Grass Tetany

Grass Tetany, a metabolic disorder of ruminants, has been recognized for about 100 years. Although the overall incidence is not high it is a spectacular disease which may result in several animals, which were apparently normal when last seen, being found dead in the field a few hours later. It is thus of considerable economic importance to the individual farmer. Because grass tetany is associated with the lay type of farming and particularly with the use of large amounts of fertilizer rather than with the more traditional type of permanent pasture farming, the disease is encountered mainly by the modern progressive type of farmer. As more and more poor quality land is improved by reseeding with grass strains low in magnesium, such as rye grass, and the use of fertilizers, it can be anticipated that the incidence of grass tetany will increase unless adequate steps are taken to prevent disease. It is only within the last 30 years that workers in the Netherlands associated the disease with a decrease in the amount of magnesium in the blood of affected animals. During this period much research work has been designed to provide an explanation of the disease. Although a great amount of information has accumulated and many of the factors which can increase or diminish the incidence of the disease are now known, the exact mechanism which causes it is still the subject of much discussion. One of the most active workers in this field has been Andre Voisin, and it is therefore very helpful to have a book compiled by him reviewing available knowledge obtained from both scientific investigations and practical experience. Cattle most frequently develop grass tetany soon after they are moved from a diet of hay and concentrates to rapidly growing young pasture. Such a change in diet frequently results in a decreased intake of magnesium which is often a contributory factor to the development of the disorder. One of the effects of heavy applications of fertilizer, particularly potash, to pasture is to decrease the magnesium content of the grass, and it has been clearly shown that such applications of fertilizer increase the incidence of grass tetany. On the other hand the application of magnesium salts to pasture decreases the incidence of the disease. Research work has shown, however, that other factors must also be concerned, because grass tetany can be produced following a change in diet which does not alter the dietary intake of magnesium. It is generally agreed that the animal cannot absorb magnesium as efficiently when fed a lush grass diet as when on a hay and concentrate diet. It would appear from this short description of the disorder that it could be avoided with efficient management. As is indicated, however, the decision as to what is efficient management will vary with the environment and conditions governing the keeping of the animals and hence a book which reviews the subject as widely as does this present volume by Voisin will prove invaluable to all who are interested directly or indirectly in grass tetany. Translated from the French by Catherine T. M. Herriott