I thought you all might be interested in this information from a
quite knowledgeable sorce... I've left the original poster's name &
website address link at the bottom, and am copying here with her
permission. It takes a bit of careful reading, fascinating
information, however.

Also note, in my discussion with BET labs they told me NEVER mix
Thyrol-L with water (as in to dose with a syringe), that for some
reason it will partially deactivate the Thyrol-L and significantly
reduce effectiveness. She indicated that its ok to slightly dampen
food if necessary, just don't try to actually make a water suspension
of it...

Here's the post from a breeding bulletin board when a hypothyroid
issue came up during discussion of lymphangitis:
____________________________________

I've talked with him, Ray LeRoy, wonderful biochemist. He's worked
with Dr. Sarah Ralston, VMD, in doing breakthrough nutritional work
on horses. Unfortunately he's now retired. His supplement One AC was
originally developed for people who cease sweating (called
anhydrosis) usually as a result of exposure to extremely hot humid
situations (which most of you won't believe but we actually have
hot+humid in the southwest during the second half of our very hot
summers). The FDA difficulties were such that he never wound up
marketing it for humans, instead he found out about horses in Phoenix
who were non-sweaters and decided to help them. It worked and he then
marketed it nationwide. (He told me last year that it was only about
$30 for a one month supply, don't know what it is now.) I don't have
a full list of ingredients but Ray told me that the supplement was
mainly an amino acid, L-Tyrosine, which is a precursor biochemically
that is converted by the body into Thyroxine (T4, a major thyroid
hormone). L-Tyrosine is a break down product of phenylalanine
metabolism and is usually in good supply in the body but if the body
does not process the phenylalanine correctly then it is left with too
little tyrosine for conversion into thyroxine. A second biochemical
pathway is what causes the main effect in anhydrotic horses, the lack
of tyrosine acts on both this second biochemical pathway which is
what leads to failure of the sweat glands, and ALSO on the thyroid.
This is why non-sweaters (anhydrotic horses) have BOTH the
hypothyroid symptoms and the anhydrosis. The end result is a horse
that is a little low in T4, T4 is converted into T3 (another thyroid
hormone) and since T4 is low T3 is also. The supplement also contains
some minerals to help with L-Tyrosine uptake and to stimulate the
conversion of phenylalanine into tyrosine. The result is that One AC
works for about 90% of all horses that are otherwise normal but cease
to sweat properly. For the other 10% of non-sweaters Ray suspects
that there is some other problem with the biochemical pathway and
therefore the supplement doesn't help.

What does all this mean? It means that if your horse is a non-sweater
(anhydrotic) and the supplement worked to get her sweating again then
she is indeed somewhat low in thyroid hormones also, however the
reason she is low in thyroid hormones is because of a breakdown in
the processing of phenylalanine into tyrosine. Why is it important to
know that? Because treatment with Thyro-L (thyroid hormones) is kind
of like a shotgun treatment, it shoots a big hole in things where all
you really need is a little tiny pin prick. This horse is also in
need of the supplement to get her sweating correctly, you see she is
showing two different symptoms and you are in essence only treating
one. Also when you treat with thyroid hormones you will by virtue of
a very complex feedback mechanism slow down the body's own production
of thyroid stimulating hormone and thyroid hormones. This is why if
you ever take a person or horse off of thyroid supplements you must
do so gradually and it may take as long as a year for the body to
recover its own ability to make the missing hormones (assuming it
can). It is unlikely that this horse has equine Cushing's-like
disease -- I asked Ray about this for one of my horses who may be
borderline Cushingoid-- which is a disease in which there is an
abnormality of either the pituitary (most common in equines) or the
adrenal glands (most common in humans, [see Robin I read the websites
you suggested :-]). In the case of equine Cushing's, as I understand
it, too much TSH (thyroid stimulating hormone) is produced which
leads ultimately to thyroid exhaustion, the thyroid ceases to respond
to the TSH and therefore is no longer producing sufficient thryoid
hormones. The key with that disease is to slow down the pituitary's
production of TSH (and other hormones) so that the thyroid can
recover and produce the correct amount of thyroid hormones. What Ray
told me was that Cushingoid horses are generally fine in the sweating
department, they have plenty of tyrosine to convert to thyroxine and
therefore his supplement won't help them. In other words a horse that
is a non-sweater is unlikely to be Cushingoid because even though one
symptom -- hypothyroidism -- is the same the causes of the two
diseases are different.

This is really a case of matching the disease cause to the treatment.

As for the lymphangitis, that's a nasty disease in which the initial
insulting event can be either an infection or an injury to the
lymphatic vessels which are then damaged. Lymph fluid can no longer
return to the central core of the body once it is pumped to the
injured lymph vessels and tends to pool there. Treatment is
symptomatic and results are not consistent. More research is needed,
and I think it is going to have to consist of how to restore function
to the injured lymph vessels, since that is what is causing the
disease.

In my opinion from what I've read it is not likely that the
lymphangitis is related to her being anhydrotic since there don't
seem to be reports showing horses with anhydrosis to be more likely
to develop lymphangitis. But that doesn't mean that it can't be
related, just not real likely. I don't know what to suggest about
breeding her. I know I would treat both the lymphangitis and the
anhydrosis as needed. I would also talk to your vet about the
anhydrosis, that can be a real serious issue with pregnant mares
since they have to rid themselves of both the heat of their own
bodies and that of their unborn foals. For myself I would prefer to
treat the anhydrosis with One AC rather than Thyro-L, One AC is
specific for both anhydrosis and tyrosine-deficient hypothyroidism
whereas the Thyro-L is only treating the hypothyroidism, and it's not
really going about treating the cause of the disease, just the
symptoms. But I'm not a vet, I suggest that you discuss it with your
vet and possibly ask if he would consider calling Dr. Sarah Ralston
at Rutgers University to discuss the issue with her, she's the top
equine nutrition expert in the country IMO and very approachable
(she's also an endurance rider who shows up occassionally on
endurance-l and is Internet accessible).

I hope this rather lengthy discussion is somewhat helpful.

Tracy Scheinkman Misty Mountain Arabian Sport Horses Tucson, AZ

http://hometown.aol.com/Arabs4sprt/Arabs4sprt.html