Download Equine Digestion - Merrick`s, Inc.

Equine Digestion
Developed by
Rob Costello, Technical Specialist
MERRICK’S, INC.
A Subsidiary of Merrick Animal Nutrition
P.O. Box 620307 • Middleton, WI 53562-0307 USA
800-MER-RICK (637-7425)
www.merricks.com
© Merrick’s, Inc. 2012
Equine Digestion
Horses are classified as herbivores, or roughage eaters. They are grazing animals with digestive systems
designed for constant consumption of plant food.
Unlike most other herbivores, the digestive system of
the horse is considered monogastric rather than ruminant. Digestive organs include the stomach, small
intestine and large intestine. The stomach and small
intestine are commonly referred to as the upper gut,
and are where most of the protein, fat, vitamins and
minerals contained in feed are digested and absorbed.
Although the horse lacks the complex forestomach of
a ruminant, unique characteristics of its large intestine, or hindgut, allow the horse to utilize cellulose
and other fermentable substrates in much the same
way as ruminants.
The large intestine of the horse has a greatly enlarged
cecum which serves as a fermentation vat. Billions of
bacteria and protozoa produce enzymes that break
down plant fiber, In the horse, this fermentation process occurs posterior to the area where most nutrients
are absorbed, and as a result, horses do not obtain all
of the nutrients sysnthesized by microorganisms in the
large intestine.
The Stomach
After feed particle size is reduced through chewing
and feed is mixed with saliva in the mouth, it moves
down the esophagus and into the stomach. The
stomach stores, mixes digests and propels feed into
the small intestine. Very little of the feed nutrients are
absorbed in the stomach. Proteins and carbohydrates
are only partially digested in the stomach, and fats are
only slightly hydrolyzed before the food passes into
the intestine.
©Merrick’s Inc., 2012 Equine Digestion
1
The stomach of the horse contains about 10% of the
capacity of the intestinal tract compared to about
70% for ruminants. This means the horse’s stomach
has only 14% the capacity for feed as the mature
ruminant and cannot handle large amounts of feed
at one time. One the other hand, if the stomach
remains empty, the excess gas produced can cause
the stomach to rupture, leading to death. Therefore,
the horse must eat frequent small proteins of feed
to avoid overeating and possible injury from colic,
founder, or damage to the stomach.
Once in the horse’s stomach, feed passes rapidly
into the small intestine. Feeding a large meal limits
the mixing action of the stomach and may prevent
feed from coming into sufficient contact with gastric
secretions in the stomach. This can have a negative
effect on feed digestion.
The Small Intestine
The small intestine contains about 30% of the
total weight of the digestive tract of the horse, and
is where most feed nutrients are digested and absorbed. The horse’s digestive system is designed so
that soluble carbohydrates and proteins from grains
are digested and absorbed in the upper gut. The
small intestine of the horse also serves as a conduit
for moving a large amount of undigested insoluble
carbohydrates from forages into the large intestine.
The rate of passage of feed through the stomach and
small intestine is very rapid. Grinding or chopping
feed increases the rate of passage and decreases absorption of nutrients. Since the upper gut comprises
only 40% of the digestive tract and feed moves
through rapidly, it is relatively easy to overwhelm
the digestive capacity of the stomach and small
intestine. If large amounts of soluble carbohydrates
reach the large intestine, they will be quickly fermented. This may result in excessive gas and lactic
acid production, leading to colic or founder. To
avoid the potentially damaging effects of overeating,
horses should be fed small amounts 2 to 4 times a
day depending on the horse’s activity or use level.
2
The Large Intestine (hindgut)
The horse has the largest and most complex large
intestine of any domestic animal. Its large intestine
is made up of two large organs: the cecum and the
colon. Together they represent about 60% of the
horse’s digestive tract. The cecum makes up about
25-30% of the large intestine.
The horse’s large intestine is designed to utilize plant
fiber. Insoluble carbohydrates such as cellulose and
hemicellulose from forages, as well as starch and
other soluble carbohydrates that were not digested
in the small intestine, flow into the large intestine.
