Magnesium Oxide Contraindicated as a Cathartic for Cattle in the Absence of Rumen Acidosis

Abstract

Cathartics are chemicals that promote defecation. Saline cathartics are salts of poorly absorbed ions for example the cation magesium or the anions sulphate, phosphate, tartrate or citrate. Although these chemicals are not absorbed from the intestine they are osmotically active and attract and retain fluid within the intestinal tract and in this way promote defecation. Saline cathartics that are commonly used in cattle practice include magnesium sulphate (Epsom salts), sodium sulphate (Glauber's salts), magnesium oxide and magnesium hydroxide. These latter two compounds are primarily used as antacids in the treatment of rumen acidosis but they also have a cathartic effect. In fact, magnesium oxide and magnesium hydroxide are ideal chemicals for the treatment of grain overload in cattle. The combination of antacid activity which neutralizes excess acid in the rumen and cathartic activity which stimulates passage of toxic material out of the digestive tract is very beneficial. Tables I and 2 list some commercially available antacids for use in ruminants for the treatment of grain overload or acid indigestion. Generally, the powders contain magnesium oxide as the active ingredient or a mixture of magnesium oxide and magnesium hydroxide. Boluses, on the other hand usually contain magnesium hydroxide. Although these compounds are very efficacious as antacids in the treatment of grain overload, a problem associated with their use has recently been noted at O.V.C. A number of adult cattle have, at presentation, exhibited a profound metabolic alkalosis with no detectable abomasal abnormality. A frequent history in these cases has been the prior administration via stomach tube or by drench bottle of magnesium oxide or magnesium hydroxide as a cathartic or rumen stimulant for the treatment of acute or chronic anorexia. Invariably these compounds have been administered as one of the aforementioned commercially available antacid products. Accordingly, several questions arose as a result of these baffling cases.