Cattle Death from Grass Tetany

Summary

The rapid rise of potassium in the leaves of grasses occurs when air temperatures of 8C (night) and 16oC (day) last for four to six consecutive days on soils where temperatures of 6oC to 7oC have been sustained for at least a week. Under these conditions plant roots (grasses and cereals) change from passively absorbing to actively absorbing potassium (K). As a result, high levels of K become available in the leaves of the plants. Soils with high levels of K will be more dangerous than soils with a better balance of K compared to calcium (Ca) and magnesium (Mg). New grass shoots on dangerous soils will also have inordinately high levels of K. The same process occurs in legumes, but the K/Mg and Ca does not rise as dramatically because the legumes have naturally higher levels of Ca and Mg. Cattle under stress from lactation, mustering or first oestrous during cold weather immediately after warm weather need critical amounts of Mg to sustain normal physiological functions. Cattle can ingest plants containing high levels of K, which will effectively cut Mg absorption in the rumen, leading to an acute Mg deficiency, which in turn leads to death from grass tetany.