Cerebellar Hypoplasia and CNS Malformations in Lambs: Tremors, Incoordination, and Poor Viability

Cerebellar hypoplasia is a congenital condition where the cerebellum does not fully develop before birth. The cerebellum helps control balance, coordination, and smooth movement, so affected lambs often look shaky, unsteady, or overly exaggerated in their movements. In lambs, this problem is usually present at birth or becomes obvious as soon as they try to stand and walk.

The term CNS malformations is broader. It includes abnormal development of the brain or spinal cord, such as cerebellar hypoplasia, cerebellar dysplasia, hydrocephalus, hydranencephaly, porencephaly, and microcephaly. These defects can lead to tremors, weakness, poor nursing, low viability, and failure to thrive. Some lambs have mainly movement problems, while others also have dull mentation, blindness, or severe weakness.

One well-known syndrome in sheep is border disease, sometimes called hairy shaker disease. Merck Veterinary Manual notes that affected lambs may be undersized, poorly viable, tremorous, and have an unusually hairy birth coat. In severe cases, cerebellar hypoplasia and other brain malformations can be present. Because several congenital and infectious conditions can overlap, your vet usually needs to look at the whole picture rather than one sign alone.

The most important cause to rule out is in utero infection, especially border disease virus, a pestivirus of sheep. Merck Veterinary Manual describes border disease as a congenital disorder associated with low birth weight, poor viability, tremor, and an excessively hairy birth coat. It can also cause cerebellar hypoplasia, cerebellar dysplasia, and more severe defects such as hydrocephalus, hydranencephaly, porencephaly, or microcephaly.

Not every shaky lamb has border disease. Other congenital neurologic problems can be inherited or can result from abnormal fetal development. Merck also notes that delayed myelination or hypomyelinogenesis can cause severe head and body tremors in newborn lambs. In addition, copper deficiency during pregnancy can cause congenital neurologic disease in lambs, often called swayback, which may lead to weakness, tremors, blindness, deafness, or inability to stand.

Toxins and management factors may also contribute in some species, although they are less commonly documented in sheep than infectious and nutritional causes. Because several conditions can look alike in the field, your vet may consider the dam's nutrition, mineral program, vaccination and biosecurity history, exposure to new animals, abortion history, and whether multiple lambs are affected in the flock.

Diagnosis starts with a careful history and physical exam. Your vet will want to know the lamb's age at onset, whether signs were present at birth, whether the lamb can nurse, and whether other lambs are affected. A neurologic exam helps localize the problem, but congenital brain disease can overlap with weakness from sepsis, starvation, trauma, or metabolic disease in newborns.

If border disease is suspected, Merck notes that clinical findings can be strongly suggestive, especially when tremors and poor viability occur with a hairy birth coat. Testing may include viral antigen detection on blood, flock-level investigation, and in some cases submission of tissues from a dead lamb for diagnostic lab work. Necropsy can be very helpful because severe cases may show cerebellar hypoplasia or other brain malformations. In the U.S., published veterinary diagnostic lab fees for lamb necropsy commonly fall around $150-$285, with added costs possible for histopathology, shipping, and special testing.

Your vet may also recommend mineral assessment when copper deficiency is on the list of possibilities. In some referral settings, advanced imaging such as MRI can identify cerebellar malformations antemortem, but this is uncommon in production sheep because of logistics and cost. In practice, diagnosis often combines exam findings, flock history, lab testing, and sometimes postmortem confirmation.

Prevention depends on the cause. For infectious cases, flock biosecurity matters most. Border disease is introduced by infected sheep and can also involve persistently infected animals, so your vet may recommend testing suspect animals, isolating additions, avoiding commingling with animals of unknown status, and investigating abortion storms, poor fertility, or clusters of weak shaker lambs. If one affected lamb appears, it is worth stepping back and looking at the whole flock.

Nutrition during pregnancy is also important. Merck notes that congenital neurologic disease related to copper deficiency can be prevented by treating affected ewes during pregnancy. That does not mean giving copper blindly. Sheep are sensitive to copper imbalance, and too much can be dangerous. The safest plan is to work with your vet on forage testing, ration review, and a sheep-appropriate mineral program.

Breeding and recordkeeping help too. Track which ewes produce affected lambs, note any abnormal coats, tremors, stillbirths, or poor viability, and save tissues from fresh deaths when your vet advises submission. Good records can reveal whether the pattern points toward infection, nutrition, or a possible inherited problem. Early investigation often costs less than repeating the same losses next season.