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Simple rules to follow to prevent grass tetany in cows
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Each growing season has a base and peak. And late winter and early spring is usually the peak period for grass tetany occurring in beef cows.

Grass tetany is a disease of cattle and especially milk cows caused in part by inadequate levels of magnesium, which is needed in relatively large amounts. When levels are low, muscular function becomes impaired causing cows to stagger. Their muscles then twitch and are followed by convulsions, which can lead to possible death.

The chance of grass tetany is highest under warm, rainy conditions in early spring and is common when cool weather is followed by a warm period.

The condition can be controlled by adding magnesium oxide to the mineral mix. About 25 grams of magnesium daily should provide protection against grass tetany. About half of the daily intake will come from the feed and half from the magnesium containing mineral mix.

High-mag minerals are necessary only during high-risk situations. The following is a good basic magnesium-based mineral mix which can be used on the farm:

* 30 percent trace mineralized salt

* 30 percent dicalcium or defluroinated phosphate

* 30 percent magnesium oxide

* 10 percent cottonseed meal or soybean meal

A mature cow needs to consume 2-4 ounces (60-120 grams) of the mineral mix daily. Using this level of intake, a mature cow will receive 0.6 to 1.2 ounces (18-36 grams) of magnesium oxide daily. Magnesium oxide is about 60 percent magnesium so the cow is receiving 0.4 to 0.7 ounces (11-22 grams) of magnesium daily from the mix. In most situations this should control grass tetany.

When you use this mineral mix, remove all other salt from the cattle’s diet, because the cattle are consuming the mix for the available salt.

Commercial mixes are also effective in preventing grass tetany. Commonly called high-mag salt blocks, these minerals should contain 11 percent to 13 percent magnesium. For small-sized operations, it may be more practical to purchase a high-mag mineral than to mix individual ingredients. Cattle should consume roughly 1 to 1.5 pounds per week of the commercially available high-mag mineral blocks.

Monitoring consumption of any magnesium supplement is important to ensure cattle are consuming the supplements at a level to provide protection. Magnesium is an unpalatable mineral. Salt and the oil meals are added to increase consumption. Occasionally, higher than 10 percent meal is required to get cattle to consume the needed 2-4 ounces of mix.

Other than palatability, low mineral consumption can be caused by poor mineral feeder placement or an inadequate number of mineral feeders for the number of cows. Locate these feeders in high traffic or loafing areas and provide one feeder per twenty cows. This should enable cows at the bottom of the herd pecking order to consume enough mineral as well.

Forages most likely to produce tetany are winter annuals and fescue. Fertilizing this time of year increases the problem. Offer the high-mag mineral when these conditions exist. However, there is no advantage in using high-mag minerals during the rest of the year.

Michael Wheeler is county extension coordinator for the UGA Cooperative Extension office in Hall County. You can contact him at 770-535-8293, His column appears weekly and on