Addressing grass tetany in beef cows

The Daily Ardmoreite
Leland McDaniel

The following comments are courtesy of Barry Whitworth, DVM Area Food/Animal Quality and Health Specialist for OSU Extension, discussing grass tetany. Grass tetany is a common malady of nursing cows grazing lush forages, such as wheat pasture.

While I was in practice, the months of February and March were the most common time of the year to see grass tetany in cattle. A common scenario was a cool season forage heavily fertilized. The cattle were standing knee deep in dark green grass. Cows were either late bred or in early lactation. Following a cold wet night, a producer would find a dead or down cow in the pasture. If this sounds like something that you might encounter, a review of grass tetany may be helpful.

Grass tetany which is also known as hypomagnesemia, grass staggers, or wheat pasture poisoning is a serious and often fatal metabolic disease that occurs in cattle and less commonly in sheep and goats. The disease is caused by low blood and cerebral spinal fluid levels of magnesium. Magnesium is important because it is involved in hundreds of bodily functions. Without this mineral, cells are unable to produce energy, muscles constantly contract, and nerves cease to respond in a normal manner. Magnesium also plays a role in electrolyte balances in the body. These are just a few of the body functions that are affected when magnesium falls below normal levels in the body.

The disease most commonly affects older cows in early lactation, but it may also occur in cattle of any age or sex. It is typically a late winter or early spring problem coinciding with the rapid growth of cool season grasses. It occurs most commonly when cattle are grazing lush immature grass such as cereal grains, fescue, or rye grass which are low in magnesium. Poor weather conditions may also play a role in cattle getting the disease if it interferes with food intake. Short periods of starvation may cause sudden drops in calcium and magnesium levels which results in the clinical signs of grass tetany. Soils that are heavily fertilized with nitrogen, potassium, or chicken litter may also cause problems. When nitrogen and potassium levels are high in the rumen, magnesium is poorly absorbed. All the above conditions mentioned may contribute to grass tetany, but an emphasis should be placed on watching cows when they are early in lactation grazing lush green pastures during inclement weather.

Clinical signs of grass tetany vary depending on how early in the disease process cattle are noticed. Many producers do not know there is a problem until they find cattle dead with evidence of thrashing or a cow down. Early signs of the disease include incoordination, a hypersensitivity to touch or sound, frequently urination, and muscle tremors. As the disease progresses, the cattle will have convulsions followed by coma and death.

Diagnosis of the disease is usually based on response to treatment. However, blood or urine samples can be evaluated for magnesium levels. In suspicious dead animals, veterinarians can submit the eye for analysis.

Treatment of the disease requires Intravenous (IV) or subcutaneous (SQ) injections of magnesium or oral supplements of magnesium. Most veterinarians will administer a solution that contains calcium and magnesium since symptoms of grass tetany are similar to milk fever. Also, it is common to have low levels of both minerals with grass tetany. If cattle respond to the IV or SQ injections, veterinarians will recommend follow up treatments with an oral supplement. Producers need to remember that even with the best of care some cows will not respond to treatment.

Preventing grass tetany is much more rewarding than treatment. Since cattle do not store magnesium, they must have a daily source. In conditions that are susceptible to low magnesium levels such as lush green pastures, magnesium should be provided in the feed or a mineral supplement. Magnesium is not very palatable, so producers need to monitor intake. Since cows in early lactation are the most susceptible to the disease, it may be a better option to graze steers, heifers, dry cows, or cows with older calves on susceptible pasture. It is possible to reduce the danger of pastures susceptible to grass tetany by adding legumes, fertilizing based on a soil analysis, and top dressing the pasture with magnesium. As mentioned above, cattle tend to fall victim to the disease following inclement weather because they tend to be stressed and eat less, so providing shelter and feed and hay should aid in preventing the disease. Adding hay to the diet may help prevent the disease because mature forages tend to have higher concentrations of magnesium. These suggestions may not eliminate the potential of grass tetany but incorporating them should lower the risk.

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