A FORAGE FACTS Publication of the KANSAS FORAGE TASK FORCE
Kansas State University Agricultural Experiment Station and Cooperative Extension Service
GRASS TETANY
INTRODUCTION
Grass tetany, also called grass staggers, wheat pasture poisoning, magnesium tetany and hypomagnesia, is
a magnesium deficiency of ruminants usually associated with the grazing of cool-season grasses during spring. It
is most prevalent among older cows in early lactation, but may also affect young or dry cows and growing calves.
Grass tetany occurs most frequently when cattle are grazing lush, immature grass, but occasionally occurs when
cattle are fed dry forages (winter tetany).
CAUSES
Grass tetany is a nutritional or metabolic disorder
characterized by low blood magnesium, yet it is
not just a simple magnesium deficiency. Low blood
magnesium may be caused by (1) a diet low in magnesium,
(2) a diet with nutrient imbalances that interfere
with magnesium metabolism, or (3) high levels of milk
production. When blood magnesium drops too low,
proper nerve impulse transmission fails, causing the
disorder.
Magnesium needs are greater for lactating than
for nonlactating animals and greater for older than for
younger animals. There are differences among bovine
breeds in susceptibility to grass tetany with Brahman
and Brahman crossbreds being more tolerant and European
breeds being less tolerant. Many factors influence
forage magnesium concentration and availability. The
principal factor is a high level of potassium, which
negatively affects soil magnesium uptake by plants and
the availability of the forage magnesium to the animal.
High nitrogen content of grass seems to also be associated
with low blood magnesium. High nitrogen fertilizer
may reduce magnesium availability, especially on
soils high in potassium or aluminum.
Grass tetany occurs most frequently in the
spring, often following a cool period (temperatures between
45 and 60°F) when grass is rapidly growing, but
also is seen in the fall with new growth of cool-season
grass or wheat pasture. It occurs most frequently in
cows that are nursing calves under 2 months of age,
and is more likely to occur in beef herds than in dairy
herds. Grass tetany seldom occurs when legumes and
legume grass mixtures are a major portion of an
animal's diet. Legumes may contain over twice the concentration
of magnesium as do grasses grown on the
same soil.
SYMPTOMS
Quite frequently, clinical signs of grass tetany are
not observed and the only sign is a dead animal. Affected
animals may become excitable-exhibiting a
wild stare with erect ears and appear to be blind. They
are uncoordinated and tend to lean backward and
stumble or go down. The following progressive series
of signs have been observed in cattle affected by grass
tetany: (1) grazing away from the herd, (2) irritability,
(3) muscular twitching in the flank, (4) wide-eyed and
staring, (5) muscular incoordination, (6) staggering,
(7) collapse, (8) thrashing, (9) head thrown back,
(10) coma and (11) death.
PREVENTION
The prevention of grass tetany depends largely
on avoiding conditions that contribute to the disorder.
Some of the management practices to avoid grass
tetany include:
FORAGE FACTS Publication Series
Research and Extension
• Avoid grazing cattle on new grass until it is 4 to 6
inches tall because magnesium is less available in
very immature plants.
• Feed legume hay or graze mixed legume-grass
pastures since legumes are higher in magnesium
than grasses.
• Graze less susceptible animals on high risk pastures.
Heifers, dry cows or cows with calves over 4 months
old, and stocker cattle are less likely to develop
tetany.
• Feed a magnesium supplement.
In areas where tetany frequently occurs, routinely
feed cattle supplemental magnesium which increases
blood magnesium levels and alleviates much of
the grass tetany problem. Magnesium is not stored by
the body, so care must be taken to ensure that each animal
receives the proper amount on a daily basis. Begin
supplementation before cattle are turned out on tetanyprone
pasture, and continue until the threat is minimal.
Magnesium oxide is a good source of magnesium, but
since it is not palatable, it should be included in a
highly palatable energy or mineral supplement. Magnesium
oxide (54 to 60 percent magnesium) can be
added at the rate of 75 to 150 pounds per ton of supplement
when 1 pound per head is fed daily. Alternatively,
a "High Mag" mineral containing 8 to 10 percent magnesium,
should be fed free choice.
Kansas State University Agricultural Experiment Station and Cooperative Extension Service
Issued in furtherance of Cooperative Extension Work, acts of May 8 and June 30, 1914, as amended. Kansas State University, County Extension Councils,
Extension Districts, and U.S. Department of Agriculture cooperating, Richard D. Wootton, Associate Director. All educational programs and materials
available without discrimination on the basis of race, color, religion, national origin, sex, age, or disability.
TREATMENT
Treatment results vary from excellent to poor depending
on the clinical stage of the animal at the time
of treatment. If treatment is started within one to two
hours after clinical signs develop, the results are usually
a quick recovery; however, in a large pasture it
may be difficult to quickly identify sick cattle. Pasture
cattle should be observed at least twice a day when
they are first turned to grass. Treatment of animals that
are in a coma may be too late. The normal treatment is
intravenous injection of a commercial preparation of
magnesium and calcium in a dextrose base. Consult
your veterinarian, and have medication on hand before
turning cattle out to graze.
SUMMARY
Grass tetany is a result of a magnesium deficiency.
Clinical signs usually begin with nervousness
and staggering and progress to falling, coma and
death. Grass tetany is always an emergency requiring
immediate medical attention. Treatment consists of intravenous
administration of a magnesium and calcium
solution. The injection of magnesium sulfate under the
skin may provide a high level of magnesium in the
blood in 15 minutes. The best prevention methods include
keeping cattle off new grass until it is 4 to 6
inches tall and supplementing magnesium on a daily
basis when conditions are favorable for grass tetany.
Contact: Dale Blasi
Extension Specialist
Forage Nutrition and Management
Telephone: 785-532-1249
FAX: 785-532-7059
E-mail: dblasi@oz.oznet.ksu.edu