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November 20, 2024 - Winter Cow Syndrome

Ration balancing is an important tool in maintaining herd health.

Winter tetany has a list of different nicknames including grass tetany, winter cow syndrome, or hypomagnesimic tetany. Nonetheless, winter tetany is a metabolic condition caused by below average blood magnesium (Mg) levels. It can arise when feed is low or borderline in calcium (Ca) and Mg, or when good quality feed is high in potassium (K).

Excess K can interfere with the Ca, Mg, phosphorous (P) balance, hindering the absorption of Mg. The provision of sodium is also important as it plays a role in transporting Mg to the cells.

While the disease can occur at any time of year, grass tetany usually happens as a consequence of turning livestock into immature spring grass or lush cereal forages, while winter tetany is more often the result of cattle consuming poor quality feed, such as hay or straw. The name “winter tetany” is coined as a result of poor-quality grasses used to feed in the winter when paddocks are snow covered and inaccessible. 

Mature animals are far more susceptible to tetany than younger ones due to their inability to mobilize Mg from their bones and are at greatest risk during lactation. Cows with young calves (under four weeks) are more prone to tetany than those with older calves, along with dry cows, heifers or steers.

The first sign of a problem is often the discovery of a dead cow. Sometimes confused with milk fever or acute hypocalcemia (lack of Ca), the signs that a cow may be suffering from winter tetany are reduced feed intake, nervousness, incoordination, staggering and trembling followed by an inability to get up, paddling, excessive salivation and grinding of the teeth.

The time between the appearance of the initial symptoms and death may be as short as four to eight hours, so treatment should begin as soon as possible. As serious as the symptoms may seem, the problem can be turned around rather quickly with intravenous injections of Ca/Mg gluconate. An immediate call to the veterinarian is of paramount importance.

If intravenous injections are not immediately available, then the quick application of some form of Mg, whether by subcutaneous injection, through drenching or by enema with magnesium sulfate, is recommended. While IV treatment is always an option, it is only to buy time until something more permanent can be introduced. With IV treatment blood levels rise rapidly but tend to fall back to previous levels within three to six hours, so additional measures need to be taken to ensure continued recovery.

To prevent winter tetany, nothing beats a feed sample test. The cost is nominal, but the information is invaluable. Mineral content is indicated in the test results so that rations can be adjusted accordingly.

With the feed analysis available, a tetany ratio can be calculated to determine if a particular feed is tetany prone. Simply divide the percentage of K by the sum of Ca plus Mg. If the ratio is higher than 2.2, then the feed is likely to be tetany prone.  

To increase the Mg content in your feed – the addition of alfalfa or other legume hay, which tends to be higher in Mg, will help to adjust the ratio. Producers can also look to add a mineral supplement into their feed to avoid winter tetany. 

Mineral supplements should be thoroughly examined to determine their formulation. If the supplement is high in potassium, then adjustments should be made to balance the formulation and offset the discrepancy.

Clearwater County Agricultural Services is always here to support producers and their herds. For support regarding weathering against winter tetany, give us a call 403-846-4040.