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Risk of Magnesium Tetany in Outwintered Cows

Published Wednesday, 13th January 2016 in Veterinary Services news

Snowy Highland Cow

SRUC experts are alerting farmers that in light of this winter’s extreme weather, there is an increased risk of their cows suffering from magnesium deficiency.

The condition is commonly known as grass staggers and often affects grazing cattle in spring, but magnesium tetany can also affect overwintered cows fed on silage.  

“The condition leads to hyper-excitability, muscular spasms, convulsions, respiratory distress, collapse, and even death,” says Veterinary Investigation Officer George Caldow of SAC Consulting, part of SRUC. “Magnesium is essential for metabolism and the requirement increases at times of stress. Furthermore cattle rely on a steady intake of magnesium and heavy rainfall can interfere with the normal food intake of cows so that magnesium intake becomes critical.”

Most farmers have responded to the recent appalling weather by ensuring their often dry, pregnant spring calvers, are well fed with big bale silage. Normally this is more than adequate to meet a cow’s energy requirements and to allow her to cope with the conditions but can often be insufficient to meet the cow’s specific requirements for some vital minerals and vitamins.

“Although cattle are well designed to withstand very low temperatures, they are less well adapted to continuous rain which is what they have had to face over the last four – five weeks,” comments George Caldow.

“This continual drain on their heat reserves when coupled with a deficiency of magnesium can result magnesium tetany.  While all producers are well aware of the risk of tetany to cows suckling calves at grass in the spring, it is not commonly expected in the middle of winter! Our advice is therefore for all producers with outwintered stock, particularly cows, to ensure they are adequately supplemented with a suitable magnesium supply daily.”

For further information please contact George Caldow on 01835 822 456, or at

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