Following is a letter/paper written by Dr. Gary P. Carlson, DVM as a
summary of the testing done on horses during the 1996 Western States
Trail Ride held July 27, 1996. We are sharing this with the endurance
community so we can all benefit from Dr. Carson's observations.
Enjoy,
Larry Suddjian, Ride Director
WSTR
http://www.foothill.net/tevis
GARY P. CARLSON DVM, Ph.D., Professor
Department of Medicine and Epidemiology School of Veterinary Medicine
University of California
Davis, CA 95616
12 December 1996
Dear Western States Trail Ride Board of Governors,
We would like to take this opportunity to thank you for graciously
allowing us to participate in the 1996 100 miles one day Ride in a
research capacity. This year again we supplied "trail-side" laboratory
support for check point veterinarians attending horses removed for
medical reasons. We also collected samples from "normal" competing
horses to provide a reference point so we can reliably interpret the
data. The purpose of the study that you funded was to (1) establish
"normal" values for this Ride, and (2) compare the values of horses
removed for medical reasons to control values. The laboratory values
that we examined included total protein, hematocrit, and serum
chemistry. We would like to acknowledge the generous support of Mr.
Bill Johnson from CVD laboratories who processed much of our laboratory
data at no charge to us.
Blood samples were drawn from 21 horses at Robie Park the day before
the Ride. Owners and trainers (often the same individual) were briefly
informed of the intent of the project and that we wished to draw two
samples during the Ride at rest points (Robinson Flat, Michigan Bluff).
Ride participants were very supportive. Concerns voiced by a few
related to:
(1) side-effects to the horse, mostly pertaining to the volume of blood
to be drawn, and
(2) whether or not the data would be made available to them.
Fewer than twenty milliliters of blood, a negligible amount, were drawn
at each sampling. Fourteen riders were interested in receiving a copy
of the data; copies were mailed to these Ride participants with an
invitation to call us should they have any questions. Additionally,
they were encouraged to review these results with their veterinarian at
home.
As previously mentioned, samples were drawn at Robie Park the day
before the Ride, and then at Robinson Flat and Michigan Bluff, the day
of the Ride. A hematocrit, total plasma protein (TPP), and serum
biochemistry panel were obtained from every sample. The hematocrit and
TPP are reflective of hydration status. A serum biochemistry profile
provides information on the following: serum electrolytes; enzymes from
muscle and liver (which will be elevated if these organ systems are
compromised); and other products of metabolism, primarily from the liver
and kidney (which are also elevated if these organ systems are
compromised.) Samples were obtained from 21 horses at Robie Park, 12
horses at Robinson Flat, and 20 horses at Michigan Bluff. Of the 21
original horses sampled at Robie Park, 4 had samples drawn at Robinson
Flat, and 18 had samples drawn at Michigan Bluff. The additional
"non-original group samples" obtained at Robinson Flat and Michigan
Bluff were largely from horses removed for medical reasons.
The following is an interpretative summary of the data. Of the 21
original horses sampled at Robie Park, 14 were accepted as controls
("normals") at Michigan Bluff. These 14 horses had no marked elevations
in their blood work and passed the "vet check". When compared with data
obtained from the 1974 Ride, a difference in trend with respect to
sodium is observed. In 1974 serum sodium levels progressively decreased
throughout the Ride. In 1996, a significant increase in the mean
(average) serum sodium level was observed between the Ride samples taken
at Robie Park and the samples drawn at Michigan Bluff. In fact, in all
of the control horses serum sodium increased (range 1 to 14 mEq/L).
Additionally, a significant difference in trend was observed in serum
chloride levels. Although mean serum chloride levels decreased in this
year's data (-2.2 mEq/L), the decrease was much less dramatic than the
one observed in 1974 (-11 mEq/L). Increased electrolyte supplementation
or decreased electrolyte losses in sweat or a combination of the above
may explain these changes in serum electrolyte values. It is important
to note that although there was a significant difference in electrolyte
values between this Ride and the previous study, the general trend for
dehydration reflected in TPP, hematocrit, BUN, and creatinine values was
very similar.
Five horses were pulled at Robinson Flat. Of these five, two horses
had greatly elevated muscle enzyme levels indicating that they were
"tying up". Two had signs consistent with colic and one appeared
exhausted.
Two horses were pulled at Michigan Bluff. One was colicky, the other
was fatigued. Neither one had significant elevations in muscle
enzymes.
Horses that had non-metabolic reasons for being pulled, or had
unusually abnormal bloodwork but nevertheless completed the Ride were
excluded from the control group. One horse was eliminated from the Ride
at Michigan Bluff for lameness. His bloodwork, however, was normal. A
second horse was eliminated after the Michigan Bluff check point for
lameness; this horse had markedly elevated muscle enzymes, indicating
muscle damage. A third horse finished the Ride within the top thirty.
Blood was drawn from this horse at Robinson Flat and Michigan Bluff.
The horse had tighter muscles than normal as reported to us by the owner
at Robinson Flat; however, the horse recovered well and did not seem
painful. The horse was judged to be clinically normal by Ride
veterinarians and was permitted to continue. Interestingly, this horse
had markedly elevated muscle enzymes, indicating muscle injury. The
bloodwork is consistent with rhabdomyolysis (tying up); however, the
horse did well clinically. We did speak with the owner regarding these
findings.
The main finding from this data is the difference in electrolyte values
when comparing present values with values of previous Rides.
Interestingly, the trend for an elevation in sodium levels and
relatively little decrease in chloride levels during the course of the
Ride (as opposed to a marked decrease in both) contrasts with previous
reports in the literature of other rides as well as data from previous
"Tevis Cup" Rides. Although the reasons for this are unclear, there
are several possibilities. One is an increased use of electrolyte
supplementation. This may relate to more horses receiving electrolyte
supplementation than before, higher doses, more doses being used during
the Ride (higher frequency), or a combination of the above. A second
may be the use of improved formulations. A third may be decreased sweat
losses, although this seems very unlikely. A fourth may be an increase
in the practice of supplementation prior to the Ride, i.e., "loading up"
before the Ride.
In a controlled study performed in 1995 by Dr. Coenen et al. in
Germany, it was suggested that water and electrolyte metabolism can be
improved if electrolytes are administered before long-lasting exercise.
In this case, the supplement was administered four hours before the
exercise. It should be pointed out as well that Dr. Coenen exercised
these horses for two hours only on the treadmill; a direct comparison
may be inappropriate.
Although we had few horses removed for medical reasons during the Ride
which makes interpretation of these particular results difficult, the
difference in trend for measured sodium and chloride concentrations is
noteworthy and merits further consideration and study. We have also
noted slightly different normal resting pre-Ride values in our horses
which relate in part to different laboratory procedures used for
electrolyte analysis. The present study provided some much needed
information to help resolve this potential area for confusion.
We would again like to thank you for your support. These data will be
examined more closely and compared with other studies on this and other
Rides. We plan to distribute the data in its entirety to the Ride
veterinarians through Dr. Mitch Benson for their comment. If you have
any questions about our studies, do not hesitate to ask. I am sorry I
have been unable to attend the last few board meetings as I have had
prior commitments.
Sincerely,
Gary P. Carlson D.V.M., Ph.D., DACVIM
NOTE: THE FOREGOING PAPER HAS BEEN EDITED TO PROTECT THE ANONYMITY OF
THE RIDERS AND WAS EDITED WITH THE FULL PERMISSION OF GARY P. CARLSON,
D. V. M., Ph.D., DACVIM