Grass tetany can affect lactating ewes in the spring when ewes are allowed to graze rapidly growing or lush pasture. The disorder can occur any time there is an abrupt change to lush, rapidly growing forage, especially after irrigation and heavy nitrogen fertilization. Grass tetany is characterized by too little magnesium in the blood, but a low blood calcium level also may be present. Low magnesium concentration in the feed is usually a factor in the development of grass tetany, but the disease can occur even if the feed is not deficient in magnesium.

Affected sheep become separated from the flock and show muscular tremors, nervous excitement, and a staggered or stiff gait. Finally, they go into convulsions. The animal may appear intoxicated. Death usually occurs within a few hours. Attacks can be brought about by the excitement associated with moving or working sheep. Lactating and older ewes are most often affected.

If sheep are grazing early growth of cereal grains or heavily fertilized pastures, provide supplemental magnesium. Feeding dry alfalfa hay to penned ewes at night aids in preventing the disease. Magnesium oxide at the rate of 0.25 ounce per head per day can be mixed with grain or provided in pelleted rations. A mineral mix containing 16 percent magnesium oxide provided in the corral or loafing area also may be effective.