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THE EFECTS OF COMBINED RIDER AND TACK WEIGHT ON THE LACTIC
ACID PRODUCTION IN THE HORSE ( Equus caballus) AT THREE
DIFFERENT GAITS: WALK, TROT, AND CANTER.
Anahita A. Ariarad and Allison S. Lindsay
Department of Biological Science
Saddleback College
Mission Viejo, CA 92692
During glycolysis, L-Lactate is produced from pyruvate via the enzyme lactate
dehydrogenase (LDH) during normal metabolism and exercise. Due to increased
recruitment of skeletal muscle during exercise, it was predicted that lactate levels in
the horses would increase when the combined weight of the rider and tack was
added. To test this, blood lactate levels of five horses were taken before exercise and
again after walking, trotting, and cantering for various lengths of time. There was
found to be a 37.5% increase/decrease difference (say increase/decrease OR
difference, this is redundant) between the values of the canter when comparing
unmounted versus mounted blood lactate levels (p = 0.026, Tukey Correction). This
data partially supports our hypothesis, but further investigation is needed.
Introduction
Lactic acid is produced in minute amounts during rest but in greater quantities
during intense exercise. It is naturally present in humans as well as animals. When the
oxygen level in the body is normal, carbohydrate^s breaks down into water and carbon
dioxide. When the oxygen level is low, carbohydrate^s breaks down for energy and
makes lactic acid. Lactic acid is formed from glycogen by muscle cells when the oxygen
supply is inadequate to support energy production (Wickler and Gleeson, 1993). Buildup
of lactic acid in the muscle occurs only in (during might be a better word here, rather than
in) short bouts of exercise due to high intensity and it is usually correlated to fatigue,
exhaustion and muscle soreness. During aerobic exercise, the heart and lungs supply
adequate amounts of oxygen to the body for energy. Anaerobic exercise forces the body
to demand more oxygen than the lungs and heart can supply. This shows that the energy
supply is less and thus causes a high lactic acid level in the blood. (This sentence doesn’t
really make sense) Typically anaerobic exercise forces a person to slow down because
lactic acid build up causes moderate to severe muscle throbbing and rigidity. In human
athletes, ATP production in (lower-case g) Glycolysis may be as high as 3mMol/g body
weight x s (Newsholme & Leech^, 1983), and although similar estimations from equine
muscle are unavailable, the comparison of the activities of key glycolytic enzymes in
equine muscles to those in human muscles (Essen-Gustavsson et. al. 1984, Henriksson et.
al. 1986, Roneus et. al. 1991, Cutmore et. al. 1993) indicates that anaerobic ATP
production may be equally important in horses. Lactic acid gathers in the muscles when
the supply of oxygen is scarce for the oxidative processes and quickly diffuses out into
the blood stream. As lactic acid diffuses out of the muscles and other tissues, it appears in
the blood as lactate. Blood lactate can be useful for evaluation ^of performance. Lactate,
which is produced by the body all day long, is re-synthesized by the liver from glucose
that provides the body with energy.
In most mammals, lactate formed during exercise is oxidized to carbon dioxide
and water (Wickler and Gleeson^, 1993). Under extreme conditions, horses contracting
muscles are fueled by aerobic and anaerobic metabolic processes. When a horse performs
or exercises, they use their muscles to accomplish tasks. (You probably don’t need to say
this, as it is obvious) As lactic acid is produced in the muscles it leaks out into the blood
and is then carried around the body. (You already said this) If this condition continues,
the functioning of the body can then become impaired and the muscles can fatigue very
rapidly. When oxygen becomes available, the lactic acid is converted to pyruvic acid and
then into carbon dioxide, water and ATP (Kobayashi^, 2007). Horses performing low
intensity exercise for long periods lose large amounts of sweat. Lower intensity exercise
uses oxygen to provide energy, and is known as aerobic exercise. (You might want to
give this definition earlier in the paper, before you discuss the effects of aerobic exercise)
Aerobic exercise does not produce high levels of lactic acid. Muscles in horses secrete Dlactate as a by product (one word) of energy production during anaerobic exercise. In this
study, the effects of exercise and the cause it has on the increase of ^on blood lactate
levels in horses was tested. The objective was to determine if lactic acid levels in the
horse (Equus caballus) increase^d between mounted and unmounted at each gait. It was
expected that there would be a difference amid the blood lactate production between
mounted and unmounted (unmounted is not actually a word) after all three gaits.
Materials and Methods
Five horses were used in this study to determine if the combined weight of the rider and
tack has a significant affect sp. on blood lactate levels after walk, trot, and canter. All testing
took place at the J.F. Shea Center for Therapeutic Riding in San Juan Capistrano, California
under the supervision of a board-certified vet, Dr. Richard Markel. The horses were chosen for
testing based on size, temperament, and soundness. This information was available in their
medical/ health records and known by staff. Horses were removed from their stalls one at a time
and a fresh, sterile needle was inserted into the jugular vein. The first two drops of blood were
discarded before the base level sample was taken and read by the Lactate Scout (Sports Resource
Group, Inc.).
