Nutrition
for Maximum Performance
By Eleanor Blazer
LESSON
ONE
UNDERSTANDING THE EQUINE DIGESTIVE SYSTEM
The equine digestive system is like a disassembly
plant. It takes water and feed (forage, concentrates
and supplements) and breaks them down into a form the body can utilize.
There are two methods of processing:
mechanical and chemical. The organs that
make up the digestive tract do the processing.
Mechanical processing starts in the
horse’s mouth as he uses his lips to sort and choose the desired feed. While grazing he will use his incisor teeth
to bite off the grass. The tongue then
moves the material back to the molar teeth where it is chewed and
swallowed. The stomach continues to
break down food with a churning action.
Chemical processing is present through
out the digestive tract. It starts with
the saliva in the horse’s mouth and ends in the large intestine. Bacteria, enzymes, and other substances are
used to release the nutrients needed by the horse.
Horses are non-ruminant herbivores –
they eat plants, but do not have a rumen.
Animals with a rumen (cows, sheep, and goats) swallow the feed directly
into a fermentation vat, the rumen, where it is broken down by bacteria. It is then regurgitated and chewed again
before being re-swallowed. But, horses
are hindgut fermenters. The feed a horse
eats goes through the chemical and enzyme process before it is fermented in the
hindgut. Horses do not chew a cud.
Notice,
in the diagrams below, the horse’s meal enters the stomach; while the cow’s
meal enters the rumen. Also notice how large the equine cecum is when compared
to the equine stomach.
THE
EQUINE DIGESTIVE SYSTEM
THE
BOVINE DIGESTIVE SYSTEM
The best way to learn about the equine
digestive system is to follow a meal, as it is broke down and processed. Please refer to the equine digestive system
diagram as you follow the path.
LIPS
Equine
lips are very sensitive. Any horse owner
who has tried to add medication, dewormer or a
non-palatable supplement to grain can attest to the dexterity of the upper
equine lip. This “prehensile” ability
allows horses to grasp the most succulent grass. It also aids them in the ability to open
stall latches, untie ropes and perform other feats of amazement.
SALIVA
Once the horse has gathered the food
into his mouth he begins to chew. The chewing
action stimulates three pairs of salivary glands – (1) the parotid, (2) the
sublingual and (3) the submaxillary/mandibullar. A horse will produce 5 to 10 gallons of
saliva per day.
If a horse does not get enough
chew-time the feed is not moistened sufficiently. Senior horses or horses that bolt their feed
can have problems with the feed causing an obstruction in the esophagus
(choke).
Saliva
also helps buffer the acids in the stomach.
This helps protect horses from getting ulcers. The more forage a horse receives, the more
saliva produced and the more buffering within the stomach.
TEETH
The teeth are very important to the
health of the horse. Many nutrition
problems start here, so an understanding of the healthy equine mouth is
important.
By the time a foal is a week old he
will have 4 incisor teeth – 2 on the top and 2 on the bottom, these will be in
the center. In another week the second
set of incisors will come in and by 6 months of age the corner incisors will be
in. Also, the pre-molars will be coming
in at about the age of 2 weeks. There
will be 6 pre-molars top and bottom. So, by the time the foal is 6 months of
age he will have all his baby teeth, a total of 24 teeth.
The baby teeth, or caps, will start to
shed by the age of 2 ½ years. The
erupting permanent teeth will shove the caps out of the way. You may find them in the feed box. There are times when the caps will not be
pushed out and this can lead to problems.
An equine dentist or veterinarian will need to remove the cap, so the
permanent tooth will come in properly.
Most adult mares will have 36 teeth
and males can have 38 to 40. The extra
teeth males have are called canine teeth.
Mares do not usually get them and if they do they will be very
small. Canine teeth will not erupt until
4 to 5 years of age.
A type of tooth that may cause
problems is a wolf tooth. They are found
in front of the molars. Wolf teeth do
not serve any purpose. They may interfere
with the bit. Many equine dentists and
veterinarians re-commend they be removed.
They have short roots and are easily extracted. Wolf teeth usually erupt between the age of
12 and 18 months.
The upper jaw is wider than the lower
jaw and at rest the back teeth do not meet.
As a horse chews his lower jaw moves side to side and this action causes
the teeth to grind together. This
grinding action causes the teeth to wear away.
