Sheep walk in circles most commonly because of a bacterial brain infection called listeriosis, known in farming as “circling disease.” The bacteria damages one side of the brainstem, creating a neurological imbalance that drives the animal to turn repeatedly in one direction. Other causes include brain parasites and, rarely, inner ear problems. If you’re here because of the viral 2022 video showing a flock in China walking in a tight loop for days, that case is more complicated, and experts aren’t convinced it was disease at all.
Listeriosis: The Classic “Circling Disease”
The most well-known reason a sheep circles is infection with the bacterium Listeria monocytogenes. This organism lives in soil and decaying plant matter and thrives in poorly fermented silage, particularly when the pH rises above 5.5. Sheep ingest the bacteria while eating, and from there it takes an unusual route into the brain: it travels along nerve fibers, particularly the trigeminal nerve and other cranial nerves, migrating up the axons until it reaches the brainstem.
Once inside the brainstem, the bacteria creates tiny abscesses that destroy surrounding nerve tissue. In about 85% of infected animals, the damage hits one or more cranial nerve centers. The infection is almost always lopsided, hitting one side of the brainstem harder than the other. This asymmetry is what produces the circling. The sheep’s brain is essentially getting conflicting signals about balance and movement, and the animal turns toward the damaged side in a compulsive loop it cannot override.
Beyond circling, the signs of listeriosis are distinctive. One side of the face often goes slack: a drooping ear, a sagging eyelid, saliva dripping from limp lips. The sheep loses coordination, stops eating, and runs a fever. These symptoms tend to worsen rapidly. Without treatment, the fatality rate for brain-involved listeriosis approaches 100%. If caught early, while the sheep can still stand and swallow, antibiotic treatment saves roughly 77% of animals. Once a sheep becomes unable to stand or swallow, the outlook is grim: more than 90% at that stage die or must be euthanized despite treatment.
Brain Parasites That Cause Circling
A second cause of circling is coenurosis, sometimes called “gid” or “sturdy.” This disease comes from the larval stage of a tapeworm whose adult form lives in the intestines of dogs and wild canines like wolves and foxes. Dogs shed tapeworm eggs in their feces. Sheep grazing on contaminated pasture swallow the eggs, and the larvae hatch, enter the bloodstream, and migrate to the brain. There, they develop into fluid-filled cysts that slowly grow and press on brain tissue.
The chronic form is more common and produces a gradual onset of neurological problems. As the cyst expands, the sheep may tilt its head, lose coordination, become blind in one or both eyes, and circle. Unlike listeriosis, which tends to come on within days, coenurosis develops over weeks or months. Affected lambs in clinical studies showed extreme lethargy, weight loss, bilateral blindness, and repetitive head and neck movements. The circling in coenurosis results from physical pressure on the brain rather than bacterial destruction, but the outward behavior looks similar.
What About the Viral China Video?
In November 2022, footage from Inner Mongolia showed dozens of sheep walking in a tight, nearly perfect circle. The owner reportedly said the behavior had continued for 12 days. The video went massively viral, with speculation ranging from disease to doomsday prophecies. Veterinary experts were largely skeptical.
Emma Doyle, a sheep researcher, said the behavior looked “a bit dodgy” and possibly staged, noting that something appeared to have been placed in the center to prevent sheep from cutting across. The concentric pattern was far too neat for a natural behavior. Andrew Fisher, a professor of cattle and sheep production medicine at the University of Melbourne, pointed out that listeriosis typically affects 1 to 10 percent of a flock, not half of it. Sick sheep also don’t march in organized loops. They loll in irregular, individual patterns and quickly become too ill to keep moving.
The most grounded explanation was simply that one sheep started circling (possibly due to mild illness or confinement behavior), and others followed. Sheep are intensely social and will trail a leader without much independent thought, especially in a confined pen with little else to do. The animals were also clearly leaving the circle at times for food and water, since no sheep survives 12 days without either. The dramatic framing of the video obscured what was likely a much more mundane reality.
How Flocking Instinct Amplifies the Problem
Sheep have one of the strongest herding instincts of any domesticated animal. In open pasture, this keeps flocks together and moving as a unit, which helps with predator avoidance. In confined spaces, it can produce strange-looking behavior. If a dominant or centrally positioned sheep begins walking in a pattern, others will fall in behind it. This isn’t circling disease. It’s social following carried to an extreme in an environment where there’s nowhere else to go.
Stereotypic behaviors, repetitive movements with no obvious function, also appear in sheep kept in small enclosures with limited stimulation. Pacing along fences, circling within pens, and repetitive head movements can all develop in animals that are bored, stressed, or confined for long periods. A single sheep circling in a large pasture is far more likely to have a medical problem. A group doing it together in a pen is more likely exhibiting a social or environmental behavior.
Telling Disease From Normal Behavior
The key distinction is whether the circling comes with other neurological signs. A sheep with listeriosis will have facial drooping on one side, excessive drooling, a head tilt, loss of appetite, and a fever. It will deteriorate over hours to days. A sheep with coenurosis will show progressive weight loss, possible blindness, and increasing lethargy over weeks. In both cases, the animal is clearly unwell beyond just the circling.
A healthy sheep that circles briefly in a pen, especially if others are doing it too, is most likely responding to confinement, stress, or the social pull of the flock. The behavior typically stops when the animal is moved to a new environment or given more space. If circling persists when the sheep is alone and in open space, or if any facial asymmetry, drooling, or coordination loss appears, a neurological cause is far more likely.
Preventing Circling Disease in Flocks
Since listeriosis is the most dangerous and common medical cause of circling, prevention centers on feed management. Silage that hasn’t fermented properly, particularly with a pH above 5.5, is a prime breeding ground for Listeria. Ensuring silage is well-sealed, properly acidified, and free of soil contamination significantly reduces risk. Spoiled or moldy sections of silage bales should be discarded entirely rather than fed.
For coenurosis, prevention means breaking the parasite’s life cycle. Regular deworming of farm dogs, preventing dogs from eating sheep carcasses (which contain the larval cysts), and keeping dog feces off grazing pasture all reduce transmission. In regions where the tapeworm is common, these measures are a routine part of flock management.