Over a period of a week, all five horses were lunged (define this word) on a line by a staff
member in a twenty meter diameter round pen. Each horse walked and trotted for fifteen minutes
at each gait, and cantered for six minutes. (Define walking, trotting and cantering.) Blood was
taken in the same manner as before and analyzed by the Lactate Scout immediately after each
gait.
From 8 November to 10 November 2009, all horses were ridden in the same tack (define
tack) and by the same rider to reduce variability in weight. Horses were ridden for the same
amount of time (what amount of time?) at the walk, trot, and canter as in the unmounted tests.
Blood was taken and analyzed in the same manner as before. All horses were then weighed using
Blue Seal Horse and Pony Height and Weight Tape (Blue Seal Feeds Inc., Lawrence,
Massachusetts). All data were transferred to MS Excel (Microsoft Corporation, Redmond,
Washington) where data were analyzed by ANOVA and Tukey Correction (if p ≤ 0.05).
Results
The mean unmounted blood lactate level at the walk was 0.0005 ± 1.13 x 10-04 mM•L1
•kg-1 (±SEM, N=5), at the trot was 0.0004 ± 8.9941 x10-05 mM•L-1•kg-1 (±SEM, N=5), and at
canter was 0.0008 ± 9.853 x 10-05 mM•L-1•kg-1 (±SEM, N=5). The mounted blood lactate level at
the walk was 0.0003 ± 4.17 x 10-05 mM•L-1•kg-1 (±SEM, N=5), at the trot was 0.0003 ± 2.1 x1005
mM•L-1•kg-1 (±SEM, N=5), and at the canter was 0.0005 ± 8.25 x 10-05 mM•L-1•kg-1 (±SEM,
N=5). As seen in Figure 1, between the groups, no difference was found when comparing
mounted and unmounted values in the walk and trot (p = 0.164 and p = 0.348, respectively). In
the canter group a ^significant difference was found (p = 0.026). Within the groups, a difference
was found between the unmounted values for trot and canter (p = 0.007), and the values for walk
and canter (p = 0.044). Similarly there was a difference found between the mounted values for
trot and canter (p = 0.006) and walk and canter (p = 0.028). This section should be justified.
0.001
0.0009
mM • L-1 • kg-1
0.0008
0.0007
0.0006
Unmounted
0.0005
Mounted
0.0004
0.0003
0.0002
0.0001
0
Walk
Trot
Canter
Figure 1. Mean combined lactate levels at walk, trot and canter unmounted versus mounted. No difference was
found between unmounted and mounted blood lactate levels in the walk and trot groups. A difference was found
between unmounted and mounted blood lactate levels in the canter group (p = 0.026, Tukey Correction).
Discussion
Lactic acid is capable of releasing energy to re-synthesize adenosine triphosphate (ATP)
without the involvement of oxygen. Lactic acid is produced from pyruvate in the glycolysis cycle
via the enzyme lactate dehydrogenase (LDH) during normal metabolism and exercise. The
amount of lactate present after exercise can be a helpful tool in determining performance because
it is an estimation of aerobic capacity (Poso, 2002).
Within the unmounted group, no difference was found between the walk and the trot
values. However, the trot to canter and walk to canter comparisons showed a significant
difference in blood lactate values.
Similarly within the mounted group the walk to trot comparison revealed no difference,
where the trot to canter and walk to canter assessments discovered a significant difference.
The hypothesis for this project stated that blood lactate levels would be higher at all three
gaits while mounted versus unmounted. However, collected data showed that blood lactate levels
were higher in the unmounted group. No statistical difference was found when comparing the
mounted and unmounted levels in both the walk and the trot. This is most likely because the
animals were not pushed into a state of anaerobic respiration at these gaits. For this same reason,
there was a difference found in the canter values between the groups. Though there are several
variables that can be taken into account when examining blood lactate levels, the researchers
believe that the results in this experiment could be explained by looking at the level of energy
applied when comparing exercise by lunging versus riding. During the unmounted testing, horses
showed a higher energy exertion at the trot and canter when compared to the mounted testing.
This is evidenced by the amount of forward momentum at each gait while lunging versus under
saddle. Though the researchers did not measure the velocity of each animal was not measured
(wasn’t in passive voice), obvious differences were observed while testing. Though it is possible
to push a horse into a higher energy level while mounted, our rider did not attempt to do this.
