Mitigate Grass Tetany and Improve Herd Mineral Status

Feb 03, 2020

As winter yields to spring, grass begins to “green-up” and pastures become dotted with new baby calves.  Along with calving season cow-calf producers will also manage grass tetany season. In an effort to mitigate loss, the time-tested practice of providing cattle with supplemental magnesium often in the form of “Hi Mag” minerals is often employed.  This is done to help guard against hypomagnesemia (low blood magnesium) or grass tetany.   This serious and often fatal metabolic disorder is referred to the ‘silent killer of spring’.  The disease gets it nickname as grass tetany strikes mostly in spring, though it can occur in fall or early winter.  The truth is that cows are at risk most anytime that grass or small grain pasture is lush and growing. 

Grass tetany is most often associated with conditions of low magnesium and high potassium in growing pastures.  Many factors affect these mineral levels in forages and include soil temperature, moisture, and fertilization program.  Often, cattle operations that strive to do a good job with forage production are plagued with more incidences of grass tetany.  Also, there are certain factors that influence susceptibly in cows.  Grass tetany usually affects mature cows that are heavy in lactation.  This has to do with an increased demand for magnesium and calcium coupled with the reduced ability to mobilize minerals from bone in mature animals.

Fortunately grass tetany is treatable when discovered and diagnosed early, but as with many common disorders, prevention is preferable as it is generally less expensive, more effective and less laborious to prevent versus treat.  Since grass tetany is a disorder involving mineral metabolism, it stands to reason that mineral supplementation would be an efficacious method of prevention.  Complete supplementation with trace minerals and fat-soluble vitamins included in Co-op Hi Mag Cattle minerals has numerous benefits.  Supplemental magnesium is usually the focal point of “Hi Mag” minerals but, given the fact that many cows are in late gestation or heavy lactation during grass tetany season, there are many potential rewards to be realized from complete vitamin-mineral supplementation.

In most of the Southeast, forages are not nutritionally adequate in copper, zinc and selenium.  These trace minerals are of utmost importance for brood cows in late gestation, lactation and during breeding season.  Fall calving cows will usually be in heavy lactation during most of grass tetany season while spring calving cows will often be in the last weeks of gestation and early lactation.  Furthermore, grass tetany season immediately precedes breeding season for many spring calving herds.  These stages of production and the physiological stresses that accompany them emphasize the need for complete mineral and vitamin supplementation in addition to supplemental magnesium. 

Copper plays a role in numerous processes throughout the adult animal and the developing fetus.  Of most importance to cow-calf producers are those processes associated with growth and reproduction.  Cattle that are grazed in areas with excessive sulfur in soil, forages and/or water may be in greater need of supplemental copper as dietary sulfur is an antagonist to copper absorption.  Likewise, zinc is involved in several functions and most are related to health and immunity.  Selenium and vitamin E work in synergy and are involved with reproduction, immune function and with the expulsion of the placenta after calving. 

Recent research suggests that heifers born to mothers that received adequate trace mineral supplementation are more productive throughout their lives than those born to inadequately supplemented dams regardless of their own nutritional program. This is commonly referred to as fetal programming and shows that the benefits of mineral supplemental are realized far beyond the animal that directly ingests the mineral supplement.  In terms of health, growth and increased productivity, vitamin and mineral supplemental provides a very attractive return on investment.  As you strive to guard against grass tetany by providing supplemental magnesium, work with your local Co-op® livestock specialist to tailor a cattle mineral program to help guard against loss and improve your bottom line.

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