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Atkins for Equines?
Here's a deeper look at the role of carbohydrates in equine
feeds.
by
Ruth Bishop
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| Recently,
carbohydrate nutrition has come under an increasing spotlight.
Human health problems, such as type 2 diabetes, are linked to
serious consumption of "high carb" diets (combined
with little exercise). In a similar vein, the Atkins diet revolutionized
human weight loss programs with a central theme of amazing weight
loss on an exceedingly low carbohydrate intake, regardless of
the amount of exercise taken. As a result, this has brought
the issue of "carbs" right into focus: "high
carbs" are bad and "low carbs" are good. There
is even a "low carb" potato! (This is difficult as
potatoes are virtually all "carb"!).
"Low
carb" is now synonymous with a healthy lifestyle in humans,
and the focus has now turned as to whether "low carb"
can be good for horses as well. Whilst the term "low
carb" has yet to be absolutely characterized for horses,
this article will define carbohydrates, explain the benefits
of restricting intake of particular carbohydrates, and look
at the alternatives.
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What
is a "Carb"?
"Carb"
is short for carbohydrate, and there are two common forms
in our and our horses' diets: structural carbohydrates, derived
from fiber, and non-structural carbohydrates (NSC) from starch
and sugar.
Some
nutritionists claim low starch as meaning low carb, whilst
others cite "low carb" to mean low starch and sugar
or low NSC. These latter two are the more accurate definitions,
as a starch value alone does not give you, the horse owner,
a guide as to the sugar content. However, since the main non-structural
carbohydrate in equine compound feeds is starch, low starch
can be effective shorthand for a "low carb" or low
NSC feed, assuming it is not heavily molassed.
Horses are designed to eat diets rich in fiber (structural
carbohydrate), which is then digested by microbial fermentation
in the hindgut. This reflects the horse's evolution over millions
of years as a grazing herbivore, consuming a fiber-rich diet
of grass, shrubs and herbs.
Starch
and sugar (non-structural carbohydrates) are broken down by
enzymes in the small intestine. The end-products of digestion
(sugars) are rapidly available to the horse, and are often referred
to as quick release or "heating" type energy and have
been linked to why some horses become excitable on cereal-based
feeds.
Starch and Sugar Overload |
In their
natural environment, horses graze 16 - 18 hours per day, consuming
a fiber rich diet of grasses, shrubs and herbs, |
Given
that the relatively short small intestine is the only part of
the digestive tract where starch and sugar can be digested and
absorbed, any that passes through undigested ends up in the
hindgut. Here it will be broken down by microbial fermentation
and not by the horse's own enzymes. This fermentation produces
lactic acid, a strong acid that alters the gut environment making
it more acidic, which can kill the microbes present.
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Even
a partial starch or sugar overload can precipitate a disruption
to the hindgut fermentation, which can have a marked effect
since the hindgut comprises such a large part of the digestive
system.
Signs
of starch overload range from mild symptoms such as loose
droppings to the worst - colic, laminitis and exertional rhabdomyolysis
syndrome. (See Figure 3)
"Low
carb" diets (meaning low "non-structural" carbohydrate
(i.e. low NSC) in equine nutrition can avoid the negative
effects of starch overload. In addition to just avoiding starch
and sugar overload, low NSC diets can benefit young, growing
horses as well. New research has shown the source of energy
to be as important as the amount because the source directly
affects a hormonal cascade that directly influences the maturation
of bone. A growing body of evidence suggests that carbohydrate-rich
diets, such as traditional stud feeds, have a negative effect
on cartilage maturation and may play a significant role in
the development of certain developmental bone diseases.
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Figure 1: This diagram demonstrates the digestion
sites for the two types of carbohydrates in the horse's diet.
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What's
the Alternative?
If we wish to reduce the amount of starch and sugar the horse
is receiving, what are the alternatives?
1.
Dietary fiber (structural carbohydrates)
Dietary
fiber describes those carbohydrates that give "structure"
to plants or protective coats to seeds such as plant cell
walls and associated compounds. Fiber itself is made up of
different complex carbohydrates such as cellulose and the
hemicelluloses, which can only be digested using microbes
in the hindgut in a fermentation process.
The
horses' digestive tract has 65 percent of its volume dedicated
to the fermentation and absorption of nutrients from fiber
in the hindgut or large intestine. The end products of fermentation
are volatile fatty acids (VFAs), an important energy source
for the horse; a horse in light work will receive up to 75
percent of its energy requirements from VFAs.
As
the process of fiber digestion is relatively slow when compared
to non-structural carbohydrates such as sugars and starch,
it is often termed a "slow release energy" source
and therefore is less likely to cause excitability.
2. Fat
Fats and oils are concentrated sources of energy, containing
typically 2-3 times the energy content of the same weight
of cereal grains. Thus, they can be used effectively to replace
the energy from cereals when more calories are needed for
work or to maintain condition. Fat does not have the same
heating effect as cereals.
However,
remember that since fats are energy-rich, over-feeding them
leads to weight gain, as it does in all animals, and they
must be used with this in mind. Typically adding between 3
ounces to 1 pound per day is plenty for most working horses.
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When
to Feed Low Starch
Low starch feeds are effective for most classes of horses,
but here are a few specific cases where they can especially
provide great benefit:
1.
Perfect if your horse has a history of laminitis, tying up
or colic.
2. Indicated for young growing horses especially in the first
two years of life - high starch and sugar diets have been
implicated in the development of certain developmental bone
diseases.
3. Beneficial for horses that drop condition - these feeds
put weight and condition on without causing the horse to become
nervous or over-excitable.
4. Ideal for horses that need to work hard but calmly, such
as dressage horses
5. Excellent for horses that receive a lot of grain for work
- they will reap great benefits to health and performance.
6. Great for horses that need more energy than traditional
low energy feeds but become excitable when feed rates are
stepped up.
7. Useful for any horse in work - these feeds supply sustained
energy, appropriate for anything from trail riding to endurance.
8. Best choice of feed for horses on low or restricted forage
diets. Such situations occur if the horse has poor teeth,
if hay quality is poor, or of the horse is working hard on
large quantities of short feed.
9. High fiber compound feeds are excellent for horses that
have a dust allergy such as "Heaves" or Recurrent
Airway Obstruction (RAO) (formerly known as COPD)
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Typical
Starch & Sugar Content of Horse Feeds
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Laminitis
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| The
most common cause of nutritionally induced laminitis is
an overload of rapidly fermentable carbohydrate - either
from starch found in cereals and plants or sugars and
fructan found in grass. In addition to this direct effect,
recent research has suggested that the long term feeding
of sugar and starch based feeds may lead to changes in
glucose metabolism resulting in insulin resistance, which
has recently been identified as having a role in the development
of laminitis.
The
current advice on managing laminitis is to restrict
access to pasture at times of rapid grass growth and
avoid cereals and high cereal concentrates such as coarse
mixes (even "cool" mixes).
Alternatively
choose feeds based on fiber and fat with very low levels
of sugar and starch.
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Feeding
Strategies
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1.
Never feed more than 4 pounds of feed at one time (less
for ponies).
2. Keep starch intakes below 0.25 percent of bodyweight,
equivalent to 2 pounds of starch per meal.
3. Choose low carbohydrate (low starch and sugar) compound
feeds such as SPILLERS.
Starch contents below 20 percent reduce the likelihood
of starch overflow into the hindgut at typical feed rates.
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Ruth
Bishop is an equine nutritionist for SPILLERS horse
feeds in England and the author of the horse nutrition
bible.
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