Re: Matthew Mackay-Smith weighs in on carbs

[Mathew Pelletier <mathew@redhorsetech.com>]

Well Kat, I gotta hand it to you, your post stuffed my email box from
the good Ridecampers who I have been emailing with regarding the latest
and greatest in equine nutrition ;-).  I bet Susan's box is filled to
the brim!  Lots of us prefer to lurk, I guess.

Anyway, many of us do not subscribe to Trailblazer (and I never have
time to read it without sacrificing research papers), so forgive me if I
make an attempt to clear up the confusion a bit regarding carbohydrates
without referring to "x"'s article and so on.

Carbohydrates are in all plant material, whether it be pasture grass,
grain, or your favorite breakfast cereal.  There are differences in
carbohydrates which in turn, dictate how the horse will derive energy
from that feed source.  I will be explaining feeds in plant origin
versus animal based feeds, since I can't think of any horses from this
group that are fed tankage, lard, or enough Big Macs to constitute a
notable portion of their diet.

Soluable, or "nonstructural" carbohydrates are formed by chains of
simple sugars (glucose) linked to together by "alpha" bonds.  Amylase (a
digestive enzyme which is secreted into the small intestine primarily
from the pancreas) breaks these alpha bonds into a disaccharide
(maltose).  These disaccharides are then broken down into their
monosaccaride components by disaccharide enzymes.  These resulting
monosaccharides are absorbed and either used for energy, or when energy
needs are met, are believed to be stored as glycogen until those storage
areas are filled, then converted to and stored as fat.

Grains tend to have a considerable amount of these soluable
carbohydrates.  Their sugars are quickly absorbed through the small
intestine, thanks to the actions of various enzymes.  The fiberous
component of the grain continues its path to the cecum of the horse,
along with the the majority of carbohydrates in hay, grass, and other
"high fiber" feeds eaten by your horse.

The feeds that are high in fiber content are linked instead by beta
bonds.  No known enzymes can break these particular bonds, so the horse
must obtain energy from these particular carbohydrates in another way. 
Primarily, the cecum and colon are the "digestive factories" for these
carbohydrates.  The residing bacteria digest the fiber (breaking the
beta bonds) and in turn, produce volatile fatty acids (VFA).  The horse
can absorb the VFAs and use them as a source of energy.

Some fiber cannot be digested by the horse, such as lignin.  Lignin is
mostly found in the tree bark and fence rails your horse finds
entertaining to eat, hulls, and woody stems, just to name a few.

So, as a conclusion: Yes, your horse's ration contains a huge, massive,
absolutely obnoxious amount of carbohydrates, if he's eating any
digestible plant material (well, except that well-chewed fence rail in
the corral).  There is a difference in these carbohydrates, both in
their bonds and where/how they are digested, which helps to plague us
with the grain versus hay debate when feeding horses.


> p.s.  There is also and interesting article in _The Horse_ (July 1998) on
> "the latest" in feeding horses.  It had some recommendations for feeding
> young horses that I am NOT going to follow, but the article was
> interesting just the same.  Not the least of reasons being that the
> studies they used to determine the best way to feed young horses was based
> on the premise that optimal growth was the goal.  This is not MY objective
> when feeding youngsters.  Realize that many of the studies done on the
> "best way to feed horses" have very different goals than we have as
> endurance riders, and to date, there haven't been any real studies (otheer
> than the "one rat" variety that each of us does at home and at endurance
> rides) with these goals in mind (recognizing, of course, that not even all
> endurance riders have the same goals in feeding their horses).


Kat, I think the word "optimal" needs to be highlighted.  Optimal growth
is NOT "maximal" growth.  Forcing a horse to grow at maximum speed only
increases his chance of developing DOD (Developmental Orthopedic
Disease) and a whole host of other problems endurance horses (or any
horse, for that matter), does not need.  We should feed our endurance
prospects based on their particular needs (yes, every horse is an
individual), but to limit feed or nutrient haphazardly to "slow down
that growth" rate only leads to other, maybe more serious problems.

Dr. Ott (I'm assuming your talking about that article on page 55, which
I did make time to read :-)) was only explaining the considerations in
energy, essential amino acids, and protein that need to be made when
regulating the young horse's growth.  Many people are dumping every
mineral/vitamin on the market at their young horses to prevent such
things as DOD, but have not even taken a second to consider the amount
of energy or type of protein they are feeding to their horse.  Too much
energy, as well as deficits in a few minerals such as copper and zinc in
relation to that amount of growth, can cause DOD (references available
upon request).

I don't think "potential" endurance horses should have their growth rate
reduced from optimum because of a "scare" of developing DOD.  You do
WANT to prevent a "maximum" growth rate, and growth rates that fluctuate
wildly.  There is a definite line there.  Understandably, if the young
horse is out of/by a parent who has a genetic disposition for DOD, the
growth rate should be carefully monitored.  But endurance breeders
should not be producing foals out of that stock anyway... just ask my
mare.  She has DOD (genetic) and may have been a pretty good endurance
horse, but that's all shot to oblivion.  I will never breed her, ever. 
So, Kimmy doesn't have a horse to ride any endurance rides with right
now.  Everyone should keep in mind that when a person takes the
inititive to produce a foal destined for a long, useful life, one must
also take the responsibility to use common sense when feeding and caring
for the foal's health.

Threw in my two cents (and maybe more ;-)) worth... anyone awake???

Kim 

(PS, any email received after Friday night cannot be read until ???, as
we're moving on Saturday to Texas (look out, folks!).