The underlying problem is a shortage of magnesium both in the cattle and in their diets. High levels of plant potassium and nitrogen both interfere with magnesium absorption by the animals. Therefore, fertilization with potash and/or ammonium sulfate can increase plant growth and also increase the risk of Grass Tetany. The demands of lactation deplete the cow of both magnesium and calcium and the clinical signs are caused by the combined shortage of magnesium and calcium in these cattle. In addition to low magnesium intake combined with higher levels of potassium and ammonia, cattle that are consuming low levels of calcium, phosphorus, and salt are at greater risk of developing Grass Tetany.
When cattle are found dead, there is most often a sign of a struggle. Generally, grass and dirt has been disturbed by the animal’s feet and head where they had thrashed about. If located while still alive, the cattle will be seen having convulsions, weakness, and disorientation. They may also become belligerent and attack objects, or people. Symptoms of Grass Tetany are often confused with Rabies, Listeriosis, or a number of other conditions that affect the brain or can cause sudden death.
A diagnostic problem has existed for some time, because many cattle are simply found dead and tissue and serum magnesium levels can return to normal at or near death. However, it has ben shown that the magnesium concentration of fluid within the eye does not fluctuate upwards near death, so this material can be collected for many hours after death and analyzed for magnesium content. The magnesium concentration of this fluid can be easily interpreted to determine if the cow dies of Grass Tetany. Your veterinarian can also collect cerebrospinal fluid in cases where the eyes are not available due to predation, and these samples can also be analyzed for magnesium content.
Dr. John Maas, University of California Extension Veterinarian recommends the following: If live cattle are thought to be at risk for Grass Tetany, serum samples can be collected and analyzed for magnesium. However, if Grass Tetany is highly suspected, you and your veterinarian should plan carefully the collections of these blood (serum) samples, as the simple act of running the cattle through a chute can precipitate life-threatening convulsions. By either method, appropriate samples can be collected, analyzed, and accurately interpreted to decide if Grass Tetany is the cause of the problem.
Treatment of Grass Tetany is often accomplished by intravenous solutions of magnesium calcium. Treatment of sick animals can be very frustrating, and recovery does not occur in all cases. In addition to intravenous therapy, 2 ounces of magnesium chloride or magnesium sulfate can be given in 200 ml warm water as an enema. The blood magnesium levels will increase 20 minutes after the enema. This can be particularly helpful in cows that are down and convulsing or belligerent. To prevent relapses in cows treated under range conditions, it has been recommended to give oral slurries of 3 ounces of magnesium oxide plus 3 ounces of dicalcium phosphate and 1 ounce of salt in 1-2 gallons of water. This can be difficult because many of these cattle are not cooperative patients. Any treatment decisions should be carefully discussed with your veterinarian prior to implementation as individual products vary widely with respect to effectiveness and safety.
Prevention is the key to successfully handling this condition, as therapy is oftentimes not rewarding. The main goals of prevention are to achieve increased consumption of magnesium and calcium through supplementation. There are a number of ways this can be accomplished. Salt-mineral mixes and molasses licks or blocks are the most common methods that are successful. Some homemade recipes are:
1. 1:1 magnesium oxide : molasses (free choice)
2. 1:1:1:1 magnesium oxide : salt : dicalcium phosphate : corn meal (4 ounces per head per day, minimum, mix-add more corn meal [soybean meal, etc.] if less)
The main dietary goal is to supplement 1-2 ounces of magnesium oxide (or magnesium sulfate) and 1-2 ounces of dicalcium phosphate or other calcium source per animal per day. Any method that will get this done is a good method.
The statement that "an ounce of prevention is worth a pound of cure" certainly holds true for Grass Tetany.