Grass Tetany (Hypomagnesia) is a nutritional disorder involving the deficiency of the mineral magnesium in the blood stream. The cause is complex as often other minerals, most commonly calcium and potassium, are also out of ratio.

This deficiency causes weakness of the muscles and symptoms show muscle twitching, poor coordination, highly alert, stiff gait, convulsions and death due to failure of the respiratory system, however often cows are simply found dead. There are many causes of hypomagnesia but livestock are commonly affected when feeding on lush or fast growing pasture, however there may be many other factors involved such as the use of high nitrogen or potassium fertilizer, the stage of growth the pasture is at, as well as the species of crop, stress, scouring, cold wet weather and high milk production.

Grass Tetany affects all ruminants. Lactating cows or cows with a calf in winter and early spring are most at risk of succumbing to hypomagnesia. Magnesium is unable to be stored by the body, so the animal’s daily requirement must be available in the feed or in supplements.

Treatment is required urgently to restore blood magnesium levels to normal, injection packs are given under the skin.

Picture from: http://solutionsforyourlife.ufl.edu/hot_topics/agriculture/grass_tetany.html