogryposis means persistent joint contracture present at birth. In lambs, that usually looks like one or more legs held in a fixed, bent, or rigid position. The joints may not fully extend, and the muscles around them can be underdeveloped because the fetus did not move normally in the uterus.

This is not one single disease. Instead, it is a physical birth defect pattern that can happen for several reasons. In sheep, arthrogryposis is often linked to problems that affect the fetus during pregnancy, especially infections that damage the developing nervous system or muscles. Merck notes that arthrogryposis is a congenital joint contracture, and Cornell highlights it as a classic fetal deformity with some viral infections of sheep.

Some lambs have only mild limb stiffness and can nurse and move with help. Others have severe deformities, spinal curvature, brain abnormalities, or are stillborn. Because the outlook varies so much, your vet's exam is important for deciding whether supportive care, monitoring, or humane euthanasia is the kindest option.

The common thread is reduced fetal movement during development. When a fetus cannot move normally, joints may become fixed and surrounding soft tissues tighten. That reduced movement can happen because of damage to the brain, spinal cord, peripheral nerves, or muscles, or because of inherited developmental problems.

In sheep, one important cause in the United States is Cache Valley virus, a mosquito-borne virus that can infect pregnant ewes and cause abortions, stillbirths, and congenital defects including arthrogryposis, scoliosis, and hydrocephalus. Cornell reports that timing matters: infection early in gestation may cause abortion, while infection during a later vulnerable window can lead to musculoskeletal and central nervous system malformations.

Other infectious causes can also be involved depending on region. Border disease virus is a well-recognized congenital infection of lambs and can cause weak, poorly formed offspring, although tremors and abnormal fleece are more classic findings than joint contractures. Merck also notes that some viral diseases in sheep and goats can produce congenital CNS malformations with arthrogryposis. Inherited defects are possible in some lines, and Merck describes environmental teratogens, including certain toxic plants such as poison hemlock, as causes of contracture defects in multiple livestock species.

Because the cause affects future breeding and flock management, it is worth investigating. A single malformed lamb may reflect an isolated developmental problem, but a cluster of abortions, stillbirths, or deformed lambs raises concern for infectious exposure during pregnancy.

Diagnosis starts with a hands-on newborn exam. Your vet will look at which joints are affected, whether the deformity is mild or severe, and whether the lamb can stand, suckle, and breathe normally. They will also check for other congenital defects, including spinal curvature, skull changes, neurologic problems, or signs that the lamb was premature or growth-restricted.

History matters a lot. Your vet may ask about breeding dates, vaccination and biosecurity practices, mosquito exposure, toxic plant access, and whether other ewes had abortions, stillbirths, or malformed lambs. If more than one fetus or lamb is affected, that pattern can point toward an infectious or flock-level problem rather than a one-off defect.

Testing may include radiographs to define bone and joint position, but flock diagnosis often depends more on laboratory work and pathology. Cornell notes that diagnosis of Cache Valley virus can rely on fetal antibody testing because the virus may be cleared before abortion or birth. In practice, your vet may recommend submitting a stillborn lamb or aborted fetus for necropsy, along with placenta if available, plus pre-colostral samples from a live newborn. Those results can help guide breeding decisions and prevention planning for the next season.

Prevention focuses on protecting the fetus during pregnancy and reducing repeat cases in the flock. Work with your vet on breeding records, lambing surveillance, and a plan for investigating abortions or malformed lambs quickly. If one affected lamb appears in isolation, the risk to the flock may be low. If several ewes are affected, prevention becomes much more urgent.

For infectious causes, timing matters. Mosquito control, seasonal breeding management, and prompt diagnostic testing after abortions or congenital defects can help identify whether a virus such as Cache Valley virus may be involved. Good biosecurity also matters when introducing new sheep, especially because border disease can spread through infected animals.

Environmental prevention includes keeping pregnant ewes away from known teratogenic plants when possible and reviewing pasture conditions, hay sources, and feed changes with your vet. If an inherited defect is suspected, avoid repeating the same mating until the cause is clearer. In some flocks, culling affected breeding lines may be part of the long-term plan.

The most practical step is to submit diagnostic samples early. A confirmed cause can shape breeding decisions, vector control, quarantine practices, and expectations for future lamb crops.