Investigations into the use of supplements for the control of hypomagnesaemia in dairy cows during the spring grazing period

1. Three experiments are described on the feeding of supplements of calcined magnesite, linseed cake and vitamin D to dairy cows for the control of hypomagnesaemia and the prevention of hypomagnesaemic tetany on spring pastures. 2. A daily supplement of 2 oz. calcined magnesite either contained in 2 lb. of dredge corn cubes or 4 lb. dredge corn mix, or as a drench, gave adequate protection against the development of hypomagnesaemia in the fifty-six cows to which it was given. 3. The supplements of 3½–4 lb. linseed cake and 12,500 i.u. vitamin D gave only partial protection. 4. The economics of providing dairy herds with magnesite during the early grazing period is discussed.