You see it go in, you see it come out,
but what happens to your horse’s feed in between?
Your horse is a grass-eating machine!
He has evolved over millions of years to survive on a diet of nothing
but grass and although he is adaptable and can eat grain and hay when
we need him to, his digestive system is designed as and will always
work best as a perfectly oiled grass processing system. Ever been told
you eat like a horse? It is true, horses eat a great deal, usually
more than any human could hope to compete with! Even if your horse was
the same size and weight as you, he would need to eat a lot more than
you do to maintain his weight and have the energy to run around and
jump fences. Horses have evolved as grazers and have developed a
special way of processing grass and other forage to get the most out
of every mouthful.
Because grass doesn’t have much energy compared to the foods we eat
like meat, potatoes and vegetables, horses have to eat a lot more to
supply their everyday requirements. In the wild, horses eat slowly for
most of the day and night, they graze over large areas for up
to 18 hrs per day, picking out the most nutritious grasses. Food is
moving through them almost constantly, as you will know all too well
if you have the responsibility of cleaning a horses stable after you
left him with a large haynet overnight! If you could look inside your
horse, you would see that his digestive system takes up a very large
amount of the space in his body (see above). This reflects the
importance of the digestive system to the well being of the horse. The
system is well adapted to dealing with tough fibrous material such as
hay, pasture and chaff.
The four major sections of this system
is what we will discuss in this article.
• The mouth and teeth – where food is chewed and ground into small
pieces
• The stomach – where acids and enzymes are added to start dissolving
food particles
• The small intestine – where most parts of the food are digested and
absorbed into the blood
• The large intestine – where the horse allows it’s host of resident
bugs to digest the remainder of the food so that the horse can use it,
leaving the rest to pass out of the horse as feaces.
The Mouth and Teeth
Looking inside your horses mouth you see lots of large teeth. These
teeth go right to the back of the horses jaw and are wide, flat and
perfectly suited to grinding and crushing hay and feed. The tongue
helps to ball the food up and move it around the mouth as it is
chewed. Horses chew about 60,000
times
per day and so have very strong jaw muscles. Hay and grass needs to be
thoroughly chewed before it can pass on to the next part of the
system. If your horse cannot chew properly, it makes the job of the
digestive system that much harder, and the horse will not get the full
benefit out of his food. It is very important to get your horses teeth
checked and rasped at least once per year, and more regularly for
older horses. Chewing makes the food wet with saliva and softer. Food
is ground into small pieces for the next part of digestion: the
stomach.
The Stomach
Food passes from the mouth down a pipe called the oesophagus to the
stomach. The horses stomach is quite small and cannot hold a lot of
food at one time. If you give your horse a very large meal at one
time, and he eats it quickly, he may show signs of colic as the
stomach gets swollen with too much food at once. It is important to
obey the ‘feed little and often’ rule with horses to avoid these
problems. As your horse chews
and eats his hay, the food goes down and passes through the stomach to
the next stage fairly quickly (about 20 minutes from one side to the
other) so there is a continuous stream of food passing through. In the
stomach, the chewed food is mixed with strong acids and enzymes which
are made by the cells in the stomach wall. These break down and
dissolve the food allowing some parts to be absorbed. All around the
stomach and intestines there is a very good blood supply. When the
food is dissolved, some parts can pass through the stomach and into
the blood. Once in the blood, the food goes to parts of the body that
need it, like the muscles during exercise. If the horse doesn’t need
the energy right away, the food is stored for later use either in the
muscles, liver or as fat. Once food has passed through the stomach it
goes to the small intestine.
The Small Intestine
The small intestine is quite long, around 21-25m in length. It is the
first real site of digestion and is the part of the system where grain
and concentrate feeds are absorbed. Sugar, protein, fat, minerals,
vitamins and electrolytes are taken up from the small intestine into
the blood for use in the body. The acid of the stomach must be
neutralised to prevent the strong acid from dissolving the walls of
the small intestine. Bile and other alkaline secretions do this job as
soon as the food enters the small intestine. Digestive enzymes are
added to the partially digested food in the small intestine and these
need a fairly neutral environment to work properly. Food spends
between one and eight hours travelling through the small intestine.
The protein, fat and about half the available carbohydrate contained
in the feed is dissolved and absorbed into the blood, leaving only the
tough fibre portion which passes on to the large intestine. If you
feed your horse a large grain meal, or if he gorges himself on rich
green pasture, then there may still be some sugar left when the food
goes to the large intestine. This can be very bad for your horse as it
can cause colic or laminitis. The quantity of digestive enzymes in the
small intestine increases slowly in response to changes in diet so
changes should be made slowly to ensure complete digestion in the
small intestine. Some grains have a very tough outer coating which can
only be digested in the large intestine. This coating must be broken
before the starch inside can be digested, so these grains should not
be fed whole. This is why many grains are crushed, cracked, pelleted
and cooked, so that the starch can be more thoroughly digested before
reaching the large intestine.
The Large Intestine
Although only 7-9m long, the large intestine is very wide, holding a
large amount of partially digested food, water and microbes. It is
made up of a large section called a caecum, and two large sections
called the colon. The large intestine is designed as a fibre digestion
site. Horses do not have the ability to digest some forms of
particularly tough fibre found in hay and grass. To get over this
problem, horses have a very special relationship with a number of
bacteria and other small bugs (protozoal and fungal microbes) that
live in the large intestine. These good bacteria live and work their
entire lives inside the horse, digesting the fibrous portion of the
diet and turning it into a form that the horse can use. The bacteria
benefit by having a constant food supply in a protected environment,
and the horse benefits from being able to use energy from the portion
of the diet that it would not otherwise be able to get to. Fibre
digestion takes quite a long time and it can take 50 – 60 hours for
food to get through this part of the system. The microbes produce some
heat as they work which is why it can be very beneficial to feed the
horse more hay in the cold winter months. Feeding a lot of fibre means
that the hindgut will get very full, the horse drinks lots of water
when he eats a large amount of hay and together these make his belly
look big and round. Horses that get a lot of grain and not so much hay
will have a leaner, more greyhound shaped belly, like race horses and
trotters. Bacteria and microbes are fairly temperamental and are
easily upset by changes in their environment which is why we have to
be very careful about what we feed. If you change the diet too
quickly, the microbes need time to adjust to the new food source. If a
lot of starch (from grain or green grass) makes it through to the
large intestine, the bacteria will process it, but unlike the useful
product of fibre digestion, they produce acid, which ultimately kills
some of the bacteria. When bacteria die, they release toxins, and
these are responsible for colic or laminitis after a big meal.
The digestive system of the horse is
perfectly suited to their natural diet of grass. By domesticating
horses and asking them to do work, we have had to find ways of feeding
them a diet with more energy, and one that can be fed in the
confinements of a paddock or stable. We have to be very careful to try
and mimic the eating patterns of horses in the wild so that the
digestive system receives a continuous flow of food an is not
overwhelmed with large high starch meals that we feed for energy. It
is best to feed at least two or three small meals of grain per day
with plenty of hay, pasture or chaff. If your horse does not have to
work too hard he will manage very well on a diet of hay or pasture
alone. Horses are designed to eat grass, and the more natural roughage
we can feed, the better the digestive health of the horse will be and
the less likely you are to see problems like colic or laminitis.
Article reproduced
courtesy of www.ker.com
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