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[RC] magnesium? - Duncan McLaughlin

Heidi wrote:
?On the other hand, the reason that it works as a
laxative is because it isn't absorbed and therefore
pulls fluids back into the bowel--so it isn't doing
you any good as a magnesium supplement, either. And
even though you might have to give more than you're
apt to put into an e-lyte mix to have an appreciable
laxative effect on a constipated horse, it is still
not a very smart thing to put into a horse's gut when
you're trying so hard to get fluids from the gut into
the circulation and cells.?
----------------------------------------

It is too simple to say: the reason magnesium salts
work as a laxative is because they are not absorbed
and that they pull fluids back into the bowel.

Magnesium absorption is primarily controlled by its
level in the blood and there are two factors, the form
of delivery and the dose rate, that affect uptake:
1. Generally, uptake (bioavailability) of salts,
including magnesium runs from lesser to greater as
follows: carbonate, sulfate, acetate, citrate. That
is, citrates are more available than carbonates.
2. The rate of uptake is inversely proportional to the
dose. If you give a small dose of magnesium, most of
it (around 70%) is absorbed. If you give a large dose
of magnesium, little of it (down to 20%) is absorbed.

There are a whole bunch of factors (including presence
of other minerals, plant phytates, stomach pH and so
on) that also affect magnesium uptake.

But generally, if serum magnesium level is low and/or
falling, magnesium will be absorbed (actively
transported), irrespective of hydration. If a small
amount of bioavailable magnesium is used (as per
commercial electrolyte mixes) this will be taken up
and there is no risk of drawing fluid from circulation
back to the gut. 

The risk occurs only if the magnesium dose is too
large and/or not available. If this is the case you
are going to have far more serious issues arising from
the other electrolyte salts that are present in,
absolutely and proportionally, much larger amounts.

And although excessive magnesium salts can lead to
diarrhoea, diarrhoeacan also be a symptom of magnesium
deficiency. The key is to use the correct amount.

Cheers
Dunc












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