| Introduction
Quality
Bioavailability
Profile
AF 2000
AF 600
Process
Dairy Cattle
Beef Cattle
Swine
Broiler
Chickens
Chicken Breeders
Laying Hens
Market Turkeys
Turkey Breeders
Horses
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Sources of
Selenium
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Selenium is found
naturally in some feeds, although concentrations vary greatly by
feedstuff and the region in which the feedstuff originated. Selenium
may be supplemented in either the organic or inorganic form.
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Organic selenium is
composed largely of selenomethionine and selenocysteine, while
inorganic selenium is simply a salt, usually sodium selenite or
sodium selenate. Selenium-enriched yeast is an excellent source of
organic selenium.
Selenium
Status
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The selenium status of
an animal may be assessed by measuring the level of selenium in the
milk, blood plasma or serum, whole blood, as well as blood or liver
glutathione peroxidase activity.
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Selenium and vitamin E
work together as antioxidants, and thus proper supplementation of
both is essential.
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Period required to
affect selenium status depend on ruminal environment and the source
of selenium fed. This period ranges from 7 - 14 days in milk, 30 -
60 days for whole blood and plasma (serum) and 90 - 120 days for
liver selenium and glutathionie peroxidase activity (GSH-Px).
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Blood plasma or serum
selenium content is a good indicator of changes in selenium
supplementation. Whole blood, GSH-Px and liver selenium are better
indicators of longer-term (90 - 120 days) supplementation.
Bioavailability
of Selenium Sources
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Organic selenium is more
bioavailable than inorganic selenium.
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Inorganic selenium is
reduced to un-absorbable elemental or inorganic selenides in the
rumen.
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Rumen bacteria take up
more organic selenium than inorganic selenium, making bacterial
selenomethionine and selenocysteine.
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Limited data suggest
that the true digestibility of selenium from feeds is between 40 and
65% for ruminants. Digestibility and absorption is 8 to 15% higher
with organic selenium.
Economic
Return for Feeding Selenium
At current feeding rates where inorganic selenium is fed
regularly at 6 mg/hd/d, deficiencies still occur. The cost benefit ratio
of supplementing dairy cows with 3 mg/hd/d from selenium yeast was
calculated to be 7:1. This is due to increased bioavailability and
longer retention in the body for selenium yeast at legal limits.
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