Grass tetany in news again

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By Rick Greenwell

In the last month we have shared two pieces of information to cattle farmers about grass tetany. It came up again last week in a very unusual way. There was an article in the April issue of Cow Country News on page 88 titled “Cows Need Salt to Avoid Grass Tetany.”  

This article has caused a significant conversation across the state between producers, vets, specialist and other beef leaders. Here is Jeff Lehmkuhler, University of Kentucky Beef Cattle Nutrition Specialist response in detailed to that article.  

There is a lot of science to it, but it just proves that there is a reason behind magnesium recommendations. Cattle are too expensive right now to lose if we are not using a grass tetany mineral.

Jeff Lehmkuhler’s response to the Cow Country News article is below to help you more clearly understand this issue.

1. Magnesium absorption in cattle primarily occurs in the rumen/reticulum, though there is limited absorption further down the gastrointestinal tract (GIT) in younger animals, the small intestine is a region in which Mg is secreted back into the digestion.

2. Magnesium absorption in the fore stomach is an active process using a sodium-dependent mechanism. This essentially means that energy and Sodium are required to absorb Mg from the rumen fluid into the cells lining the stomach.

Because most active sodium pumps are dependent on potassium as well (sodium goes one way, potassium the other to keep the electrolyte balance within cells correct), the situation becomes a sodium/potassium/magnesium issue. We discuss the interactions among minerals in passing during classes like Master Cattleman and skip the details, but there is SCIENCE behind these mechanisms that IS known.

3. As stated in point 1 above, Mg is absorbed and then excreted; it is the magnesium balance that is important. When cows begin to lactate, additional Mg is lost in the milk, thus the need to absorb more to be later excreted is important.

If the Mg consumed is the limiting factor, then the balance slips and becomes negative, resulting in lowered Mg levels in the blood, which can be detected by sampling, but often is not done. Only when the levels become so low that nerve signal transduction is impaired and tetany is observed are corrective measures applied. PREVENTION is key.

4. Magnesium and calcium are both essential for proper nerve signal transduction. This is why we can see similar symptoms (tetany/muscle spasms). However, this is not to say that a milk fever case, which is calcium-related, can be overcome with magnesium supplementation and vice versa.

5. Excess leads to imbalance – Preach Balance. Because of the routes of absorption, similar charges (Na+, Ka+, Ca++, Mg++), and interactions, excessive consumption of one can impair the absorption of another. These antagonisms are generally highlighted with the trace minerals, but are present with the macro minerals as well.

Forages in the spring can be very high in potassium, low in sodium and magnesium and give rise to grass tetany. To overcome this we recommend a product that has elevated Magnesium mixed with salt and other minerals to provide levels that can overcome the excessive potassium and hopefully ensure adequate Mg uptake. Sodium alone in the form of salt won’t fix the issue if Magnesium intake is low.

6. Why the discussion of salt then?  Most of our forages generally only provide about 60% of the sodium needs. During the spring this is even less. To ensure a proper electrolyte balance, salt supplementation is recommended.

Research has shown that elevated K levels in the diet negatively impacts the absorption of Mg. The ratio of Na:K is important in the active Mg absorption process, thus supplementing with more Na may aid in Mg absorption by maintaining a more favorable Na:K balance.
However, research has shown that salt alone does not provide the same level of production as a complete mineral. Nor will it provide the selenium, copper, zinc or other trace minerals needed.

7. Recommendations – Use a COMPLETE mineral product with elevated Magnesium (12-15 percent) from magnesium oxide (not dolomitic lime) that has a suggested intake on the tag of 4 ounces per day.

Monitor intake to ensure the intake is near 4 ounces, if not, switch to a more palatable product. Magnesium oxide is VERY bitter and cheap products don’t always promote good intakes. PREACH the balance concept.

As the nutritional needs of the class of animal change, we strive to provide a diet that balances the supply requirements.