Feeding Facts: Grass Tetany

BY JIMMY PARKER

There have been thousands of articles written about grass tetany, but since it is the most common time of year for this particular problem, it seems prudent to do yet another one, especially since there are some relatively new twists in the research on ways to prevent the disorder.

Grass tetany is a most often fatal nutritional or metabolic disorder characterized by low blood magnesium levels. It is not as simple as just a magnesium deficiency and several factors can play a role. Some of those factors include low dietary magnesium, low salt intake, nutrient imbalances such as high nitrates or potassium, ambient temperature, frost or freezes, types of forages and fertilization practices just to name a few.

Magnesium levels in the blood are important for many reasons and when it gets below a required threshold, animals tend to lose coordination, collapse and die within a short time. There are effective treatments if caught early on, but generally the first noticeable sign will be a dead animal. Prevention is the best strategy available.

We normally see grass tetany on cool, cloudy, early spring days. Most often these days follow a warm spell which was followed by a freeze or frost and cattle are grazing young, tender, frost-damaged grasses that have been fertilized. Offering high quality hay or dry lotting cattle on such days can help in prevention, but may not always be possible.

When cattle graze frost-damaged young grass, there is typically a spike in nitrate levels in the blood. Cattle generally use sodium to tie up and eliminate the excess nitrates, but when sodium levels are not sufficient, the next best option is magnesium. This, along with high levels of milk production, will cause severe magnesium deficiency in the blood stream and grass tetany becomes likely.

Grass tetany is most often seen in middle-aged to older cows that are nursing young, less than 60-dayold, calves. Peak milk production is one of the important contributing factors. Another set of factors is the type and maturity of the forages being grazed combined with the fertilization practices. Cool-season grasses, both perennial grasses such as fescue and winter annuals such as ryegrass and wheat, are among the riskiest. Adding a legume, such as clover, will significantly reduce the occurrence of grass tetany because legumes tend to bring more magnesium from the soil when compared to cool-season grasses.

The most common and surest prevention is to make sure that cattle are consuming a high magnesium mineral such as the Formax Grazing minerals during times of highest risk. It is recommended to switch to higher magnesium mineral a few weeks before the grass begins to grow rapidly and keep your herd on those minerals well after the greatest risk has passed. With that said, magnesium supplements tend to be bitter and are not palatable and extreme care is needed to make sure that the cattle are consuming the needed amount every day. Cattle do store limited amounts of magnesium in bone, but do not store it in the blood stream. They cannot metabolize the bone magnesium rapidly enough to be useful when blood nitrate levels spike during that perfect storm that causes grass tetany.

This reduction in salt cravings can reduce salt and mineral consumption and adds to the chances of seeing grass tetany by reducing both the sodium and magnesium available to the animals.

To summarize the best ways to avoid grass tetany in your herd, a good place to start is providing a high magnesium mineral supplement such as the Formax Grazing minerals. When possible, waiting to graze grasses until they are taller than six inches and grazing younger animals and those not lactating on the higher-risk pastures makes sense. Fertilizer is good and clearly needed, but being aware of how it can contribute to grass tetany is important, as is making sure soil phosphorus levels are adequate. Providing a good quality hay on those days when the conditions favor grass tetany can help prevent problems.

Several environmental, production and nutritional factors must come together to have grass tetany. They all have to line up in the right order at the right time and any one of the management practices listed above will go a long way in preventing the problem. Any two of those management practices will almost rule it out entirely. That is the good news. The bad news is that the factors that we cannot control, like the weather conditions required, often catch some producers by surprise and animals are lost.

Adding a legume, such as clover, will significantly reduce the occurrence of grass tetany because legumes tend to bring more magnesium from the soil when compared to cool season grasses.