For cows diagnosed with grass tetany, prompt treatment usually gets the affected cow back on her feet. Unfortunately, the first symptom of grass tetany may be a dead cow that appears to have struggled.

Most cases of grass tetany occur from January to April during periods of stressful weather changes, especially when it's cool, damp and cloudy. Grass tetany is caused by low magnesium (Mg) in the blood. When blood serum magnesium is low, the symptoms, such as not eating right and not producing adequate milk, are sometimes hard to see, according to Ryan Lock, a graduate student studying the problem at the University of Missouri. In acute cases of grass tetany, the magnesium in the blood serum is so low that the cow's body takes magnesium from the cerebrospinal fluid, which can lead to paralysis, coma and even death.

Mr. Lock noticed that magnesium concentration are typically at their lowest levels in tall fescue during the early spring-a time when many cows are beginning lactation and require nearly three times more magnesium per day to produce milk. Researchers believe magnesium levels are lower at this time because plants may not be picking up the needed magnesium necessary from the soil, especially if soil phosphorus levels are low. Mr. Lock drew on previous MU research that indicated phosphorus applications increase the level of magnesium in tall fescue.

At MU Southwest Research and Education Center near Mount Vernon, Mo., Mr. Lock is conducting research to determine if phosphorus applications to pastures can increase magnesium uptake in fescue and increase Mg intake by cattle. He grazed three groups of cattle in separate pastures for 56 days.

The experiment indicates that tall fescue in pasture with 30 pounds per acre of available phosphorus provided the same protection against grass tetany as supplying free-choice magnesium supplement.