Re: Carbs - only part of the picture

[Tivers@aol.com]

In keeping with the "30 years of equine nutritional science" theme, we move
forward from Lon Lewis' 1981 book to two papers in Equine Exercise Physiology
II, published in 1987.

Meyer, et al studied military horses performing exercise similar to that of
endurance horses. He suggested a diet of 10 kg/day concentrates and 5.6 kg/day
hay. He said, "The energy requirements on days with hard exercise cannot be
covered by feed intake. Horses doing strenuous exercise have to mobilize
energy, particularly from the fat stores of the body. Before starting a long
distance ride, the horse should gain fat and increase its weight."

Pagan, et al  fed horses three diets that included haylage at 30% of total
igestible energy, a control diet consisting of 39.9% starch, a high protein
(24.6%) diet with 24.2% starch and a high fat (18%) diet containing 30.8%
starch.  In an endurance type of exercise lasting 110 minutes, muscle glycogen
dropped from 680 to 580 mmol/kg with the control diet. With the high protein
diet, muscle glycoen was lower to begin with (580 mmol.kg) and dropped to
about 450 mmol.kg during the work. In the high fat diet, muscle glycogen
dropped from a high of 580 mmol/kg to a low of 430 mmol/kg.  "The results of
this study clearly indicae that the proportions of energy generated from fat
and carbohydrate can be altered in exercising horses through dietary
manipulation."

Snow, et al, studied glycogen repletion after a treadmill exercise that
depleted muscle glycogen stores by 40%. Snow: "Endurance capacity in man at
work intensities of 60-85% of VO2max is directly related to the content of
glycogen in the working muscles. Prolonged exercise may result in almost total
depletion of glycogen in the muscle fiber bed" (citing himself). Snow's
experimental "normal" diet included 9kg/day concentrate and 4.5kg/day hay. In
his "high carbohydrate diet he added .45 kg of glucose IV. In his low
carbohydrate diet he fed 5.5 kg hay and 3.6 kg concentrate. Glycogen depletion
during the exercise was less in the normal and high carb diets and both
outperformed the low carb diet during the recovery process. Snow: "The faster
rates of glycogen repletion during the first 28 hours with the normal and high
carbohydrate dits, compared to the low carbohydrae diet, is not surprising in
view of the many studies in man of the effects of supplemental carbohydrate."

Unlike Sarah and Heidi, Snow seems to give some credence to human studies.
Remarkable. Anyway, perhaps in the past decade a complete revolution in
feeding athletic horses has occurred. So far, no 40lb/day hay diets have been
encountered. And nobody seems to be overly concerned about manipulating the
contribution of FFAs from the hind gut in order to produce performance or
recovery  improvements.  So, in at least 20 of the past 30 years of equine
nutritional research, there is no sign of whopping benefits from low carb,
high hay diets. No glycogen sparing. No increased endurance. And no researcher
has even suggested a "normal" diet for performance horses that contained much
less than 50% concentrate. 

Well, let's move onward toward modern times-and as we do, remember the changes
in educational philosophy  that have taken place from the late 70's on. We're
quickly coming to the point where everyone with an opinion, or an
extrapolation of limited fact, especially those with  initials following his
or her name, will be considered to be telling Truth, relativistic and
subjective as it may be.  

Rolling right on into 1991 with the publication of Equine Exercise Physiology
3 and here's Rodiek, et al looking at corn vs alfalfa pre-feeds before an
hour's worth of exercise. "Within 30 minutes of the exercise being completed,
the glucose levels in the alfalfa fed horses had returned to values not
greater than pre-feeding. In the corn fed horses, however, glucose
concentration remained elevated above pre-feeding for two hours." "The dietary
effects on the post-exercise glucose rebound are not entirely clear. Hepatic
glucose production in the corn fed horses may have been greater thatn in the
alfalfa fed horses due to higher blood glucose levels and presumably larger
glucose deposition into the liver prior to exercise." 

P. Miller, et all studied excess protein feeding and found deleterous effects
with too much protein. The control diet contained 29.7% corn starch while the
high protein diet contained none. The higher protein (moving from 9% in the
control diet to 18.5% in the high protein diet) was achieved by nearly
tripling the intake of hay and soybean meal  while eliminating the cornstarch.

