> However, I don't have available right here any citations that document
> what expected glucose levels would be in a horse being fed hay vs. a
> fasted horse. If anyone has those numbers available, maybe they could
> post them to the list for this discussion.
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Research from: Responses of Blood Glucose, Insulin and Cortisol
Concentrations to Common Equine Diets (CL Stull, AV Rodiek. Journal of
Nutrition, V118:206-213, 1988):
Four 2 year old QH gelding were used in two experiments (Latin Square
design):
Experiment 1: Fast the horses for 38 hours, and no samples were taken
for the first 14 hours. After 14 hours of fasting, blood samples were
taken every 15 minutes through a 10 hour period, then samples were taken
one an hour for the remaining 14 hours of the fast.
Experiment 2: Four feed trials were preformed on these same horses.
Each was fed chopped oat/alfalfa hay for maintenance, and a trial's
ration which comprised 25% of the horse's daily digestible energy (DE)
requirement. One ration was 100% alfalfa (diet A), another was 50%
alfalfa/ 50% corn (diet B), diet C comprised of 100% corn, and diet CO
was 90% corn and 10% corn oil; all were measured to provide 25% of the
horse's DE requirements. Water was provided ad libitum (always
available), and a week was provided between trials.
In experiment 1 (fasted horses), the glucose levels ranged between 90
mg/dl to 108 mg/dl, with the mean around 96 mg/dl for the first 10 hours
of sampling, and mean of 102 mg/dl for the last 14 hours of sampling.
Please keep in mind that I am not a statistician, but any really unusual
peaks did not exist on the graphed data. Insulin levels ranged between
2.5 microU/ml and 11.0 microU/ml.
With experiment 2, glucose and insulin levels began to rise within one
hour after being fed, on the average.
The 50% alfalfa/ 50% corn diet (AC) demonstrated the highest climb of
all of the rations... 2 hours after beginning to eat, the glucose levels
were 143 mg/dl and insulin was 50 microU/ml (after 2.5 hours). These
peaks lowered back to "baseline" within 4 to 5 hours after being fed
(glucose within 4, insulin with 5 hours).
The 100% corn diet (C) followed with the next highest climb: glucose
peaked at 142 mg/dl two hours after being fed, and insulin peaked at 30
microU/ml one and a half hours after tossing food at 'em. The glucose
peak dropped to "baseline" after 5 hours from initial feeding, and
insulin levels followed suit. What was interesting to note was that the
elevated insulin levels "hung" for a about three hours after initial
feeding, while the AC diet followed a nice hyperbolic-type curve.
The 90% corn/ 10% corn oil diet (CO) peaked at 115 mg/dl one and a half
hours from initial feeding, and insulin peaked at 18 microU/ml at about
the same time. Peaks dropped to "baseline" after 3 hours from being
fed. Really interesting response was found too, maybe from the corn
oil: a second peak in insulin was found after 7.5 hours from initial
feeding (20 microU/ml), while all of the other diets were still falling
in their insulin levels. The glucose level did not peak with insulin in
this second response, though.
The A diet (100% alfalfa) had the smallest peak of all of the rations.
The glucose peak barely existed (102 mg/dl after 1.5 hours) and insulin
didn't peak at all worth mentioning.
I'm considering "baseline" to be between 90 and 100 mg/dl for glucose,
and 4 to 8 microU/ml for insulin.
In summary, if you want the lowest glucose/insulin peaks, feed high
fiber/ low starch feeds to maintain blood levels. Susan mentioned the
differences of equine digestion in a past post which explains why this
would occur, so I won't re-tell the story. For the lowest peaks, feed
nothing at all, but using common sense, you really don't want to run 50
miles or more on an empty stomach, do 'ya? Your horse wouldn't want to
either.
For the "racehorse" peaks that Tom wants, it looks like the corn or
alfalfa/corn ration was the best choice (the C diet peaked a little
faster than AC, but AC hung around a little longer with a more gradual
slope). A full gut of forage would be detrimental for optimal
preformance in racing such a short distance, compared to endurance.
Kim (and the forage-munching 'Lee)