Pasture rebound could bring tetnay

Written by Dr. Jim White, MFA ruminant nutritionist on .

As far as moisture deficits go, we’re still in drought here in the Midwest, but with recent rains we’re seeing rapid growth of cool-season grass that was held dormant earlier in the year due to moisture stress. Much of this forage will be prone to tetany.

There are several factors that increase the likelihood of grass tetany:

1) There is low magnesium and/or high potassium content in rapidly growing grasses and pastures, especially with fall growth of cool season grasses following a drought. If the concentration of potassium is 2.2 times greater than the sum of calcium and magnesium, the forage is tetnay conducive K/(Ca+Mg)> 2.2.

2) High levels soluble crude protein content in lush growth increases chances tetnay.

3) Weather stress both for plants and animals can change plant metabolism and cause cattle to be off feed

4) Lactation: milk is a significant magnesium and calcium sink

5) Nitrogen applied for fall growth and good growing are conducive to the rapid growth that brings tetnay.

6) Lack of supplements offered to cattle (particularly magnesium, calcium, salt, fermentable carbohydrates) put cattle at higher risk.  

And usually, you will run into combinations of the above.

We know that magnesium is a dietary requirement for all cattle. Growing beef cattle have a magnesium requirement of about 0.1 percent of dry matter. For lactating beef cows, that requirement is doubled. Triple it for wet dairy cows.


For nursing cows, the requirement for calcium increases—so do the requirements for magnesium. Logically, nursing cows are at increased risk of grass tetany. It makes sense, too, that heavy-milking cows are at greater risk of grass tetany.

Experiencing stress or fasting will decrease both calcium and magnesium in cattle. Drought conditions, shortage of hay and poor-quality hay might have contributed to such deficiencies in the Midwest herd. Storms, trucking, running the self-feeder empty, or other stressors that cause cattle to stop eating also can precipitate grass tetany.

MFA Salt Mix with magnesium is generally the fastest and most certain method of addressing grass tetany. If modest protein and energy supplementation are needed where labor is an issue, 20% tubs with magnesium are a good choice. If the forage base is protein- and energy-adequate, High Mag Mineral or Mag-Ade meal would be options.

If the producer is hand feeding cubes or a supplement at recommended rates, the likelihood of tetany is extremely remote. Lactating cattle should consume 15 to 25 grams of magnesium per day. If the feed is on offer at all times (such as a free-choice mineral), make sure the feeder doesn’t go empty. Magnesium is not stored well in the body, so frequent consumption is needed.g




(photo by Binaryape via CC, somerights reserved)


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