Selenium

Gerald Hauer, DVM
Bison Production Specialist
Alberta Agriculture, Food and Rural Development
Bison Centre of Excellence, Leduc, Alberta.
Phone: (780) 986-4100

Reprinted from The Tracker, volume 3, issue 6, June 1999

Summary

Selenium is a mineral that is required by the body in small amounts in order to function properly.  Many areas of North America have soils that are deficient in the mineral and therefore livestock raised in these areas are prone to deficiency as well.  Understanding the syndrome associated with selenium deficiency and knowing how to supplement your animals is an important part of modern day livestock farming.

Selenium

Selenium is an important nutrient for the maintenance of normal cells and tissues in the body and is required for good health and production.  Soils in much of Alberta and Western Canada have low to marginal levels of the mineral and this can lead to deficiencies in livestock.  When feeding your bison, elk, and deer you should consider selenium supplementation as a means to ensure adequate intake.

Selenium is a trace mineral that is required by livestock at low levels (about 1.0-3.0 mg/head/day).  Deficiencies of this mineral may cause a variety of conditions such as reduced growth rates, poor fertility, increased susceptibility to infectious diseases, and white muscle disease.  Because a deficiency can manifest itself in a number of ways some people have lumped all of these conditions under one term called “selenium responsive disease”.

If you are concerned about the selenium status of your herd there are some blood tests that can be done to assess their status.  Serum or whole blood selenium levels can tell you if your herd is low, marginal, or adequate.  It is important that several animals (about 10% of your herd) be tested to get an impression of the herd status because testing one or two individuals may give misleading results.  If you are concerned, it is best to discuss testing with your veterinarian.

If it is determined that your herd is low or marginal in selenium or if you farm in an area that the soil is known to be deficient, there are a few ways that you can supplement your herd.  Injectable forms of the mineral exist, but for elk and bison this is not practical. Selenium can also be provided in a free choice mineral or salt mix but consumption is unpredictable.  Some animals may consume adequate amounts while others in the same herd may not.  Feeding grain that has selenium mixed in is the most reliable means of supplementation.  I recommend that selenium be mixed with the free choice minerals while the animals are on pasture and then at strategic times, the selenium should be removed from the free choice mineral and fed with some grain to ensure that all the animals receive it.  The times of the year that are most important are a few weeks before calving and before breeding (be sure that you don’t oversupplement with grain before calving and make your cows too fat)!  Young animals can be supplemented in their grain on a continual basis.

Because there is a small margin of safety with selenium (the toxic dose is not very much higher than the requirement), you should use caution when supplementing.  As a precaution you should only supplement with one source of selenium at any given time.  For example if selenium is being fed in grain and the animals have access to it in the salt, overdosing may occur.  Signs of toxicity include incoordination, diarrhea, blindness, poor hair and hoof growth, and eventually death.  It is a good idea to get some advice from a veterinarian or nutritionist on the best ways to supplement your herd.

One final word about selenium is that it  has a close relationship in the body with vitamin E.  In the body, these two nutrients work together in the prevention of tissue damage caused by naturally occurring, harmful molecules.  Deficiencies in vitamin E can look the same as selenium deficiencies.  Although green grass, grain, and good quality hay have usually have sufficient levels of vitamin E, many supplements have both nutrients mixed together as an extra safety measure.