Ag Notes: Lush forage can cause grass tetany in spring calving cows

January 20, 2004|JERRY LITTLE

Grass tetany is a disorder caused by an abnormally low amount of magnesium in the animal's blood. Beef cattle producers in Kentucky have generally been successful in reducing the incidence of tetany. However, the potential still exists for this disorder to be a problem.

Grass tetany occurs most often in cows grazing lush spring forages, especially small grains and cool-season perennials, such as fescue. It is most common in spring calving cows, especially if they are high producers in their third to fifth lactation.

Several factors contribute to the increased incidence of tetany at this time. The magnesium requirement of cows doubles from late gestation to early lactation (from 9 grams to 21 to 22 grams).

When this rapid change in magnesium needed by the cow is coupled with lowered magnesium in the plant along with certain components that lower the availability of magnesium (such as high applications of nitrogen and potassium fertilizers), tetany can develop.


Weather also can have an effect; the greatest threat is when temperatures are between 40 F and 60 F. Temperatures in excess of 60 F for a week markedly decrease the incidence of tetany. When all of these factors are combined, the risk can be high.

Producers should be concerned with preventing tetany. About 2 ounces of magnesium oxide (22 grams of magnesium) is recommended to meet the magnesium needs of lactating beef cows. Since legumes are higher in magnesium than grasses, feeding cows legume hay during the early spring may supply some magnesium.

Cows grazing spring grass pasture should have magnesium in the mineral mixture, starting as early as mid-January.

Many commercial mixtures are available in various forms to prevent tetany. Before you make a purchase, determine if the product will give adequate magnesium intake. This depends on the magnesium content and the expected consumption of the product. Both should be listed on the tag.

If it appears that magnesium intake will not be adequate, a product with more magnesium or greater intake should be used.


An out-of-towner drove his car into a ditch in a desolated area.

Luckily, a local farmer came to help with his big strong horse named Buddy. He hitched Buddy up to the car and yelled, "Pull, Nellie, pull!" Buddy didn't move.

Then the farmer hollered, "Pull, Buster, pull!" Buddy didn't respond.

Once more the farmer commanded, "Pull, Coco, pull!" Nothing.

Then the farmer nonchalantly said, "Pull, Buddy, pull!" And the horse easily dragged the car out of the ditch.

The motorist was most appreciative and very curious. He asked the farmer why he called his horse by the wrong name three times.

The farmer said, "Oh, Buddy is blind and if he thought he was the only one pulling, he wouldn't even try!"

Jerry Little is Boyle County extension agent for agriculture and natural resources.

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