Essen-Gustavsson, et al, compared a normal diet (6kg/day timothy hay and
3kg/day pelleted concentrate-1680g/day carbohydrate, 216 g/day fat, 579 g/day
protein) with a high fat diet (1203 g carbs, 531g fat, 585 g protein) and a
high carbohydrate diet (2037g carbs, 168 g fat, 591g protein). Investigation
took place over 5 weeks. With the exercise test that followed, "V200 was lower
in the CHO diet and Vla4 was lower in both fat and CHO diets compared to the
normal diet." Time to fatigue did not vary with diet (these diets were
delivering equal energy of about 89 MJ). "In conclusion, the results of the
present study indicate that exercise time to fatigue during submaximal
trotting on a treadmill for approximately one hour is not influenced by the
different diets employed." Again, with energy levels held constant across
diets.


Welp, still trying to find a study using 40 lbs of hay (or anything close) and
almost no grain with endurance exercise. So far, no luck. This feeding
revolution must have occurred in the last 7 years of our 30 year quest for
equine nutritional knowledge. Maybe in Equine Exercise Physiology 4, 1995:

Pagan, et al, finds fat feeding "safe" using a 12% fat supplemented diet.
Control group got grass hay and fortified sweet feed in roughly equal amounts
and a pellet was added for the increase in fat.

Hughes and Potter, et al, crow about getting higher pre-ex muscle glycogen in
Quarterhorses fed 10% fat short term. Equal amounts of hay and grain. 

Eaton, et al achieve improvements in performance with short-term 12% fat
feeding in high intensity exercise.

Farris, et al, find that glucose infusion increases maximal duration of
prolonged treadmill exercise. For those of you in Rio Linda, glucose is
carbohydrate.

Carolyn Stull, et al, found: "Lipids in the form of FFA are an important
source of energy for submaximal exercise in the horse. The primary source of
circulating FFA is from lipolysis in the adipose tissue and secondly from the
triglyceride depots within the muscle". The researchers found that feeding an
alfalfa meal or a corn meal before exercise altered the percentages of the
type of fuel (fat/glucose) mobilized to carry out the exercise. The horses fed
nothing had the highest FFA mobilization during the exercise, alfalfa fed
horses the next highest FFA mobilization and corn fed the lowest FFA
mobilization. So, if Free Fatty Acid mobilization is the goal, starving the
horse is the solution.

McMenimen finds no difference in performance using different grain types or
vitamin mixes in stockhorses.

Whoops! Here we are! Here we are!  Danielsen, et al, studied roughage in
endurance horses for its effect on electrolytes and water balance--and found
"The increased water intake and lower plasma protein concentration associated
with the hay diet may be beneficial for horses involved in endurance type
exercise. 

The exercise test consisted of 6 15 minute bouts at 4 meters/second and 7m/s.
the diets tested were, Hay, 7.3kg the night before and Limited Hay, 1.8 kg
concentrate and 2.3kg hay the night before. During the exercise, heartrates
were higher in the Hay diet, and at 15 minute intervals after the exercise,
the heartrates for the Hay diet remained higher than the Limited diet--at 15
minutes the heartrates were 116 (H) and 115 (L) and at 75 minutes they were
115 (H) and 110 (L). There was more water loss in the H diet though the work
and recovery periods. The rectal temps of the H diet horses were about even
during the exercise and immediately after, but at 2 hours the H diet horses
were at 38.5 while the L horses were at 38.1. Diet did not affect weight loss
(4%) during exercise. Due to a higher Total Protein after the L diet, the
authors concluded that the hay diet was beneficial. 

So, if higher body temps and heartrates are your goal, along with lower Total
Protein levels, go with hay. 

More from EEP-4:

Mueller, et al, found that "Long term undernutrition in donkeys leads to
decreased carbohydrate reserves, diminished maximal aerobic capacity and
endocrine alterations. Work difficulty and stress level may increase, with
possible negative implications for animal health and endurance."


Well, we've made it to 1995 and have only one paper so far that used hay
exclusively, overnight, as a setup for a semi-endurance exercise test. I
didn't like the looks of the results.  Of course, the hay was only 14 lbs, not
40 lbs, so maybe there's a huge advantage to be found with that approach. 

Stay tuned. Still looking.

ti