On body weight loss in endurance horses:
Schott, et al, Pferdeheilkunde, July/August, 1996 (AESM proceedings)
In a 5-day, 424 km endurance competition:" Mean body weight decreased by 6.2,
3.2, 4.0, 3.3 and .9 % during days 1-5 respectively. Cumulative mean body
weight loss at the end of each day of the ride (in comparison to the pre-ride
value) was 6.2, 6.3, 7.4, 6.8 and 4.6% after days 1-5 respectively.
Persisting body weight losses (after overnight recovery) of 3.2, 3.5, 3.6,
3.7 and 4.1% after days 1-5 respectively, were not significantly different."
Thus, an 800 lb horse will lose about 50 lbs the first day, pay about half of
that back overnight, with the remaining weight loss persisting over the
entire event. What does the horse lose and pay back? Muscle fuel, water, and
electrolytes.
The study showing serum GAG depletion after competition was authored by
Calatroni, et al, and appeared in the same proceedings. The competition was
show jumping, not endurance. Some GAG components were reduced by 60% in this
study--others by only 20%.
The paper examining blood parameters of endurance horses, finding hydration
status, reflected in heartrate and respiration rate, as the key safety
parameter was written by Petr Jahn, et al, in the same proceedings.
In the same proceedings, Rivero found that endurance performance was
predicted by the ratio of type I to type IIA and IIB muscle fibers (high,
medium and low oxidative capacity, respectively). Those endurance horses with
higher oxidative capacities were the best performers..
In the same proceedings, Avellini et al studied diet and oxidative stress in
hard working horses and concluded, "The results obtained indicate that it is
necessary to test different diets during training, at least from the caloric
point of view. Such diets should also be enriched with substances which can
increase defences against free radicals."
Turner, same Proceedings, found infrared thermography "has been shown to be a
practical aid in the clinical evaluation of lameness...(and) can be used to
monitor the resolution of the inflammatory process."
Szarska, same proceedings, suggested the use of blood glucose determinations
as a health parameter during endurance rides. The investigator found
hypoglycemia in one of 23 horses at 80 km in a 120 km ride that also
demonstrated a lower resting hemoglobin before the start of the ride. This
failing horse was contrasxted with the best horse. After the race, glucose
recoveries were monitored. "After this type of exercise, a well-trained
organism is characterised by the phenomenon of supercompensation on the next
day after work. This was clearly visible in the case of the best horse. On
the next day after the ride the glucose level in the blood of the horse with
hypoglycemia was lower not only than its rest value but also than its level
from the recovery period."
Thus, a rapid blood glucose recovery in "the best" horse. Nonrecovery in the
poor performing horse that got in trouble at 80 km. It would appear that lack
of available substrate is a dangerous and harmful condition in an endurance
horse.
In Nutrition in Exercise and Sport (CRC Press, 1994, Wolinsky and Hickson
state, "If exercise is of sufficient duration and/or intensity (usually >2
hours), muscle glycogen becomes depleted, and muscles become reliant on blood
glucose for carbohydrate supply. Liver glycogen, gluconeogenesis (formation
of glucose by breakdown of amino acids) and exogenous dietary sources of
carbohydrate the maintain blood glucose levels as long as possible. When
blood glucose levels decrease below normal physiological levels, performance
deteriorates rapidly. Thus, maintenance of glucose supply to working muscles
should prolong performance and delay fatigue...The practice of glycogen
supercompensation, popularly known as carbohydrate loading, can produce
supranormal levels of muscle glycogen, which can lead to improved
performance, compared to a typical diet (cites 9 papers). Glycogen
supercompensation is designed for optimal performance during a single
endurance event, such as a trathlon, marathon, ultramarathon...any event
lasting over 90 minutes and leading to exhaustion signals a need for glycogen
supercompensation (four more cites)." The authors cite another ten papers
supporting carbohydrate feeding during endurance exercise.
In Equine Exercise Physiology 4 (ICEEP proceedings) Davie, et al, conclude
"The administration of large doses of dextrose i.v. after exercise increases
the rate of glycogen resynthesis.
Same proceedings, Valberg, et al, found that horses with a decreased ability
to store muscle glycogen showed poor performance and a "stiff, stilted gait"
following exercise.
Same publication, Farris, et al found "Glucose infusion increases maximal
duration of prolonged treadmill exercise in Standardbreds."
In Equine Exercise Physiology 3, Essen-Gustavsson et al said, "The results of
this study show that horses tolerate marked alterations in theirdiets without
any adverse effects" in a study (5 weeks) comparing high carbohydrate, high
fat and normal diets--no mention of tying up.
In the 1986 Equine Exercise Physiology 2 proceedings, Snow wrote the only
paper I can find by him concerning low, high and normal carbohydrate diets.
He states that after exercise, horses on high carbohydrate and normal
carbohydrate diets were 90% resupplied with glycogen within 28 hours, while
the low carbohydrate diet produced a 70% recovery in the same time period. No
mention of tying up.
The equine references provided here come from the four most important and
prestigious works produced over the past ten years in equine exercise
physiology. There were no pre-ex. glycogen loading studies among them and
there were no studies associating high carbohydrate diets, loaded or not,
with tying up. Dr. Snow was well-represented in all of them.
Susan, where are these glycogen loading/tying up studies you're talking about
in the exchange below?
> >and to avoid efforts at glycogen-loading per se, as
> > tying up has invariably been a factor time and again in research trials.>
> Is this published data? What was the loading/exercise protocol?
Of course it's published research. Protocol varied from project to
project as tying up was an unwanted nuisance variable, not the focus of
the study. Check your database, there's been alot of stuff in ENPS for
years and years.>>
I've checked several key references and found none--why don't you point the
way?
ti