Winter Tetany - Frequently Asked Questions

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 What is Winter Tetany?
Winter tetany is a metabolic condition caused by lower than average blood magnesium (Mg) levels. This condition occurs when cattle consume poor quality hay or straw, that contain low levels of magnesium, or good quality cereal greenfeed or silage with high levels of potassium (K). High levels of potassium in the diet reduces the absorption of magnesium and calcium (Ca). Cattle depend upon a continual daily supply of magnesium and calcium from the digestive tract to maintain normal blood concentrations. Often in Alberta winter tetany is associated with feeding grain and straw or greenfeed based rations that contain low or borderline calcium and magnesium, and high potassium levels compared to the cow's requirements.

What are the signs of Winter Tetany?
Winter tetany is most commonly found in cows in late pregnancy and after calving. “Downer cows”, as often referred to by producers, is a sign that the cow may be suffering from winter tetany. Affected cows will behave similar to those with milk fever, they are unable to get up. Those cows that have not gone down, often appear uncoordinated, trembling or stagger. Another sign is a dead cow with struggling marks (paddling) on the ground around her head and legs from trying to get up.

How do you treat Winter Tetany?
Active treatment for winter tetany includes intravenous or subcutaneous administration of solutions containing magnesium and/or calcium salts. If your cattle show any sign of the above symptoms producers should contact their veterinarian immediately.

What can you do to help prevent Winter Tetany?
The K/(Ca + Mg) ratio should be less than 2.2 in the feed ration to prevent winter tetany. Have your feed tested and then based upon the results of the available levels of nutrients and minerals appropriate supplementation can be prepared. Work with a nutritionist to achieve an appropriate feeding program. Supplementation of magnesium oxide and limestone are important in ensuring that the cows are receiving adequate levels of calcium and magnesium.

Magnesium oxide is very unpalatable and will need to be mixed with grains or other feeds to hide the taste. Mixing magnesium oxide with either silage, in the salt mineral mix or in the grain are some options.

Approximately 40 grams of magnesium oxide and 80 grams of limestone may be required per cow per day depending on feed test results. If potassium levels are high greater amounts will be required.

Drought Options: Tetany Problems in Beef Cows
Using Straw in Cattle Rations - FAQ

Prepared by Nanita Blomquist, Ag-Info Centre, Alberta Agriculture and Rural Development

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For more information about the content of this document, contact Barry Yaremcio.
This document is maintained by Lorraine McAllister.
This information published to the web on December 5, 2003.
Last Reviewed/Revised on April 24, 2008.