Below the surface of the gum-line is almost 4 inches of tooth, which
erupts continuously as the exposed surface wears away. So, by the time a horse is in his twenties
the amount of tooth left to erupt is a lot less than a horse that is 4 years
old.
In
this diagram of a fairly young but mature horse, notice how much tooth is below
the gum-line.
Routine dental examination is
important to how well a horse will utilize his feed. If all works well the teeth will wear away
evenly, but that is rarely the case.
Malocclusion, a term used to describe when teeth do not meet properly,
can occur.
Overtime, points (sharp edges) can
develop on the inside of the lower teeth and the outside of the upper
teeth. These sharp edges inhibit the
side-to-side movement of 
the lower jaw and soon the horse
has lost the full range of the chewing action.
These points are also very sharp and can lacerate the inside of the
mouth and side of the tongue. Horses
will pack material between the teeth and cheek to try to pad the sore
area. An equine dentist or veterinarian
will “float” or file off these points.
This procedure does not hurt, because the adult equine tooth does not
have nerves or blood supply.
A missing tooth can also cause
problems. The corresponding tooth
continues to erupt, but is not being wore off. Soon it is sticking above the
rest of the arcade of teeth and the horse cannot chew properly. This tooth will
need to be filed on a regular basis to prevent malocclusion.
The type of feed the horse eats will
also affect the wear of his teeth. A
horse that has a diet of only pellets or complete feed without any long stem
fiber will have uneven wear of teeth. A
horse that eats this type of diet or only hay will also develop long
incisors. Because he is not nipping
grass off with his incisors they can become long, which prevents the molars
from grinding the feed properly.
Malocclusion can also be a genetic
problem. Horses with inherited tooth
problems will need to be monitored regularly and offered feed they can utilize.
Once the food has been chewed and
softened with saliva the horse swallows.
ESOPHAGUS
The esophagus is a muscular tube that leads to the
stomach. The length is about 50 inches
for an average sized horse. It lies
along the left side of the neck, just below the trachea (windpipe).
Choke, an obstruction of the
esophagus, is a feed related concern. A
horse that bolts (eats feed too quickly) his grain or does not have enough
saliva to soften the feed can get the dry material stuck in his esophagus. Also, a horse that has tried to swallow a
corncob or other large object can develop this problem. As the horse continues to eat the feed cannot
pass by the obstruction and the material builds up in the esophageal tube.
The symptoms of a horse choking are
frequent attempts to swallow, stretching out of the neck, excessive salivation,
and feed material mixed with saliva coming out of the nose. A veterinarian should be called immediately
as severe damage to the esophagus can result.
Unlike humans, horses can still breathe while choking, but immediate
care is still needed.
Choke can be avoided. A horse that bolts
his feed should have several large rocks placed in his feeder. He will need to
move them around to eat his ration. A horse that has an inflamed esophagus or
does not have enough moisture to break down the feed should be provided with a
feed that can be pre-soaked. This will
aid in the passage of the feed to the stomach.
Soaking the feed should also be done for seniors or horses that have
tooth problems which result in them not being able to chew properly. Avoid feeding horses large pieces of apples,
carrots, cubes, and treats.
A unique feature of the equine
esophagus is the very strong cardiac sphincter valve. This valve is located where the esophagus
joins the stomach and prevents food from being regurgitated. It also prevents
horses from burping. The horse’s stomach
will usually rupture before this valve allows the material to be
regurgitated. This results in death and
is why feed must be of the quality and quantity the horse can handle.
STOMACH
The stomach of the horse is very small
in relationship to the size of the horse.
It only makes up 8-10% of the capacity of the digestive system. The average horse’s stomach will only hold
about 2 - 4 gallons and is about the size of a football. The stomach breaks food down mechanically
and chemically.
The
equine stomach is divided into two basic sections: the saccus
cecus (nonglandular
squamous mucosa) and a glandular section.
There is a distinct ridge which divides them called the margo plicatus.
The
nonglandular section is not protected from acid
produced by the lower glandular section.
This area is prone to ulcers. The
pH level in the saccus cecus
is approximately six (6) to seven (7).
Within
the glandular section are two acid production regions – the fundic region and
the pyloric region. This area is
protected from acid by a mucous membrane.
