Grass tetany-beat it don’t treat it
By Dr. Jim White

This fall, maintain blood magnesium in your herd

All ruminants are susceptible to a disease characterized by low blood magnesium. You will hear the condition called grass tetany, grass staggers, lactation tetany, wheat pasture poisoning and winter tetany. And the most likely candidates to suffer from it are beef cows grazing rapidly growing cool-season grasses like fescue, brome and orchardgrass. Cows are especially susceptible when they’re still supporting calves.

Magnesium is very important to the central nervous system. Initial tetany symptoms are usually characterized by excessive alertness, wary appearance and a fine twitch of face and ear muscles. The affected animal will be uncoordinated and walk with a stiff gait. After a few minutes to several hours, the animal may suddenly drop with convulsive spasms, lying on its side with rapid paddling movements of the limbs.

Convulsions and death may occur or the animal may become comatose before dying. It is not uncommon for all symptoms to occur in a span of 2 to 3 hours. Often, the producer does not notice any problems until the cow is dead. Usually blood levels of magnesium are about a third that of normal values.

The best approach is to prevent grass tetany. Prevention is much easier than treatment.
Grass tetany seems to prey on British-Continental lactating animals that are consuming lush cool-season grasses. Magnesium absorption declines with age, and Braham-Zebu cattle may either have better magnesium absorption, or their resistance to tetany may be correlated with their lower milk production.

Tetany is seasonal and often occurs 5 to 10 days after the onset of cold, wet weather. At this time, forage is typically low in magnesium, sodium and soluble carbohydrates, but high in nitrogen and potassium.

Aggressive pasture fertility programs can increase incidence of grass tetany, but in defense fall fertility programs, the increased grass productivity more than pays for the cost of feed ingmagnesium supplements.

Avoiding grass tetany
The objective is to maintain adequate magnesium status of the animal. A dry cow has a magnesium requirement of about 10 to 12 grams per day. A lactating cow has a double that requirement—22 to 25 grams a day. Adequate magnesium needs to be available on a regular basis. And remember, the amount of magnesium that an animal can mobilize is limited. It also decreases as the animal ages. After you start feeding, it takes 2 to 3 days before the animal’s magnesium status responds, so get the magnesium products out early. Likewise, the animal’s magnesium status will fall when the supplementation stops, so don't pull the mineral too early.

Adding sodium to magnesium supplementation improves magnesium status. Free-choice minerals with magnesium concentrations over 10 percent are usually consumed by cattle at levels too low to get adequate magnesium into the cow. Cutting the magnesium concentration in half with grain will usually double consumption. Or, you can increase magnesium uptake by providing soluble carbohydrates along with the sodium and magnesium. The increased fermentation of the soluble carbohydrates improves magnesium absorption.

If you really need to get ahead of grass tetany, offer MFA Salt Mix with magnesium. This is a very good strategy in advance of turning cows out on tetany-prone pastures, but make sure to start several days before you let the cows on the pasture.

The gold standard in feeding magnesium is to get 2 ounces of magnesium oxide into each animal every day. Two ounces should prevent grass tetany. When you feed either a bunk ration or a TMR, getting 2 ounces of magnesium oxide into the animals is relatively easy. The problem comes when the high magnesium mineral is offered free choice.

Which product to use
If your herd traditionally has few tetany problems when you supplement feed, and if you want to put something out to cover your bases, try MFA MAGADE. On pastures that are calcium short, try MFA Hi-Mag mineral.

If you’ve seen tetany on your place or have reason to believe you will, you need to get about 20 grams of magnesium into the cows. If you do not supplement feed, but want to put out a free-choice mineral, MFA XI MAG Mineral is a good choice. If you feed a supplement, 3 to 5 pounds of MFA 20% Super Cattle Cubes per day will preclude tetany. Offering salt mix with magnesium will ensure intake.

The losses from grass tetany can be substantial; the cost of prevention is modest. So take a look at your fall and winter grazing plan. And pay attention next spring. When it comes to tetany—beat it, don’t treat it.

How mineral works
Magnesium in transported across the ruminal mucosa by an active sodium-linked process. Sodium deficiency decreases the sodium-to-potassium ratio in rumen fluid, which results in depressed magnesium absorption. This is consistent with field obervations indicating that producers feeding a MFA magnesium product such as XI Mag Mineral, Magnesium Tubs, Ultralyx 20% or Hi-Mag Mineral have far less incidence of grass tetany thatn those offering a straight magnesium supplement such as magnesium oxide. The explanations for the better results when cattle are offered mineral products are:

• The MFA minerals contain both salt and magnesium.
• The MFA minerals have higher intake than does free choice magnesium oxide.
• The MFA minerals also supply phosphorus, which may be an issue on animals just coming off of stockpiled pastures.

The imbalance between protein and carbohydrate in the rumen may lead to a deficiency of absorbable energy from the rumen. If volatile fatty acids and carbon dioxide production are depressed due to a lack of carbohydrate, blood flow to the rumen wall may be decreased resulting in low magnesium absorption.

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