Re: Vitamin E and Selenium

[Kim <mathew@redhorsetech.com>]

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.  The
additional 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 recommended to be 2 to 5 ppm of selenium per
kg of dry matter feed.  3.3 mg/kg of dry matter feed per day was
considered as a minimum lethal amount for horses in chronic cases,
unless outdated by more recent peer-reviewed research which has found
otherwise. 

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/burmudagrass hay per day to maintain her current condition. 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.  

Your geographic location must also be considered when thinking about
selenium from feeds and supplementing.  As Heidi would indicate, her
areas in the Pacific Norhtwest are selenium-deficent.  Portions of
Idaho, California, portions of New Mexico/Arizona, Canada, northeastern
US, Florida, east coast, and Great Lakes regions tend to grow forages
deficient in selenium as well.  However, there are also areas in the US
(regions throughout the midwest and northern states) that can have
locally high accumulations of selenium in the soil, where you do not
want to supplement for this mineral.

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
toxicosis.  

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 (http://www.horsehealthusa.com or
info@horsehealthusa.com 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)