Congenital Tremor in Lambs: Why Newborn Sheep Shake

Congenital tremor is a condition present at birth that causes a newborn lamb to shake, wobble, or have rhythmic muscle tremors. In sheep, these tremors are often most obvious when the lamb tries to stand, walk, or nurse. Some lambs also look small for their age, seem weak, or have a rough, overly hairy fleece at birth.

One of the best-known causes is border disease, sometimes called hairy shaker disease. This happens when a ewe is infected during pregnancy with a pestivirus that affects the developing fetus. The virus can interfere with normal nervous system development, including myelin formation, which helps nerves send signals smoothly.

Not every shaking lamb has the same problem, though. Tremors in a newborn can also be confused with weakness from hypothermia, low blood sugar, infection, birth trauma, or other neurologic disease. That is why a hands-on exam matters. Your vet can help sort out whether the lamb has a congenital condition, an infectious disease, or another urgent problem that needs different care.

The outlook varies. Some mildly affected lambs improve as they grow and their tremors gradually fade over a few months. Others have trouble nursing, staying warm, or thriving, and those lambs need closer monitoring and more support.

In sheep, the most recognized cause of congenital tremor is border disease virus, a pestivirus that infects the fetus during pregnancy. Lambs affected before birth may be born undersized, weak, tremoring, and with the classic rough or hairy fleece. Some surviving lambs can remain persistently infected, which matters for flock health because they may continue shedding virus.

The virus is often introduced when a flock adds infected sheep or pregnant ewes carrying infected fetuses. Sheep may also be exposed through contact with infected cattle, because closely related pestiviruses can cross between species. In a flock outbreak, pet parents may notice more barren ewes, abortions, stillbirths, or weak lambs around lambing season.

Not every newborn that shakes has congenital tremor from border disease. Your vet may also consider hypothermia, low blood sugar, septicemia, meningitis, birth injury, toxic exposure, or less common congenital brain and spinal cord disorders. These problems can look similar in the first hours of life, especially when a lamb is weak and chilled.

That is why the cause matters as much as the symptom. A lamb with a true congenital neurologic problem may need supportive care and flock-level disease control, while a lamb with low blood sugar or infection may need urgent warming, feeding support, and other treatment right away.

Diagnosis starts with a careful history and physical exam. Your vet will want to know when the tremors began, whether the lamb can stand and nurse, if the fleece looks unusually hairy, and whether there have been abortions, stillbirths, or other weak lambs in the flock. The timing matters because congenital tremor is present at or very soon after birth, while some other neurologic problems develop later.

On exam, your vet will assess body temperature, hydration, suck reflex, coordination, and signs of infection or trauma. In many cases, the first priority is not a lab test. It is stabilizing the lamb with warmth, colostrum or milk support, and monitoring for pneumonia or dehydration.

If border disease is suspected, your vet may recommend flock-level investigation and diagnostic testing. Depending on the case, that can include PCR or other laboratory testing on blood or tissues, plus necropsy and histopathology if a lamb dies. Clinical signs can strongly suggest border disease, but testing helps confirm the diagnosis and guide prevention steps for the rest of the flock.

Because several serious newborn problems can mimic congenital tremor, diagnosis is often about ruling out emergencies while building the bigger flock picture. That is especially important when multiple lambs are affected or when breeding animals were recently introduced.

Prevention focuses on flock biosecurity and breeding management. Because border disease is a major cause of congenital tremor in lambs, the most important step is reducing exposure of pregnant ewes to infected animals. Work with your vet before adding new sheep, and be cautious about mixing sheep with cattle that may carry related pestiviruses.

Quarantine and test new additions when your vet recommends it, especially if they come from a flock with unknown reproductive history. If your flock has had hairy shaker lambs, abortions, or unexplained weak newborns, your vet may advise testing affected lambs and reviewing whether any animals could be persistently infected. Removing infection sources is often more important than treating individual cases.

Good lambing management also helps reduce confusion with look-alike emergencies. Make sure newborn lambs are dried promptly, kept warm, and receive adequate colostrum early. Weak lambs decline fast, and supportive care in the first hours can prevent secondary problems like hypothermia and starvation from making a congenital problem look worse.

There is no single prevention plan that fits every flock. A practical plan may include closed-flock practices, careful sourcing of replacements, separation from higher-risk animals, and a diagnostic workup when losses occur. Your vet can help build a prevention strategy that matches your flock size, goals, and budget.