In the News - January 2008
Warning: Grass tetany can be late winter problem
FAYETTEVILLE, Ark. - Arkansas beef and dairy cattle producers need to be wary
of a potential late winter problem disease - grass tetany. This disease is also
called winter tetany, wheat pasture poisoning, lactation tetany and magnesium
deficiency.
"Once cool season forages begin to re-emerge in your grazing pastures, grass tetany can become a potential problem," said Dr. Jeremy Powell, assistant
professor/veterinarian for the University of Arkansas Cooperative Extension
Service. "This disease, which normally occurs in February, March and April, is
caused by an abnormally low level of magnesium in the cow's body."
Ruminant animals absorb magnesium from the intestinal tract much less
efficiently than other species, he explained. Magnesium deficiency can occur
from losses in the milk of a lactating cow or because of an increase in the
cow's potassium intake.
Powell said high potassium levels interfere with a cow's ability to absorb
magnesium from the intestine.
"High potassium levels occur in young, rapidly growing forage and can be a
problem in cool season grasses such as fescue or in winter annual cereal grains
such as wheat and oats," Powell said.
Spring fertilizer applications can further increase high potassium levels in
the forage. Heavy fertilization of grazing pastures with potassium (potash), can
eventually further hold back magnesium absorption in a cow's gastrointestinal
system.
"All of these factors are likely occurring about the same time in the cow's
environment during the late winter and early spring," Powell said.
Grass tetany typically occurs in mature, lactating cows. It more commonly
affects cows that are slightly over-conditioned and would likely be referred to
the "best" cows in the herd. However, it can also affect excessively thin cows
with a poor body condition.
Younger herd animals rarely have problems with this disease.
"Weather can play a role in grass tetany," Powell said. "It's usually cloudy,
misty, and/or cold when this disease occurs. These weather conditions decrease
the plant's ability to use magnesium, causing it to be even less available for
grazing animals. Other stressors on the cattle such as hauling, penning, or
transport can also promote the disease."
Early on, cattle affected by grass tetany may show subtle signs of illness
such as decreased appetite, decreased milk production, frequent urination,
separation from the herd, increased excitability as well as a stiff or unsteady
gait, according to Powell. These early signs may occur for as little as two or
three hours, making early detection difficult. As the disease progresses, an
affected cow will lose normal muscle control. This forces the animal to lie
down, and she may be unable to get up. Affected animals will usually exhibit
muscle tremors and spasms. Other signs can include a profuse salivation,
over-excitability, increased pulse and respiratory rates and eventually death if
untreated.
"If your cattle aren't checked often, a dead cow can commonly be the first
sign of a problem," Powell said.
The disease can be prevented by a salt-mineral supplement containing at least
10 percent magnesium. It must be made available on a daily basis.
Several mineral feeders should be made available if stocking rates are higher
for the herd. Mineral feeders should be conveniently located in the pasture so
that cattle have adequate access to them.
Producers may need to review fertilization practices to make this disease
less prevalent. Fertilization should be based on recent soil samples taken from
the pasture.
Since the disease rarely occurs in young animals, high risk pastures can be
grazed by stocker calves instead of mature cows as another method of controlling
this disease, Powell recommended.
For more information about cattle diseases, contact your county extension
office. The Cooperative Extension Service is part of the U of A Division of
Agriculture.
January 18, 2008
Media Contact: Lamar James
Extension Communications Specialist
U of A Division of Agriculture
Cooperative Extension Service
(501) 671-2187 or (501) 753-0207
ljames@uaex.edu
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