Agricultural News: Protect Your Cattle Herd from Grass Tetany

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   Spring is right around the corner, and I am welcoming it with open arms! I’d imagine our cattle are, too.  After eating hay all winter the lush, green grass is likely a sight for sore eyes. However, that quick, lush growth following a cold, wet winter is full of moisture and potentially diluted minerals, which can lead to a highly fatal disease known as Grass Tetany.

   A couple weeks ago I shared an article about hi-mag minerals by Dr. Katie Mason. I want to take some time to bring grass tetany to your mind again because we are coming out of the ideal winter conditions to see magnesium-deficient grass. 

   Grass Tetany is associated with low levels of magnesium (Mg) in the blood. It can affect all classes of cattle, but older cows with calves on their sides during late winter and early spring are most at risk.   Magnesium is a very important macromineral for cattle, especially for older, lactating females. Cattle store Mg in their bones and muscles, but it is not made readily available to the animal when blood levels of magnesium drop. Cattle constantly lose magnesium in urine, feces and milk, so when grazing lush green magnesium-deficient grass, cattle need magnesium supplements to meet daily requirements. Also, cattle in peak lactation (6-8 weeks post calving), need a constant source of magnesium to replace a large amount lost from the body in milk. 

   Although grass tetany is most commonly associated with grazing cool-season grasses with a low amount of magnesium (Mg), there are several other causes of grass tetany. They include:

•Grasses grown on leached acid sandy soils have lower levels of magnesium

•Low soil temperature which depresses Mg uptake by plants

•High soil moisture which depresses Mg uptake by plants

•Over fertilization with Potassium (K) and Nitrogen, which causes lush growth and also depresses the plant’s ability to uptake Mg, especially after a long, cold winter

•Low intake of phosphorus and salt

•In the rumen, Mg absorption is reduced when there’s too much potassium and nitrogen and not enough sodium 

•Low energy intake, fasting, or sudden dietary changes

•Transport stress

   Unfortunately, most animals suffering from grass tetany are found dead. There may be signs of struggle on the ground. Early signs of grass tetany include: (1) Grazing away from the herd, (2) irritability, (3) flank muscle twitching, (4) wide-eyed, staring, anxious expression, (5) muscular incoordination/stiff gait (6) staggering, (7) collapse, (8) thrashing, (9) head thrown back, (10) coma, and (11) death. Aggression is also often observed in cattle suffering from low blood Magnesium. 

   Cattle suffering from grass tetany usually respond to IV calcium/magnesium solutions. However, in acute cases where timing is critical, you can administer an Epsom salt solution via an enema while waiting for your veterinarian. IV calcium/magnesium is still needed to reverse the effects of grass tetany.  

   So how do we prevent grass tetany? It all boils down to management. Here are some prevention considerations:

•Increase energy and roughage intake.

•Good quality hay or silage is suitable.

•Pellets or grain can be added if introduced carefully.

•Provide a balanced mineral source. Loose is preferred during the high-risk periods to ensure their daily requirements are met. 

•Move lactating cows (especially older animals) to high legume and high dry matter pastures.

•Reduce stress factors.

•Provide magnesium supplements.

•Correct soil acidity with lime or dolomite (dolomite contains some magnesium).

•Plant clovers. 

•Apply phosphate fertilizer.

•Limit potash and nitrogen applications until soil acidity is corrected and clovers are established.

   If you suspect you have a cow suffering from grass tetany, contact your veterinarian right away. If you have any questions about grass tetany, please call or email me at 931-722-3229 or mdharris@utk.edu. 

   Some information in the article has been adapted from UT Publication W 789, Image courtesy of UTIA.