Studies on magnesium in ruminant nutrition

A relationship exists between the mineral composition of spring pasture and the occurrence of grass tetany.Both Kemp & 't Hart (1957) in Holland and Butler et al. (1963) in Scotland found a positive correlation between the ratio, potassium content : calcium and magnesium content in herbage and the incidence of grass tetany.At present there is no information on the physiological significance of this ratio when such herbage is consumed by ruminants.Attempts to reproduce grass tetany in adult ruminant.. with normal diets supplemented with K salts have been unsuccessful (Pearson, Gray & Reiser, 1949; Eaton & Avampato, 1952).The possibility exists that the absolute amounts of the elements as well as this ratio of K:Ca and Mg in herbage is important in the aetiology of this condition.Unfortunately, there are no figures in the literature for the intakes of these elements by grazing ruminants in the spring or at other times of the year.Estimation of the amount of a herbage constituent eaten by a grazing ruminant presents many problems, the greatest of which appears to be selective grazing.However, for Mg, Ca and K, it is unnecessary to sample herbage as grazed, since the