Management Factors and Grass Tetany in Dairy Cattle

The relationship between intensity of production and the occurrence of hypomagnesaemia and grass tetany in dairy cattle was investigated from 1966-1970 at the Ellinbank Dairy Research Station, Warragul, Victoria. Hypomagnesaemia and/or grass tetany occurred in cows grazing at both high (3.2 cows/hectare) and low (2.2 cows/hectare) stocking rates over the four-year period. Pasture Mg concentrations remained relatively high (0.2% dry matter) throughout this period, except in the low stocking rate pastures in one year, 1967. It is concluded that hypomagnesaemia and grass tetany was precipitated by a combination of low dry matter intake in winter and the effects of a gradual increase of K concentration in autumn and winter pastures, following the heavy application of K fertilizer. Under these conditions, MgO supplementation was inadequate to prevent grass tetany occurring in some animals.