Seizures in Cows: Causes of Convulsions and Fits in Cattle

Seizures are sudden bursts of abnormal electrical activity in the brain that cause involuntary movements or changes in awareness. In cattle, pet parents and producers may describe them as convulsions, fits, paddling, or sudden collapse with stiffening and jerking. A seizure is not a diagnosis by itself. It is a sign that something serious is affecting the brain or the cow's body chemistry.

In cows, seizures are often tied to an underlying metabolic or toxic problem rather than lifelong epilepsy. Merck Veterinary Manual notes that hypomagnesemic tetany, also called grass tetany, can cause hyperexcitability, muscular spasms, seizures, collapse, and death. Other important causes include polioencephalomalacia, lead poisoning, salt toxicosis, and less commonly infectious brain disease such as listeriosis.

Because cattle can injure themselves during a seizure, safety matters right away. Keep people clear of the legs and head, reduce noise and stimulation if possible, and avoid forcing anything into the mouth. Then contact your vet urgently so they can identify the cause and discuss treatment options that fit the cow's condition, food-animal status, and your goals.

One of the most important causes is hypomagnesemic tetany, also called grass tetany. This happens when magnesium levels drop low enough to make the nervous system overreact. Merck describes classic signs such as sudden excitement, bellowing, collapse, jaw chomping, frothy salivation, and severe paddling seizures. It is most often seen in lactating cattle on lush pasture or green cereal crops, especially when calcium is also low.

Another major cause is polioencephalomalacia (PEM), a brain disease in ruminants associated with altered thiamine status or high sulfur intake. Cows with PEM may show head pressing, stargazing, cortical blindness, ataxia, and then seizures. Lead poisoning is also high on the list, especially in curious young cattle that chew batteries, paint, or machinery debris. Merck reports that affected cattle can develop blindness, salivation, muscle tremors, jaw champing, and convulsions within 24 to 48 hours of exposure.

Less common but still important causes include salt toxicosis or water deprivation, low calcium around calving, brain infections such as listeriosis, severe fever or systemic illness, and trauma. In practice, your vet will usually think first about the cow's age, stage of lactation, diet, pasture conditions, access to water, possible toxin exposure, and whether other cattle are affected. Those clues often narrow the list quickly.

Diagnosis starts with an emergency exam and a careful history. Your vet will ask when the seizure started, whether the cow recently calved, what she has been eating, whether water access changed, and if there is any chance of exposure to batteries, paint, chemicals, or poor-quality silage. A neurologic exam can help localize whether the problem is mainly in the forebrain, brainstem, or related to a whole-body metabolic disorder.

Testing depends on what your vet suspects. For grass tetany, Merck notes that diagnosis is often based on typical signs, response to treatment, and confirmation of low serum or urine magnesium from samples taken before treatment. If PEM is suspected, diagnosis is often presumptive based on signs such as blindness and head pressing plus response to thiamine therapy. If lead poisoning is possible, whole-blood lead testing can confirm it in a live animal, while liver or kidney testing may be used after death. Salt toxicosis is investigated with history, hydration status, and electrolyte testing.

In some cases, your vet may recommend bloodwork, cerebrospinal fluid testing, feed or water analysis, or necropsy if the cow dies. Necropsy can be especially valuable in herd situations because it may identify a preventable feed, mineral, water, or toxin problem affecting other cattle. That information can protect the rest of the herd and guide the most practical next steps.

Prevention depends on the underlying cause, but many seizure emergencies in cattle are linked to management factors your vet can help you review. For grass tetany, Merck recommends giving at-risk cattle access to a supplement with relatively high magnesium content before and during danger periods. This is especially important for lactating cows grazing lush spring pasture or green cereal crops. Consistent mineral intake matters more than offering a product that cattle barely consume.

Feed and water management also play a big role. Reduce sudden ration changes, review sulfur levels in feed and water if PEM is a concern, and make sure cattle always have reliable access to fresh water. Salt toxicosis becomes much more likely when waterers fail, freeze, or become crowded. If you feed silage, ask your vet to help assess quality because spoiled silage is a classic risk factor for listeriosis.

Finally, walk pastures, lots, and fence lines for toxin hazards. Remove batteries, peeling paint, old machinery, treated wood, and other lead sources. If one cow has seizures and the cause is unclear, involve your vet early rather than waiting for a second case. A prompt herd-level review can be one of the most cost-effective ways to prevent additional losses.