Pet Columns, Office of Public Engagement, College of Veterinary Medicine at the University of Illinois at Urbana-Champaign

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Selenium Deficiency in Horses

Pet Column for the week of January 27, 1997

Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
By Joseph Hahn
Information Specialist

Selenium, in conjunction with vitamin E, is necessary for proper functioning of the immune
system and to protect the integrity of cell membranes. However, there is a delicate balance
between too little selenium and too much.

"Because selenium can be toxic if fed in too great a quantity, many people are unwilling to
feed it to their horses," says Dr. R. D. Scoggins, retired equine Extension veterinarian at the
University of Illinois College of Veterinary Medicine at Urbana. "But in the proper
quantities, it is very safe and effective."

Selenium is a mineral found in the soil in many areas of the country. Horses normally ingest
selenium while foraging. In other areas--the Midwest for example--selenium is deficient in
the soil, and without proper supplementation horses can have significant problems.

"Clinically, selenium deficient horses will often 'tie-up,' a degenerative condition of the
muscles also known as rhabdomyolysis," says Dr. Scoggins. "It can affect the heart muscle,
the muscles of respiration, as well as the large muscles of the

back and limbs. It can also cause a decrease in the efficiency of the immune system, leading
to opportunistic infections."

A horse that has rhabdomyolosis will have severe muscle cramps resulting in sweating,
stiffness, and increased pulse. The breakdown of muscle cells can result in coffee-colored
urine. "Do not walk a horse that is tied up," stresses Dr. Scoggins.

While selenium deficiency is not related to the time of year or the horse's sex, it is especially
a problem in growing horses. Detection of selenium deficiency can be done with a simple
blood test that can be run inexpensively at many veterinary diagnostic laboratories.

Dr. Scoggins does not recommend routine testing for selenium deficiency or toxicity unless
it is suspected based on clinical signs.

"Many different sources of selenium are available for supplementation," says Dr. Scoggins.
"The most important factor is selecting a source of the proper strength and selenium content
that is available for digestion. Only one consistent source should be used. A free-choice
salt/mineral mix containing selenium is the safest form of supplementation."

Acute selenium deficiency can be treated with an injectable product, which is commercially
available and quite safe. This medication is used to increase selenium levels immediately,
and oral supplementation is used thereafter.

"The supplementation rate for selenium is generally 1 mg per horse per day," says Dr.
Scoggins. "Supplementation can go as high as 2 to 3 mg per day without any ill effects.
Doses of 5 mg per day can lead to problems with selenium toxicity."

Dr. Scoggins emphasizes that there is no one proper supplementation method. It is
important to discuss this problem with your local equine veterinarian to determine the soil
availability of selenium in your area and to decide what methods are right for you and your