Attempts to produce hypomagnesaemia in dry non-pregnant sheep

Summary

Dosing urea or ammonium acetate (up to 11 g ammonium nitrogen equivalent) failed to lower serum magnesium or calcium in wethers fed a ration of dried grass. This level of dosing raised blood non-protein nitrogen by 4–14 mg%, and was sufficient to cause inappetance within several days.

Serum magnesium of three groups of sheep which had been fed in sheltered pens on fresh grass, dried grass, and dried grass plus ammonium acetate respectively fell within one day after the sheep were turned out to spring pasture, but were normal on the fourth day of grazing.

When sheep that had been free grazing were starved in sheltered pens, serum magnesium rose within one day but had returned to the original level after four days. Serum calcium showed successive falls during this time.

Linear falls in serum magnesium and calcium were produced when sheep, both in lean and in fat condition, were starved for several days in a pen exposed to the weather. When the sheep were let out to pasture again, serum calcium returned to normal in three days but serum magnesium fell still further and was still low after four days.

Acute hypomagnesaemia without accompanying hypocalcaemia was not produced by under-nutrition or starvation; it is concluded that the observed changes in magnesium levels were associated with the change from pens to pastures.