Though this experiment did find a significant difference, the relationship between blood
lactate production and increase in load (?) was opposite to what was originally hypothesized. In a
study to determine lactate minimum speed (LMS), the individual lactate production and removal
rates, in horses, Gondim et al. (2007) found no difference in blood lactate concentration at rest
and at LMS, despite an increase in heart rate. The data found in both these studies is inconsistent
with the majority of information available on blood lactate. LMS has previously been tested in
basketball players and runners (Tegtbur et al., 1993), in swimmers (Ribeiro et al., 2003) and rats
(Voltarelli et al., 2002) as well. In all the above studies lactate levels at LMS were significantly
higher than those at rest (Gondim et al., 2007).
All of the above experiments indicate that there exist one or more key differences in the
processing of post-exercise lactate in humans and equines. There are several factors that can
affect the lactate concentration in blood and these ^ factors need to be accounted for when blood
lactate measurement serves as a marker of performance. The rate of lactate production in
exercising muscle is influenced by oxidative capacity and thus training, which is often
accompanied with an increase in the number of mitochondria, may reduce lactate production
(Poso, 2002). On top of this, horses already have a marked increase in oxygen consumption with
a maximal oxygen uptake of about 160 ml/kg body weight × min (Evans & Rose 1988, Rose et
al. 1988). This is more than twice the uptake in human elite athletes (Poso, 2002). Training can
also increase the monocarboxylate transport proteins in the sarcolemma (Poso, 2002, Hashimoto
et al., 2008, Brooks et al., 1999). This allocates for a faster rate of facilitated diffusion and
therefore would add to the lactate concentration. The quantity of lactic acid that is permitted to
build up is determined by the effort that is needed to increase the lactate concentration to levels
above its resting value. This occurs when anaerobic glycolysis produces lactate at a greater rate
than the animal’s capacity to remove it (Gondim et al., 2007). In skeletal muscle, the fast-twitch
glycolitic fibers are mainly producers of lactate while the slow oxidative fibers act as consumers;
and therefore these two fibers, along with other factors, are responsible for creating the net
change in lactate levels (Hashimoto et al., 2008).
Acknowledgements
We would like to thanks the J.F. Shea Therapeutic Riding Center for allowing us the use
of their facilities, horses, medical supplies and time of their staff, with a special thanks to
Richard Markel, DVM. We would also like to thanks the following people for their assistance
and input to this project: Professor Steve Teh, Aaron Ko, and Amir Zand.
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Review Form
Department of Biological Sciences
Saddleback College, Mission Viejo, CA 92692
Author (s): Anahita A. Ariarad and Allison S. Lindsay_______________
Title: The Effects of Combined Rider and Tack Weight on the Lactic Acid Production in the
horse (Equus caballus) at Three Different Gaits: Walk, Trot and Canter
Summary
Summarize the paper succinctly and dispassionately. Do not criticize here, just show that you understood the paper.
In glycolysis, L-lactate is produced from pyruvate. It was predicted that with increased weight,
and therefore increased effort, more lactate would be produced when a rider and saddle were on
the horse during exercise. Buildup of lactic acid occurs during bursts of energy. It has been
shown that this is important in humans, and so it can be assumed that it is important in horses.
The point of this project was to determine if there was a difference in blood lactate levels in
mounted verses unmounted horses.
Five horses were used. There blood lactate levels were tested before and after testing. A
significant difference between mounted and unmounted horse blood lactate levels was only
found when the horses cantered. There might have shown no significance between the lactate
levels in the trot and walk because there was not a big enough difference in the mounted verses
unmounted weight, or the horses may not have been exercised long enough.
General Comments
Generally explain the paper’s strengths and weaknesses and whether they are serious, or important to our current
state of knowledge.
The project idea is well thought out, and well executed. There seems to be some information in
the introduction and discussion that is extraneous to the project. The paper overall seemed a bit
wordy, but very thorough.
The idea for the project is interesting. It’s relateableness to human physiology makes it
interesting. I don’t see what the importance of it really would be. I don’t think that they were
exploring a very new idea. Muscles get tired due to lactic-acid build-up. That is a known fact.
It seems like a lot of the references were used just for the sake of having lots of references.
Technical Criticism
Review technical issues, organization and clarity. Provide a table of typographical errors, grammatical errors, and
minor textual problems. It's not the reviewer's job to copy Edit the paper, mark the manuscript.
This paper was a final version
This paper was a rough draft
Unmounted is not a word (I looked it up just to be sure), but they use it about 50 times in their
paper. They have a few sentances which do not make sense.
The order in which they give information was good.
They forgot commas in most of their in-text citations, and put first initials before the last names
in all of their literature cited. They used and instead of & in their literature cited as well.
Most of the paper is in passive voice, but not quite all of it.
Most of the paper was justified, but not quite all of it.
Correction Key:
Delete
^insert
Sp., spelling