PREVENTION OF HYPOMAGNESAEMIA AND GRASS TETANY

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Abstract
SUMMARY: A seasonal hypomagnesaemia, sometimes accompanied by a hypocalcaemia, was demonstrated in beef cattle at pasture and receiving supplementary hay in North‐East Victoria.An effective method of prophylaxis under extensive grazing conditions was developed. This consisted of mixing a cheap magnesium oxide supplement with water and spraying it on a small percentage of the hay ration, which was then fed to stock before the remainder of the hay was made available.Results from 1961‐63, showed that a dose of 2 oz/cow/day of magnesium oxide significantly raised serum magnesium levels. A dose rate of 4 oz/cow/second day appeared to be equally effective, but there was little evidence to support the use of 4 oz/cow/third day.The data also suggested that the magnitude of the response to magnesium supplementation depended on the initial level of serum magnesium in the susceptible stock.The practice of feeding magnesium oxide either daily or every second day to cattle and sheep during the grass tetany danger period has become widespread in Victoria since 1961. Losses on affected properties since feeding was initiated have been negligible.