Ridecamp: Re: [RC] thumps (Technical response-long)

I'm going to disagree with Dr. Tomlinson about the storing calcium
comment--as I have a different take on it from dealing with calcium issues
in dairy cows.  Bear with me--this is somewhat scientific, I'll try to
explain it as I go:

The issue here isn't so much the ability to store calcium as it is to
remobilize it from storage (bones).  When an animal's body is unable to
mobilize it from their primary storage site rapidly enough (in cows, the
problem is related to the onset of lactation, but the biochemical mechanics
still apply, here), it "cheats" and takes it from muscle.  The larger
muscles (of course) are going to be more likely to be affected, since they
have more calcium in them.  In cattle, it results in "milk fever", or a
temporary paralysis--in other words, reversible--because calcium is
necessary for muscle contraction.

The original theory was that when an animal is getting adequate calcium from
the diet, as in alfalfa hay, it
stops mobilizing calcium from the bones.  In dairy cattle, we used to reduce
the calcium in the diet for the last three weeks of pregnancy to force the
body to start pulling calcium from the cow's bones.  Now we know that it's
not so much the amount of calcium in the diet as it is a function of
something called the "dietary cation-anion difference", or DCAD.

As you probably remember from chemistry class, ions are either positively or
negatively charged.  Interestingly enough, what researchers found out was
that when there was a positive difference (enough potassium and magnesium to
cause an overall positive DCAD in the blood compared to sulfur and
chlorine),  high-producing cows were more likely to develop milk fever.  If
they have a negative DCAD, milk fever isn't an issue--the calcium will be
mobilized more easily because positive ions are attracted by negative ions,
and calcium has a +2 charge on it....thus it is more likely to be mobilized
if the DCAD balance in the animal is negative rather than positive.

Now--why is this tied to alfalfa?  Not, as one would suspect, the calcium
content.  Instead, it's because of the POTASSIUM content in forages,
especially alfalfa.  High-potassium forages cause more problems with milk
fever than low-potassium forages.  It has gotten so difficult to get low
potassium hay (because fertilizer use is loading the soil with potassium)
that we've resorted to making mineral mixes designed to give a negative DCAD
to the diet, and thus stimulate calcium mobilization pathways (reverse the
storage pathways, essentially) to prevent the body from taking it from the
muscle in such large amounts.  How does this tie in with thumps in horses?
The diaphragm in a horse is a huge muscle, so I would expect it to be
susceptible to calcium loss just as the leg and hip muscles in a cow are
during the onset of lactation.  My guess is that the skeletal muscles are
creating such a demand for calcium for continued contractions that some gets
pulled from the smooth muscle of the diaphragm, and cause the fluttering
commonly called thumps.

This makes me wonder if perhaps this issue is what led to the MARE report
regarding potassium-free electrolytes.  I do have a couple of papers
regarding DCAD measurements in sedentary horses that I need to dig out and
study (If I can remember where I put them!  LOL)  One of these days I'm
going to get my hands on a copy of the MARE report and read it, too.
However, this doesn't mean I advocate stopping electrolyte supplementation
that y'all currently use---until there is concrete scientific proof that
this is related to thumps, my recommendations on electrolyte use are the
same as Susan Garlinghouse's.



----- Original Message -----
From: "DABNEY FINCH" <dabneyesq@xxxxxxxxxxx>
To: <greenall@xxxxxxxxxxxxx>
Cc: <ridecamp@xxxxxxxxxxxxx>
Sent: Wednesday, June 19, 2002 12:36 AM
Subject: Re: [RC] thumps


>     I am aboslutely convinced thumps are genetically predisposed.  Gary
and
> I had two full brother geldings who were both marvelous endurance horses
> EXCEPT that both were predisposed to thumps (esp. in hot weather--even
when
> other vet scores were all As) ; they also took a longer time to recover
at
> VCs than our other endurance horses.  None of our other endurance horses
> have ever thumped except these two brothers.
>     We finally arrived at a formula that worked, as tested in a
particularly
> hot Californios 100: LyteNow at half doses every hour.  (Higher in calcium
> than other e-lytes.)
>     Also, Mike Thomlinson, DVM, recommended to us once that the liquid
> calcium administered to cows was used for horses that tended to thump on
the
> international rides he vetted . . .  I tried it once as a precautionary
and
> thought it burned my horse's mouth, but it might be worth having around in
> the event of.  Hopefully not necessary if you follow the "little bit every
> hour"  approach.
>     Another thing Dr. Thomlinson told us was to limit alfalfa.  Just a
tiny
> bit daily, but then do feed more of it right before a race.  (Apparently
the
> horse's body learns its getting so much calcium from the alfalfa it
figures
> it doesn't need to store it, if you feed alot of it--I've done that with
> e-lytes fed on a daily basis and gotten in Big Trouble, so makes sense to
> me.)
>     Hope this helps!
>
> ----- Original Message -----
> From: "John & Sue Greenall" <greenall@xxxxxxxxxxxxx>
> To: <ridecamp@xxxxxxxxxxxxx>
> Sent: Tuesday, June 18, 2002 2:23 PM
> Subject: [RC] thumps
>
>
> > Can there be a "slight" case of thumps?  As in tying up, there are
> > degrees?  Will calcium always correct it?  Can a horse have a
> > "predisposition" for thumps (like tying up)?  So we have all heard
> > that electrolytes will "prevent" thumps, but is there a "magic
> > number" for the amount of Ca+ needed to do this?  And if the horse
> > is thumping, is there a source of Ca+ (such as cows get) that is
> > recommended for horses?
> > Yep, gotta new Morgan that seems to stress out in company and
> > "thump".  I think?
> > John and Sue Greenall
> > mailto:greenall@xxxxxxxxxxxxx
> > http://www.vermontel.com/~greenall
> >
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 Ridecamp is a service of Endurance Net, http://www.endurance.net.
 Information, Policy, Disclaimer: http://www.endurance.net/Ridecamp
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