University of Nebraska Extension Beef Educator Aaron Berger and Beef Systems Specialist Mary Drewnoski warn cattlemen not to forget about grass tetany during winter feeding. Although this condition is most commonly associated with springtime when livestock are turned out to pastures on cool-season forages, tetany can also occur during the winter as cattle are fed grass hay, alfalfa hay, or other forages harvested for winter feeding.

Berger and Drewnoski note that grass tetany is sometimes referred to as grass staggers or hypomagnesaemia. Called by any of those names, tetany is a metabolic disorder related to a deficiency of magnesium (Mg). Because magnesium is critical to an animal’s nervous and muscle systems, tetany can present as hyperexcitability, reduced feed intake, and muscle twitching, especially around the face and ears, or cattle may also appear uncoordinated and walk with a stiff gait.

The extension specialists note, “A mineral analysis showing less than 0.15% magnesium in hay is considered low.” When hay and other forages are critically low in one mineral, they often have imbalances, either deficiencies or surpluses, of other important minerals such as calcium and potassium. Because potassium interferes with magnesium absorption, having an excessive amount of potassium in a feed source can induce tetany as well. On the other hand, sodium helps transport magnesium from the food source to the bloodstream within the digestive system, so it is imperative to supply enough sodium for your livestock.

Below are Berger and Drewnoski’s suggestions to prevent winter tetany:

• Test hay for mineral concentrations to identify any imbalances.

• Consider feeding a supplement with high calcium, high magnesium, and salt if hay tests low in magnesium (less than 0.15%) and calcium (less than 0.40%) and high in potassium (more than 2.5%). The supplement should contain 10% to 13% Mg for a 4-ounce target intake.

“Because magnesium oxide is bitter, adding dried distillers grains or soybean meal at the rate of 1 pound to 50 pounds of the mineral and salt mix can help to increase intake if consumption is not at targeted level,” the specialists suggest.

• Deliver supplemental magnesium with a hand-fed protein or energy supplement. Also, provide loose salt with this type of feeding system.

• Examine the concentration of potassium in mineral supplements. If feeds are already high in potassium, feeding additional potassium in a mineral only enhances the problem.

• Feed hay that is higher in calcium and magnesium together with other forages that are high in potassium and low in magnesium. Alfalfa can often be a high-potassium hay.

C.J. Weddle

C.J. Weddle served as the 2020 Hay & Forage Grower editorial intern. She currently attends Mississippi State University, majoring in agricultural education, leadership, and communications. She grew up on a farm in Vardaman, Miss., where her family raises sweet potatoes and soybeans.