As Feed leaves the small intestine it first enters the
cecum. Here the undigested nutrients are fermented
in a process similar to that which occurs in the
forestomach of ruminants. After fermentation, feed
enters the colon for further digestion and absorption. Microbial fermentation in the hindgut results
in the production of volatile fatty acids which are an
important nutrient source for the horse. The hindgut also serves as reservoir of water and electrolytes
which are vital to sustain exercise performance.
The rate of feed movement through the colon is
relatively slow. Because the colon folds back on
itself several times and its diameter varies, horses are
predisposed to digestive upsets when nutrient flow is
abnormal. Since the horse’s digestive tract is primarily designed to digest forages, fewer problems occur
when the diet is predominately hay or pasture.
Colic
The horse’s digestive system is susceptible to impaction, twisting and other types of colic. Colic can
result from the formation of gaseous products derived from microbial fermentation. If large amounts
of soluble carbohydrates, such as starch, reach the
microorganisms in the hindgut, large amounts of
gaseous compounds are produced. Since these gases
are being produced faster than they can be absorbed
or released, swelling occurs. This swelling can, and
often does, cause the horse to develop colic.
©Merrick’s Inc., 2012 Equine Digestion
Nutrient Requirements
Good Management Practices
With its small, simple stomach and large fiberdigesting hindgut, the horse is designed to eat small
portions in a continuous fashion. By design, forages
should predominate the horse’s diet. Grain, fat, supplemental protein, vitamins and minerals are important, but should make up a smaller portion of the diet.
1. Provide plenty of clean, fresh water. A horse will
drink between 2 to 4 lbs of water for each pound of
ration consumed.
Mature horses consume about 2.5 to 3.0% of their
body weight in feed each day. A mature 1000 lb horse
will eat about 25 to 30 pounds of feed each day.
Ideally, horses should consume a minimum of 1%
of their body weight in hay or pasture each day. As a
general rule, forages should comprise at least 1/2 of
the total weight of daily feed consumption for optimum growth and development.
A horse’s nutrient requirement varies depending on
its activity and function. Generally, nutrient requirements are presented according to the following classifications: maintenance, work, growth, gestation and
lactation.
A maintenance ration allows a mature, idle horse to
maintain its weight and body condition under average climate conditions. Nonworking adult horses
can be maintained on high quality forages without
grain supplementation. However, the horse’s requirement for energy increases 25%, 50% and 100% as its
work level increases from light, to moderate, to heavy.
Growing, breeding, working and performance horses
require grain or concentrate supplementation to meet
their additional nutrient requirements.
During the last three months of gestation, a mare’s requirement for protein, minerals and vitamins increases. As pregnancy moves through the ninth, tenth and
eleventh month, the mare’s need for energy increases
11%, 13% and 20%, respectively. Lactation also
means additional requirements for protein, minerals
and vitamins.
Stress associated with a horse’s environment may also
affect its nutrient requirements. Changes in temperature, moisture and humidity as well as muddy lots
with little or no housing are a few examples of situations that can lead to stress. These and other factors
can alter the horse’s need for various nutrients
2. Ensure your horse has enough feed to eat.
3. Feed all feeds by weight, not by volume.
4. Have the hay analyzed and develop the rest of the
diet bases on the forage quality. If this is not possible,
feed hay that smells clean, has fine stems, lots of leaves
with minimal seed heads or blossoms and is not damp
or weedy.
5. Feed at least 1 to 5 lbs of forage for each 100 lbs of
body weight. Total daily feed should be about 2.5 to
3.0 lbs per 100 lbs of body weight.
6. Avoid dusty and moldy hays and grains. Dusts and
molds can lead to indigestion and respiratory diseases.
7. When needed, feed concentrates at least twice daily.
8. Use top quality feeds and choose rations that are
balanced to your horse’s nutrient requirements.
9. Feed horsed individually if possible to prevent aggressive horses from overeating and submissive horses
from undereating.
10. Feed at regular time intervals and make major
changes in the ration gradually over several days. Do
not increase grain feeding faster than 1/2 lb per day.
11. Allow horses one hour after feeding to digest the
meal before forced exercise.
12. Allow a hot horse to drink frequent small amounts
of water after exercise. Never give grain to water to a
hot horse in large quantities.
13. Watch your horse closely as it eats for changes in
appetite. Sudden changes alert yo to potential health
of feed problems.
14. Avoid overfeeding.
©Merrick’s Inc., 2012 Equine Digestion
3