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Selenium availability in ruminants
Cattle, sheep and goats in Alberta and other parts of Canada often need extra selenium. Selenium is needed to prevent development of nutritional muscular dystrophy, retained placenta, metritis and other symptoms of selenium deficiency in animals on low selenium diets, which may result from feeding many feeds produced in Western Canada.
On the other hand, over-supplementation is dangerous because selenium is a toxic mineral. Supplements need to provide sufficient but not toxic levels of selenium.
Ruminants absorb only 11 to 55 percent of selenium in feed, considerably less than single-stomach species such as pigs. Apparently, rumen micro-organisms change selenium to insoluble, less available chemical forms.
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Some people believe organic selenium is more available and better than the inorganic form as a supplement. At the Agriculture Canada Lethbridge research centre, scientists used selenium-stable isotopes as tracers to see if inorganic or organic selenium was a superior supplement for sheep. Sheep were fed a diet based on either a forage (alfalfa hay) or concentrate (78 percent barley).
Selenium absorption and retention was higher for sheep receiving the concentrate diet than for those receiving the forage diet. A lower acidity and microbial populations within the rumen of animals fed concentrate diets enhances the availability of selenium. Diet affects the availability of selenium, but it affects inorganic and organic forms equally.
-Agriculture Canada
