Grass tetany is a condition that can develop when cattle graze lush pastures. The disease is also known as grass staggers, wheat pasture poisoning, magnesium tetany, and hypomagnesia. It is more common in cows in heavy lactation and is caused by low levels of magnesium in the blood. When blood magnesium is too low, proper nerve impulse transmission fails, causing the disorder. High levels of nitrogen (protein) and potassium can reduce availability of magnesium in the forage, which exacerbates the problem. Consequently, the problem can be more common when animals are grazing fertilized pastures.
Affected animals tend to be excitable and may appear blind. Animals may be observed grazing away from the main herd, have muscular twitching in the flank, appear wide-eyed, have muscular incoordination, and have a staggering gait. Ultimately, they will collapse, thrash about, enter a coma, and eventually die. In some cases, symptoms of grass tetany are never observed. The animal is simply found dead.
Treatment is difficult due to the rapid onset of the condition. In some cases, your veterinarian can administer an intravenous infusion of calcium and magnesium in a dextrose solution with positive results.
Your best bet is to take steps prior to grazing to avoid grass tetany. There are many commercial mineral mixes designed to provide adequate magnesium to prevent grass tetany with the most common source being magnesium oxide. Keep mineral boxes filled and scattered at several pasture locations. To be effective, the mineral mix should contain at least 10 percent magnesium. Magnesium oxide is unpalatable and generally needs to be mixed with other supplements to encourage consumption.
