Tom Ivers seems to be advocating feeding grain sooner before the start of
the ride. Conventional endurace wisdom (AERC handbook, Dr Loving's Go
the Distance book) says grain should be fed at least 4 hours before the
start of a ride. From the previous posts, grain gives a spike in glucose
about 2 hours after feeding and then insulin increases and moves the
glucose to the muscle cells as glycogen. Glycogen is an ideal muscle
fuel. So it seems to be me like it would be ideal to feed grain 4
hours before a ride so that it is already processed into glycogen
before you start.
Now as to grain during the ride. Dr. Loving's book recommends no more
than 2 pounds at each vet check. The AERC handbook states that a horse
doing a 100 miles will burn more calories than are found in 50 lbs of
corn. (Most of us are only doing 50 miles but who thinks a horse can
eat 25 lbs of grain during a ride?) This means that your horse is
going to have to burn body fat during an event. I believe that one
purpose of long slow distance work is to train your horse's body to do
this; certainly this has a parallel in human physiology. Since it
is important to keep your horse's guts working you want him to eat some
water holding fiber at the vet checks. So you should certainly limit
grain to a small enough portion that your horse will also eat some hay
&/or beet pulp or bran.
If, like me, you are riding to complete not win while you build your
horses "base" and your own experience it is probably safest to feed
your grain the night before and limit grain at vet checks even more.
This is easy for me, because Grey prefers hay or grass to grain at
holds. I have been feeding him his grain just 2 or 3 hourse before the
ride this year and he has not had great gut sounds or hydration factors.
Next year I am going to try graining the night before the ride
instead of that morning. If at some point in the future, I am going
for faster rides then I will try some of the carbo loading techniques,
and give him grain 4 hours before the start of the ride, but that wont
come until we both have a lot more experience. At this point keeping
him hydrated is way, way more important than worrying about fueling
him for maximal performance.
Just my .02 worth,