The largest cost associated with sheep production is feed. To achieve
desired efficiency of feed utilization requires you to know each of the production phases
of the sheep, knowledge of the digestive tract, ruminal fermentation, digestive and
absorptive processes, and nutrient metabolism and distribution in the body.
The main components of the sheeps digestive tract are: esophagus, reticulum, rumen,
omasum, abomasum, small intestine, cecum, large intestine, and rectum.
Once feed has been consumed, it travels down the esophagus to the rumen and reticulum,
which are the first two compartments of the ruminant stomach. The ingested feed is
swallowed with little chewing. After an extended grazing session or consumption of
feedstuffs, the process of rumination begins. Rumination happens because of the constant
contractions of the rumen-reticulum, which move the feed mass forward to come in contact
with the lower opening of the esophagus. The mass moves back up the esophagus where it is
rechewed. Mature sheep will spend eight hours or more each day ruminating their feed to
reduce the particle size.
The rumen-reticulum is a fermentation chamber that hosts large microbial populations. This
is the chamber that enables ruminants to derive energy from fibrous feedstuffs. The
end-products of fermentation are absorbed into the bloodstream through the walls of the
rumen and reticulum or the omasum. Water and some fermentation end-products are absorbed
in the omasum.
End products leaving the omasum passes to the abomasum ( true stomach ). The abomasum
secretes gastric juices, hydrochloric acid and digestive enzymes, into the digesta
starting enzymatic digestion.
The small intestine is where the digesta is exposed to intestinal and pancreatic enzymes,
as well as bile from the liver. Protein, starch, and sugars are enzymatically digested
here but fiber ( such as cellulose ) that excaped the fermentation process in the
rumen-reticulum cannot be digested in the small intestine. Lipid (fat) digestion also must
occur in the small intestine. The 80 foot long section of the small intestine is where the
absorption of the products from enzymatic protein, carbohydrate, and lipid digestion takes
place.
The cecum is unimportant in the rumimant because of the digesta having prior exposure in
the rumen-reticulum for breakdown. The large intestine is the second site of fermentation
and is where water and end-products from passing digesta is absorbed. Undigested
feedstuffs are then excreted through the rectum as feces.
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Rate of Passage
Liquids pass faster through the GIT faster than solids. Faster rates of passage occur
with highly digestible diets that are of small particle size, diets fed at high daily
intakes, and diets that are consumed frequently. High fiber or roughage diets have a slow
rate of passage. It usually takes about 12 to 24 hours for undigested food to show up in
the feces as solid material (or ten percent of the total that will be passed). About 80
percent will be excreted within 70 to 90 hours with it taking seven to ten days for all
particles of a meal to make it completely through the gastrointestinal tract.
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Reticular-Ruminal Fermentation
A very large microbial population inhabits the rumen and reticulum consisting of
bacteria, protozoa, and fungi living in a regulated environment. Constant ingestion of
feedstuffs and regurgitated digesta occurs here along with absorption of fermentation
end-products and digesta passage out of the rumen-reticulum. The rumination process is
important to maximize exposure of ingested materials to the microorganisms. The main
function of the microorgranisms is to digest fiber components of feedstuffs. During
fermentation in the rumen, dietary carbohydrates and proteins are completely degraded and
used by the microorganisms before the abomasum and small intestine do their digestive and
absorptive duties.
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Postruminal Digestive and Absorptive Processes
After the feedstuffs pass through the rumen and reticulum they come into contact with
acidic conditions in the abomasum. This acid denatures the proteins so enzymes can go to
work on them. Digestion in this area is of primary importance in allowing animals to use
it for their productive functions.
Fat digestion takes place in the small intestine when the lipid first comes into contact
with bile from the liver. Lipase enzymes then digest the lipids. These fatty acids are
then absorbed across the intestinal wall, made into triglycerides, and transported
throughout the body.
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Nutrient Metabolism
Proteins, carbohydrates, lipids, minerals, vitamins, and water provided by the diet are
used to maintain the animal first and then what is left over after their requirements is
then used for productive functions. 50 to 100 percent of the daily intake of sheep is used
for maintenance alone, depending on evironmental conditions and the quality/quantity of
the feedstuff that your are feeding them.
Primary source of energy for the sheep are VFA or volitale fatty acids. Amino acids are
the primary end-products of digestion in the ruminant. After they are absorbed in the
small intestine they enter the bloodstream where they travel to the liver. The liver then
directs them to the body tissues where they are needed. The excess is then degraded and
the nitrogen part is converted to urea. The urea is then either recycled to the digestive
tract or excreted.
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