The
fundic section produces pepsin enzymes, gastric lipase enzymes, and
hydrochloric acid which break down feed.
Most of the digestion takes place in the fundic section. Pepsin breaks down protein into amino acids,
which can then be utilized by the horse.
The feed is also mixed with hydrochloric acid and bacteria that produces
lactic acid. The pH level in the fundic
sections is approximately five (5).
The
pyloric section produces a small amount of enzymes and mucus. The pH level in this section is about two (2)
– it is highly acidic.
The
stomach does not break down fiber, so very little forage is digested in the
stomach.
But
fiber/forage is still needed to buffer the acids within the stomach. Forage also keeps the acids within the
glandular section from “sloshing” up into the unprotected nonglandular
section during exercise.
The muscles in the stomach uses
rhythmic contractions called peristalsis.
This mechanical action helps break down feed into smaller particles.
The design of the equine stomach is
such that a horse needs small frequent meals.
It fills quickly and empties quickly.
Feed usually only remains in the stomach for about 20 minutes. Ulcers can result if the stomach is allowed
to become empty.
Feeding a horse too much grain at one
feeding causes the excess to be pushed into the small intestine before the
digestive juices have a chance to break it down. Colic will be the result.
The pyloric sphincter is located where
the stomach joins the small intestine.
Once the meal is broken down the valve relaxes and the feed passes
through to the small intestine.
SMALL
INTESTINE
The small intestine is a tube that measures about 50
- 70 feet in an average sized horse. Its
capacity is approximately 15 gallons.
Most of the nutrients from the grain portion of the diet are absorbed in
the small intestine.
The breakdown of these nutrients
relies on chemicals secreted by the pancreas, liver, and intestinal
mucosa. Pancreatic enzymes help digest
the feed. Because the horse has no
gallbladder, bile is constantly flowing in from the liver. Bile breaks down fat. The available nutrients are then absorbed
through the walls of the intestines.
Feed passes very quickly through the
small intestine. In as little as an hour
some types of feed will have moved through.
However, it usually takes up to 8 hours for most of the feed to reach
the end of the small intestine. It is
very important to the health of the horse that soluble carbohydrates are
absorbed in the small intestine. If they
reach the large intestine fermentation can occur which will result in gas and
colic. To avoid overloading the small
intestine small frequent meals are strongly recommended.
Starch, complex sugars, protein from
the grain portion of the diet, fat, fat-soluble vitamins (A, D, and E), and
most minerals are absorbed in the small intestine. Protein from roughage, fiber, and phosphorus
is not digested well in the small intestine.
The small intestine consists of three
sections: the duodenum, the jejunum, and the ileum.
The duodenum prepares the food for absorption
by mixing it with enzymes and chemicals. Very little of the nutrients are
utilized here.
The jejunum is the longest portion of
the small intestine. Most of the
nutrients from the grain part of the diet are absorbed in the jejunum. Lining the inside of the intestinal wall are
tiny projections called villi. The villi
absorb the nutrients, which are now molecules and allow them to be utilized by
the horse.
The ileum is the last section of the
small intestine. The absorption of water
and water-soluble vitamins takes place here.
The insoluble carbohydrates (fiber),
any starch, or other material that was not utilized in the small intestine now
moves on to the large intestine.
LARGE
INTESTINE
The large intestine is 25 to 30 feet
long in an average sized horse. It has
the largest capacity of the equine digestive system at approximately 30
gallons. Feed will remain in the large
intestine for about 48 to 65 hours.
(Notice
the large intestine is shorter in length than the small intestine, but holds
twice as much.)
Digestion of insoluble carbohydrates
takes place in the large intestine.
Protein from the fiber portion of the diet is utilized. Phosphorus is absorbed. Any starch that was not digested in the small
intestine will be worked on by microbes – which can cause gas and colic. Some B vitamins and vitamin K will be
synthesized in the large intestine. (Definition of synthesis: the combining of
parts to form a whole.)
There are five sections that make up
the large intestine: the cecum, the large colon (which consists of the right
and left ventral colon, pelvic flexure; and the right and left dorsal colon),
the transverse colon, the descending colon (small colon), and the rectum.]
