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Managing Grass Tetany

February 11, 2019

By Chelsey Saevre, M.S. & Mike Jarosz, Ph.D.

Tetany Characteristics

As we transition into warmer weather, discussions involving grass tetany begin to rise. Often times, cattlemen focus on magnesium deficiency as the main culprit for tetany.  An understanding of all nutrient interactions involved in the onset of tetany is important when developing a prevention strategy.  Forage type, cattle condition, and climate can contribute to the onset of this metabolic concern in the cowherd.

Tetany is a neurological syndrome with a quick onset where cattle may express signs of excessive alertness, nervousness, and reduced feed intake.  As tetany progresses, cattle may convey a staggered, uncoordinated walk, salivate profusely and drop with convulsive spasms.  Death can occur as quickly as 2 or 3 hours after the initial onset of symptoms. (Hume, 2009).

Tetany can occur in all classes of cattle, specifically when they do not consume a sufficient amount of available magnesium.  Cows in late gestation or early lactation are more prone to tetany as these cattle require increased levels of magnesium and calcium.  Older, lactating cows are at greatest risk due to their reduced ability to mobilize body reserves of magnesium.  Magnesium absorption can also be reduced by high levels of dietary potassium, low sodium levels, reduction in rumen fermentation, as well as low calcium and phosphorus levels (Church, 1988).

Grass Tetany

During the spring months, grass tetany commonly occurs when beef cows consume lush, rapidly growing grasses.  These grasses typically contain low magnesium, low calcium, and high levels of potassium.  Forages containing high potassium (K) worsens the tetany potential of already low magnesium (Mg) forages whereas the concentration of potassium increases in a forage it decreases the absorption of magnesium (Figure 1). As a general rule of thumb, cattle consuming lush forages containing less than 0.2% magnesium, greater than 3% potassium, and/or are greater than 25% protein (DM basis) may result in grass tetany (Allison, 2003).  Grass tetany has occurred with cattle consuming the following forages; orchard grass, perennial ryegrass, timothy, tall fescue, crested wheatgrass, bromegrass, cheatgrass, and while grazing small grain forages such as wheat, oats, barley, and rye (Allison, 2003).

Tetany Prevention

During conditions when tetany may be prevalent, it is important for cattlemen to consider preventative management strategies to avoid tetany.

  • Analyze basal forages to ensure forages contain adequate and balanced mineral levels to meet cattle requirements.
  • Consider feeding legume forages such as alfalfa to provide supplemental magnesium and calcium.
  • Provide supplemental hay or grain concentrates when cattle are grazing tetany prone forages.
  • Provide supplemental magnesium. Data would suggest providing approximately 17 grams of supplemental magnesium per head per day may help protect cattle from grass tetany (Gill, et al., 2002).

Magnesium Supplementation

Supplementation with elevated levels of magnesium can be an effective way of meeting dietary magnesium needs.  Supplements containing high magnesium may be unpalatable to cattle.  It is important to monitor consumption to ensure cattle are meeting their dietary needs.

QLF liquid supplements and Ignite tubs are an effective way to supplement magnesium to the diet. Contact your local QLF representative for more information.

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