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Re: Selenium - Vitamin E (Long)

On Wed, 7 Oct 1998 19:34:45 -0700 (PDT), Trish Grant <>

> I know there has been alot on ridecamp regarding selenium, but I have one
> more question here. I am aware that in order to get maximum benefits of
> the selenium it must be complimented by vitamin E. I am feeding my horse a
> supplement that has a good ratio of selenium in it but there is no Vitamin
> E. Can I then add solely a vitamin E supplement to compliment the
> selenium. If this is possible what kind of vitamin E can I feed. Can I
> feed a people type vitamin E or is there something specific for horses. If
> I can feed a people type vitamin E any suggestions on which kind to feed,
> a gel type pill, a regular type pill or some powder substance of such,
> and then if I cannot
> feed a people type vitamin E any suggestions. Does anyone know the ratio
> needed of selenium verses vitamin E to make an effective supplement.


While your endurance horse is working, the energy and oxygen used in
producing work is broken down carbon dioxide and water.  Free-radicals
are also formed while the oxygen is reduced to water, which are harmful
to the body because of their ability to oxidize and destroy the protein
and lipid (fat) components of living cells.  Vitamin E prevents these
free-radicals from attacking lipids by "blocking" their ability to
attack the cells, while selenium (in short) prevents the formation of
free-radicals via the enzyme glutathione perioxidate and destroys lipid
peroxide (which is a result of free-radical attack on lipids). 

So, if this is thought out a bit, you'll find that endurance horses
require more vitamin E and selenium per day than the idle pasture
ornaments next door due to the amount of work they are asked to do. 
More work = more free-radical production.  

The amount of these nutrients needed should be considered as "how much
does my horse need of each" rather than as a ratio of one to the other. 
The vitamin E recommendations for a particular class of horse is based
on IU (international units), which is more of a measure of biological
activity or "strength" rather than quantity, per se.  Selenium on the
other hand is based on ppm (parts per million, or mg per kg).  The
recommendations for both nutrients are on a "mass of dry matter feed
eaten per day" basis, rather than directly on a horse's weight or energy
intake which is usually a basis for many other nutrients.

So, how much does my horse need?  Endurance horses and broodmares
(either in their last trimester, foaling, or lactation) should have a
minimum of 0.2 ppm of selenium per kg of *dry* matter feed per day.  The
maximum safe daily limit is 2 to 5 ppm of selenium per kg of dry matter
feed.  Dry matter feed used in these calculations has no moisture at
all: 100% dry matter. Many properly cured hays tend to have about 91%
dry matter content, and grass forages around 25% or so.  These numbers
can vary wildly.

So, as an example, Lee (my mare) will happily eat 22 pounds of
alfalfa/grass hay per day to maintain her current condition (she's a big
girl ;-)).  This 22 pounds is equivilent to about 10 kg of hay (22
pounds multiplied by a conversion factor of 0.4536).  If we assumed that
the hay was at 91% dry matter and she was an endurance horse or
broodmare, she would require 1.82 mg of selenium per day MINIMUM from
her feed (9.1 kg dry matter feed * 0.2 mg/kg selenium required).  If we
played conservative and wanted to find her upper safe limit, just
multiply 9.1 kg of DM feed with 2.0 mg/kg selenium per day, and her
maximum limit would run about 18.2 mg of selenium per day.

For vitamin E, the endurance horse/broodmare requires a minimum of 100
IU per kg of dry matter feed per day.  There is more "leeway" on the
maximum levels fed each day, but 1000 IU/ kg of DM feed per day is the
maximum recommended (long term) before you start seeing Vitamin E

Vitamin E horse supplements use a synthetic form of alpha-tocopherol
(dl-alpha tocopheryl acetate) which has been esterfied and breaks down
only in the horse's digestive tract --- naturally-occuring forms such as
d-alpha tocopheryl acetate (notice the "l" is missing) are unstable to
use for supplements because of their ease in oxidation.  If you look on
the label of your vitamin E supplement, it should state the "IU per mg"
information for that form (which for dl-alpha tocopheryl acetate, is
about 1.00 IU/mg).  Synthetic forms are less biologically available to
the horse than naturally-occuring forms found in feed, which is why the
biological activity of dl-alpha tocopheryl acetate is a bit low.  

So, if we used Lee as our "lab rat" again:  She eats 10 kg of hay per
day, which is equivilant to 9.1 kg of dry matter feed.  Multiply 9.1
with 100 IU of vitamin E required, and she will need a MINIMUM of 910 IU
of viamin E per day.  Her feed will provide a significant amount or can
meet her needs, but this varies depending of the type of feed and growth
stage when harvested.  If we assume that she is not taking in any
vitamin E *at all* and we are supplementing her with a "pure" vitamin E
product with a biological activity of 1.00 IU/mg, then she would need
910 mg of the supplement per day.  This is where the labels are
important --- how many IU of vitamin E are you really getting per scoop
of supplement?  And, a good hay cut early and cured/stored properly can
provide at least half or more than Lee's vitamin E needs as an endurance
horse.  Even better, good quality, nutritious growing forage can meet or
exceed Lee's needs for vitamin E as well.

Where can you find an inexpensive source of vitamin E?  Well, there's
the Horse Health USA's catalog ( or for the web inabled of us), which has several
vitamin E supplements reasonably priced (thanks Julie of Rayna fame). 
You'll notice that the biological activity is in IU/pound, which needs
to be converted to fit their 1 ounce scoops.  Probably a lot less
expensive than using the "human" supplements.

Hope it helps!

Kim (and Lee)

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