Stock farmers should all be aware of the problems that staggers (hypomagnesaemia or grass tetany) causes in cows when cattle are turned out on fresh grass in the spring.

In cattle, symptoms usually occur around calving. This usually coincides when the uptake of Magnesium in the plant is supressed in preference to taking up Potassium.

Because Magnesium plays a key role in the function of the central nervous system, the animals are prone to muscle tremors, staggering and collapse and / or poor appetite and reduced milk yield. In acute cases in older cows, or on low magnesium soil, grass symptoms can occur in as little as three to four days.

Grass Tissues
The tissue test above was taken from a Clay Loam soil that has a naturally high Magnesium content. Farmers beware! This situation often happens after periods of high rainfall, and then drought. Similar to the winters of 2018-19 & 2019-20.

The ionic weight of Magnesium is smaller than that of Calcium and Potassium and is therefore comparatively mobile in the soil solution. But because Magnesium is hygroscopic its hydrated radius is much larger than normal during periods of high rainfall. Therefore, mass flow to plant available nutrition will be high.

But this mass flow also results in significant volumes of Magnesium leached out of the soil in the autumn and winter as a result of a high positive water balance. Conversely, in periods of drought the transport of Magnesium to the roots is significantly impaired. Hence the results of the tissue test.

Another problem often associated with flooding and waterlogging is a compromised soil mineral delivery system due to damaged soil structure adversely affecting the root’s ability to absorb nutrients from the soil. One significant affect of this adverse weather is that Phosphorous is rendered unavailable causing a loss of fertility, or even milk fever.

Plus, with waterlogging grass can be low in Zinc which adversely affects foot health and the renal system in ungulates.

A further problem (below) is that the plant absorbs abnormally high levels of Molybdenum, or even Iron.

When stock graze on grass that is excessively high in Molybdenum, the animals are unable to absorb Copper.

Tissue grazing

Symptoms in ruminants, and often horses, of copper deficiency include changes in the coat structure and appearance, a loss of appetite and scouring. In severe cases young animals can develop bone fractures.

It is always worthwhile taking tissue tests to confirm how forage is interacting with the soil for the benefit of your animals. My experience is that weather patterns often produce unexpected results in forage that are contrary to the soil analysis results.

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