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What happened at 20 MT:

I pulled my horse at 92 miles of the 100 because though all of her
parameters were well within the normal range, and the Duck (and Charlie
who was also at that vet check) said, "Your horse is easily within the
range of normal parameters so you can go on, but she is moving
differently in the hind end than I normally see this horse, so it is up
to you." (and they had both seen her quite a bit since they had just
vetted her a couple of months earlier for the 200 miles at Death
Valley).  I elected not to go on at that time, not because I thought
there was something seriously wrong with her but rather because while
riding her I could tell that her reactions weren't quite as quick as she
normally is and figured she was just kinda tired from the mileage
(further than she had ever gone before in one day), but I didn't want
her to trip in the dark from being tired and seriously injure herself
because she couldn't catch herself easily.

We trailered her back to camp, she got out of the trailer rather slowly
(but she HAD just gone 92 miles, so I figured she had earned the right
to move a little more slowly), and I took her back to the trailer where
she ate and drank, peed and pooped all night long.

The following morning, she could barely move.  Not because she was
stiff, or sore, but because it was like there was a neurological
disconnection between her brain and her feet.  If I kinda pulled her off
to the side to unbalance her a bit so she could get the first foot
moving, she then was a bit clumsy for the next stride or so, and then
trotted out just fine, but lost her balance through a turn, and if she
stopped, I would have to unbalance her again to get her to be able to
move.  All of her metabollic parameters were still normal, including her
heart rate (although we didn't do a CRI because we didn't want to make
her move that far)...maybe a little elevated (high 40s to low 50s).

When the Duck came over to look at her, he said, "I don't have a clue
what is wrong with this horse, I have never seen anything like this
before, but I think we need to get some fluids into this horse."  So we
did.  About half way through the second 6 liter bag, she peed (normal
color).  And though she got some rather wierd edema in her chest,
forelegs (not lower legs) and a little bit in her nose, she now appeared
brighter eyed and seemed to be able to move normally.

He pulled blood on her (and gave it to me to take back to have my vet
run it since I was going to be the closest to a lab the soonest) and
suggested that I have her checked for EPM and maybe some other
neurological diseases when I got the chance.  He had also pulled blood
on her before he started the IV, but it got left out on the hood of his
truck while we started the IV so that batch got thrown out. We discussed
whether it was best to leave the horse in Ridgecrest or to take her home
(~ 3 hr trailer ride) while she was apparently stable.  And decided to
take her home (actually to my crew's place in Chino Hills, less than 1
mile from Chino Valley Hospital which, if she were to go south rapidly,
would where she would be taken to from Ridgecrest anyway).

When she got off the trailer, she still had a bit of the odd edema
(although less so and it appeared to be gone from her nose), and she got
off the trailer as if the odd ataxia had never existed; although she was
still a bit tired.  I made arrangements for her regular vet to come out
and see her the following day (Monday) and to give him the blood to run
a full chem panel.

When he came on Monday, there were no signs of any of the ataxia or the
failed proprioception tests, the blood work showed that she was mildly
hyperkalemic (which may or may not have been significant, since serum
potassium levels rise the longer the blood sits around before being
tested), her CPK was elevated (17430, which is more than I had seen in
blood work I had had done on her at rides before as part of Barney's
PRIDE project, 3,000 or 6,000 but less than Barney has seen on many
other horses that have completed without any ill effects) and her AST
was also slightly elevated (825, also slightly more than previous PRIDE
project numbers 400-600).  And AST levels weren't high enough to
indicate a serious tie up. She also had an elevated Bilirubin (3.8) but
not a high GGT (5.7).

I have the advantage of having lots of blood work on this horse
(including pre-ride and just pre-treatement for the NC 100, since I had
made arrangements with Barney to do  "before/during/after" blood panels
on her, despite the fact that he no longer has his machine, since I am
one of the few people who was interested in doing it).

The blood panel of the pre-ride sample (run on the same machine as the
sample that was taken just prior to her fluid treatment) showed
everything sorta right in the middle of normal range.  To quote Barney,
"If I were going to start an endurance ride on a horse based on its
blood chemistry, that is the one I would want to start on."  And we
pulled the blood before the IV treatment (which the vet had added Ca,
Ph, & Mg to in addition to the normal fluids, but no drugs) and the only
things that were outside the range of normal were:  Total Billirubin
(3.1) although GGT was 6 (so it is unclear to what extent that may
indicate liver problems); her blood glucose was high (156) so that ruled
out hypoglycemia (which is one of the things we considered) and her Ca
was 12.5 higher than the 12.0 of the pre-ride sample, and within the
normal range of 11.5-14.0 so it is unlikely that it was lack of the
electrolyte Calcium that was the culprit).  The machine that was on site
didn't test Na, Cl, or K (too bad), and none of her blood work has ever
check Mg (and she has never been orally supplemented with Mg during any
ride, so maybe she has a Magnesium deficiency...and one of the symptoms
of Magnesium deficiency is ataxia so....?????)

At her first ride after 20 MT (Mt. Charleston 75 where we went off
course and did closer to 83 miles....yes, we were WAAAAAAAAY off course,
following ribbons that had been put out by a different group :)), I had
Barney pull blood on her before, during, and after, and this was when he
still had his machine.  She completed the ride (top ten, although that
doesn't mean ALL that much when there are only about 15 starters)
without incident and the electrolyte levels were totally normal (she had
been electrolyted in pretty much the same way as I did for the NC ride
although not the same as I had for 20 MT since one of the vets who
looked at her said, "She almost looks a little hyperkalemic." At 20 MT
she had been electrolyted much more agressively earlier on in the ride
with a commercial electrolyte mix that contained both NaCl and KCl as
well as Ca and Mg.  Since hay contains huge quantities of Potassium, I
decided to take potassium out of her oral electrolytes and alfalfa hay
and beet pulp (both of which she eats during a ride) also contain large
quantities of calcium I didn't feel the need to supplement those
either.)

