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Cattle producers need to keep winter tetany in mind

by Wyoming Livestock Roundup

While many producers are aware of grass tetany, an issue generally occurring in the spring when cattle or sheep are turned out on lush grass or annual cereal forages such as rye, wheat and/or tritcale, University of Nebraska-Lincoln (UNL) Extension Specialists Aaron Berger and Mary Drewnoski remind producers of the threat of winter tetany in upcoming months.

            During an episode of UNL’s Beefwatch pocast, Berger explains grass and winter tetany are common names for hypomagnesaemia, a metabolic disorder related to a deficiency of blood magnesium. 

            “Magnesium is critical for proper nervous system and muscle function,” states Drewnoski, noting cattle with low magnesium may exhibit hyper-excitability, reduced feed intake and muscle twitching, while also appearing to be uncoordinated and walk with a stiff gait.

            “Recent forage test results have indicated winter tetany could be a potential issue this year with some of the hay that was harvested this fall,” Berger adds.

Mineral levels

            Contrary to what many producers may believe, Drewnoski explains winter tetany does not always occur as a result of low magnesium levels in forages fed throughout the winter. Instead, the condition usually occurs when animals are fed forage with high amounts of potassium. 

            “High levels of potassium can cause low magnesium levels because it interferes with the absorption of magnesium,” notes Drewnoski. 

            She further notes levels of potassium at or greater than two percent are cause for concern.

            “When hay is low in magnesium – less than 0.15 percent – and also low in calcium – less than 0.4 percent – while being simultaneously high in potassium – greater than two percent – tetany is likely to occur,” she states. “Forages likely to cause tetany are often borderline to low in magnesium, with excess levels of potassium. Usually, these forages also tend to be low in sodium content.” 

            According to Drewnoski, sodium is important in this situation because the mineral is critical in transporting magnesium into cells. Therefore, providing adequate sodium is critical to reducing the incidence of winter tetany. 

Preventing winter tetany

            In order to prevent winter tetany from occurring, Berger and Drewnoski provide a few tips for producers.

            First and foremost, the two believe testing hay for mineral concentrations is critical to identify if an imbalance of magnesium, potassium and calcium is present. 

            “If hay tests low in magnesium and calcium but high in potassium, producers should consider feeding a high calcium, high-magnesium mineral supplement containing salt,” says Berger.

            Drewnoski notes the most common magnesium supplement fed to cattle is magnesium oxide, which is bitter and unpalatable. 

            “We can definitely overcome this,” she says. “In fact, producers can add dried distillers’ grains or soybean meal at the rate of one to 50 pounds of the mineral and salt mix to help increase palatability and intake.” 

            “In instances where cattle are being hand fed a protein or energy supplement, supplemental magnesium can also be delivered with the feed,” Drewnoski continues. “If this occurs, make sure access to loose salt is also provided.” 

            Additionally, Berger and Drewnoski encourage producers to examine the concentration of potassium in the mineral supplements they use. 

            “If feeds are already high in potassium, feeding additional potassium in a mineral only aggravates the problem,” states Drewnoski. 

            Another option to consider when managing forages high in potassium and low in magnesium, according to the two specialists, is to simultaneously feed hay higher in calcium and magnesium. 

            “Winter tetany can be an unexpected problem as most producers are not looking for it this time of year,” Berger concludes. “Through forage testing for levels of calcium, potassium, phosphorus and magnesium present, producers can determine if action may be needed to prevent winter tetany from occurring.” 

            Hannah Bugas is the managing editor of the Wyoming Livestock Roundup. Send comments on this article to

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