Re: Nutrition

["Duncan Fletcher" <dfletche@gte.net>]

NRC gives 2 mg/kg of diet (dry basis) as the maximum tolerable dose for
selenium. Selenium toxicity can be chronic, low overdoses over a long
period;  or acute, high overdoses in a short time period. The resulting
toxicity is quite different in the 2 cases: loss of hair and hoof wall in
chronic (alkali disease) and stumbling; breathing and cardiac abnormalities,
and colic in acute (blind staggers). The real question is what is the
general selenium content of your feeds: hay, etc. For that, contact your
county extension agent.

Copper interacts with a number microminerals and radicals: molybdenum,
sulfate, zinc, selenium, silver, cadmium. Copper can be used to depress
selenium absorption in areas with high selenium content in the feed. There
are undoubtedly many other interactions of which we have no knowledge. The
problem with trying to micromanage these nutrients (aside from incomplete
knowledge) is that there is no good source of information as to the content
of the normal forages and grains fed horses. The NRC tables are useful for
those minerals that remain more or less constant in a given plant species,
but are useless for  those minerals that vary greatly: selenium and
magnesium are 2 that come to mind, but I am not certain that some of the
others aren't also as variable. Even for the others, the tables are based on
very small number of samples and variations exist.

It is possible to test your hay, but I have never seen routine hay tests
include anything beyond crude protein, DE (calculated from protein and the
various fiber types: ADF, NDF), calcium, phosphorous and perhaps selenium
and potassium. Those can be done fairly reasonably, but I haven't a clue
what it would cost to include all the other nutrients. The form of the
nutrients is also another variable that would ratchet the testing up another
notch. Of course, if you are feeding grain, that would also have to be
tested. Since most supplements seldom give you a maximum and minimum level
of the nutrients, you again have no way to calculate the balance. For most
nutrients, a minimum level is given - there is no way of knowing the
maximum.

The bottom line is not to try and do the impossible: micromanage the
micronutrients. Pay attention to the big ones and hope for the best. As a
general rule, I do not like the practice of giving multiple supplements
without very good reason: the chances of mucking something up is probably as
good as the chances of doing something useful. It is possible to find biotin
and amino-acid supplements without adding the minerals.

In some cases, the addition of some of the nutrients into a formulation is
done strictly for marketing reasons: they want the ingredient listed on the
label. If it is there in an amount of say less than 10% of the horse's
requirements, it is there for marketing purposes - not for any nutritional
reason. If the horse normally receives all his requirements from hay (e.g.,
iron and potassium), the nutrient is also there for marketing.

Happy to hear you and the critters survived that ordeal.

Duncan Fletcher
dfletche@gte.net

-----Original Message-----
From: Lysane Cree <cree_l@LSA.Lan.McGill.CA>


<<
I have a couple of questions about nutrition:
1)How much selenium is
too much? And what does too much selenium do exactly?
I just bought a bag of pre-mixed grain (like Omolene -oats,
corn, molasses, and other goodies) and noticed that there is
selenium in it. The vitamin/mineral supplement which my horse gets
about twice a week [in the winter-such as now-he always eats all that I
give, in
the summer he sometimes leaves the supplement]
also has selenium in it. The amounts which are indicated on the bags
(I can't remember how much exactly offhand) are calculated as "per
kg". Of course my horse is not getting a kg of the stuff, but only a
scoop at feeding time twice a week, which would be no more than a
couple of ounces. So how much selenium is he actually getting in
those few ounces/week, I have no idea! Which is why I am wondering
about this and whether I am creating a problem here..

2)I have purchased some Farrier's Magic (same idea as Farrier's
Formula) to add some biotin in my horse's diet. There is also copper
and zinc in Farrier's Magic. Now, my regular vitamin/mineral supplement
also has copper and zinc in it. I have read that copper and zinc need
to be balanced (in a similar fashion as calcium and phosphorous need
to be balanced). Again, numbers are calculated as to what is in the
entire container of Farrier's Magic (an 11 pound container).
The scoop in that case has written on it 60 cc and you are supposed to
feed 4 of those scoops/day. My question is whether I should be
feeding both the Farrier's Magic and the vitamin/mineral supplement
at the same time?  or should I not feed the vitamin/mineral supplement
when I feed Farrier's Magic (or vice versa)?
Help!
[snip]
>>