In the interim she had also completed all four days at Death Valley, all
three days of the Cuyama Oaks XP (in the top 10 out of as many as 100
riders, so more significant, but still just jogging along).

She had previously also completed rides in Kansas and Nebraska in the
summer (electrolyted also, with just salt and what she could get from
her feed) with heat and high humidity without incident.

In this most recent experience, she had only had about half of the first
5 liter bag of fluids before you could pull on her tail and she would
resist (which she wouldn't do before the treatment was started), and
when the first five liters was done, the vet asked what I wanted to do
(since she was now looking fine) and together we decided that since the
catheter was in and she was standing quitely and eating while she
received the treatment and that no horse was ever hurt by getting more
IV fluids, to put another 5 liters into her (this preparation did not
have the Ca, Mg, Ph added to it).  After this, she peed almost
immediately.  She also pooped while she was tied to the trailer getting
her fluids and it was "pretty much normal, maybe a little on the dry
side."

What I am dealing with here is a horse that on two occasions has been
ridden fairly conservatively, has taken good care of herself throughout
the ride, continues to eat, drink, pee, and poop normally, has totally
normal metabollic parameters (even when she could barely move or you
felt you could push her over with one finger) although her heart rate
does stay slightly elevated (mid 40's to low 50s), that "trots out of
it" if you can just get her through the first couple of steps where it
appears that she doesn't know where her feet are.  She has tested
negative for EPM and has never shown any signs of this except on these
two occasions despite over 1000 miles (that's how we qualified for the
NC) of successful competition where she has finished in the top ten of
large rides by jogging her way through them.

I also have four very experienced endurance vets (Dave Nicholson, Jamie
Kerr, Barney Flemming, and this guy from Texas whose name I can't
remember), the treatment vet (who doesn't have quite as much endurance
experience as these other guys), and my own vet (who is also the vet for
Joan Irvive-Smith's Grand Prix show jumpers and the official vet for all
of the Show Jumping Grand Prixs at the Oaks) who have, "Never seen
anything like this before."

Clearly, I rode her beyond the level of her condition to be able to
handle what I asked of her, but it is also beyond me what might be going
on with this horse that might be causing it (so that I might know what
to do differently next time).

I have an appointment with my own vet next week to have him look her
over.  I will be having her tested for selenium deficiency (unlikely
here in the SW, but she just 3 months ago changed over to getting some
timothy hay in her ration....which comes from the PNW, so maybe selenium
is a factor.  I will be having the hay tested too.)  And I will ask him
about checking her magnesium levels.

However, the other thing that these two rides had in common, is that for
these rides she was WAAAAAY fitter, cardiovascularly than she has been
on other rides and I wonder if her rapid HR drop and low HR leads to
hypotension (I have hypotension myself, and post exercise I too will
"black out" and it will take me a few seconds to be able to figure out
where my feet are), but this doesn't explain why spending 6 hours tied
to a trailer eating, drinking, peeing and pooping (and getting oral
electrolytes that DID include potassium, calcium, and magnesium) does
not resolve the issue but rather makes it worse, while 6 liters of
fluids does????

Her working heart rates at the NC were what I would consider to be
abnormally low (but I have never heard of that being a bad thing);
however, if it is hypotension, maybe she needs lots more salt than I am
giving her???  I asked the vet from Texas if it is possible to take a
horse's blood pressure (he said that some people were doing it by using
a human BP cuff around the horse's tail, but when I asked him what is a
normal blood pressure for a horse, he said he didn't know).  Does
anybody else know anything about hypotension in horses?

Does anybody else know anything at all about long-term, low intensity
(and trust me, this was MUCH lower intensity work that what we train at
and what she is capable of) exercise induced ataxia....that can be
resolved with an almost insignificant amount of IV fluids in a half an
hour, but can't be resolved by gallons of oral fluids and oral
electrolytes over the course of 6 hours?

It isn't that she hasn't worked in the heat before (Mt. Charleston in
May is not reknowned for its cool temperatures, nor is Kansas in June)
and I had been heat conditioning her in preparation for this event (we
have had a few hot days around here in the last couple of months and she
was the horse that I took out in the heat of the day and worked at much
higher intensity than this), it isn't that she hasn't done difficult
rides before.

I can't speak for any of the other people at the NC 100 ride (although,
since I was there, my observations are probably going to be more
accurate than the speculations that many of the other commenters here
have made, so I will leave it to the others whose horses were treated to
share what may or may not have been the cause for them).  I still
haven't figured it out for my horse, and I would like to, because she
really is quite skilled as an endurance horse. But unless somebody can
come up with an explanation of why this happens to her and how I might
reasonably stop it from happening again, I will probably have to retire
her from endurance.

If anybody has any ideas on what it is that may be going on with this
horse (or if they have seen it themselves???), I am all ears.

kat
Orange County, Calif.

p.s.  My average riding speeds for each leg were:

The first 12 miles in ~1:45 ( 6.8 mph)
12 miles to 34 miles in ~ 3:30 (6.2 mph)
34 miles to 58 miles in ~ 4:00 (6 mph)




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