The cecum is a fermentation vat. It has been described as a comma shaped
organ. The cecum is about 4 feet in length and has a normal capacity of
approximately 8 gallons. The size can
vary according to the quality of roughage being fed to the horse. The entrance and exit openings are both
located at the top of the cecum. This
can cause problems resulting in colic if the organ becomes compacted with
non-digested material. Most feed remains
in the cecum for about 7 hours.
The cecum is located on the right side
of the horse. It is in a similar
location as our appendix. Though, while
our appendix can be removed, the horse needs his cecum.
(Caecum is the United Kingdom spelling.)
Within the cecum are microbes that aid
in the digestion of cellulose, fiber, and any remaining soluble
carbohydrates. These microbes are
somewhat specific as to what they digest.
If a drastic feed change occurs the balance of the bacteria and protozoa
is disrupted and colic can result. Any
change of feed (concentrates or forage) must be made over a period of about 3
weeks, so the microbe population can adjust.
A horse that has a hay belly is the
result of an expanded cecum. Poor
quality fiber has accumulated in the cecum and can remain there for up to 72
hours. Switching to less mature hay will
be more beneficial to the horse and prevent a hay belly from developing.
For
more information about the cecum please go to: http://www.thewayofhorses.com/08_11_cecum.html
The cecum then leads to the large
colon. The opening leading from the
cecum to the large colon is about a 3-4 cm hole. It is a prime spot for blockages to occur.
The large colon is approximately 10-12
feet long and is shaped like a horseshoe.
Microbial digestion continues in the large colon. Any remaining vitamins, fatty acids, and
water are absorbed. The large colon
holds about 20 gallons of material.
The large colon is made up of 5
segments (listed in the order in which the feed travels): the right ventral
colon, the left ventral colon, the pelvic flexure, the left dorsal colon, and
the right dorsal colon. The large colon
folds back on itself several times and is held in place by the bulk, which it
contains. At several points the colon
narrows and blockages can occur in these narrow passageways.
The design of the large intestine
requires plenty of good quality forage be available to the horse. If the colon becomes empty the chances of it
becoming twisted increases.
The remaining material then travels
through the transverse colon and into the descending colon (small colon). The transverse colon is a very narrow tube
and another primary spot for blockages.
The descending colon uses contractions
(peristalsis) which results in fecal balls forming. Any remaining moisture is also extracted in
the small colon. It measures about 12
feet long and is very narrow at about 3-4 inches in diameter. It holds about 5 gallons of material. The
small colon is also free to move and can become twisted.
The descending colon then leads to the
rectum. The rectum is a short straight
tube and acts as a storage area for the fecal balls until the horse expels
them.
Click
here for more pictures of the equine digestive system. The file is large so it may take time to load
if you have a slow internet connection or dial-up. Please email me if it will not load for you
and I'll try to send it another way.
Assignment:
1. At what age should a dental exam or care
begin? Feel free to do outside research
– you may ask your vet.
2. How often should horses have their teeth
examined?
3. Follow the steps outlined below and
send a report of your findings to Eleanor Blazer; elblazer@horsecoursesonline.com. If you have a recent exam performed by a
specialist you may send it along with your report, but still complete and
submit your own findings.
When writing your report please check
grammar, spelling and use proper formatting of your paper. Please do not send it in all caps and make
sure you use paragraphs. Most important
– please include your full name and correct email address.
Please tell me the age of the horse you are
using for the report.
1. Watch your horse eat. Notice if he drops grain or tilts his head to the side while chewing or if he dunks his hay in the water. These are all signs of potential problems.
2. While standing in front of your horse - be careful he doesn't throw his head and hit you with the end of his nose....place your fingers on either side of his cheek about where his back teeth start. Gently feel along the side of his jaw. See of you can feel the top row and the bottom row. Go down the top row...gently palpating...notice if he seems sore when you touch a certain area. Then do the same along the bottom row.
3. Lift
his lips and check his front and side teeth. Notice any chips and
how they are aligned. If he won't let you lift his lips to look at his
front and side teeth you need to practice. Notice if the gums are pink
and healthy.
If you detect any problems you'll need
to call a vet or equine dentist. This is not a thorough exam, but it
can help you decide if a more intense exam is needed. Every horse should
have their teeth examined at least once a year by someone who can check the
back ones - those are the teeth that develop points, which can lead to chewing
problems and utilization of feed.