Transcript digestion 2001

DIGESTIVE SYSTEMS
ANIMAL SCIENCE 110
Fall 2001
CLASSIFICATION
• Carnivore - simple stomach monogastric consume animal tissue as primary nutrient
source. Example: Dog & Cat.
• Herbivore - consume plant tissue
– Monogastric (Horse & Rabbit)
– Ruminant (Cattle, Sheep & Goats)
• Omnivore - consume plant & animal tissue
– Monogastric (Human & Pig)
Digestion includes all of the
processes (both chemical and
physical) which break down the
food into particles that can be
absorbed into the blood and
utilized for maintenance and
productive purposes.
MONOGASTRIC SYSTEM
• Mouth - includes teeth, lips & salivary glands.
– Mastication or chewing of food plus moistening and
lubrication of food prior to swallowing.
• Esophagus - Tube from mouth to stomach.
– Sphincter prevents backflow when stomach contracts.
• Stomach - Secretion of HCl and some enzymes +
mixing of food & enzymes.
MONOGASTRIC SYSTEM
• Small intestine - Major site of nutrient
absorption. Pyloric sphincter prevents
backflow.
– Bile, pancreatic juices are secreted into lumen.
– pH increases.
– Regions are called: doudenum, jejuneum &
ileum.
MONOGASTRIC SYSTEM
• Large intestine - Site of water absorption.
Small intestine empties in from the side.
– Blind pouch is called cecum (appendix)
• Rectum and anus - muscular area used for
storage of feces and defecation.
DEFINITIONS
• Enzyme is a complex protein that speeds up
a chemical reaction without being altered in
the process.
• Chyme is mixture of food and secretions
which flow from stomach to S.I.
• Fermentation is microbial conversion of
food into products that can be used by host
animal. Primarily bacteria and protozoa.
MONOGASTRIC DIGESTION
• Salivary amylase - initiates digestion in
mouth.
• Stomach secretes HCl, mucous, pepsin and
gastrin.
– Pepsin breaks proteins into polypeptides.
• Small intestine - duodenal cells secrete
hormones which stimulate release of bile
and pancreatic enzymes.
MONOGASTRIC DIGESTION
• Lipase hydrolyzes fats into fatty acids and
glycerol.
• Trypsin & Chymotrypsin convert proteins
and peptides into amino acids.
• Amylase converts starch to disaccharides
and monosaccharides.
• Absorption of molecules is both active and
passive. Blood carries nutrients to liver.
RUMINANT SYSTEM
• Mouth includes teeth, tongue and saliva but
no salivary amylase.
• Esophagus is same as monogastric.
• Stomach has four distinct compartments.
–
–
–
–
Rumen is the largest in the mature animal.
Reticulum (honeycomb)
Omasum (many plies or leaves)
Abomasum is similar to monogastric stomach.
RUMINANT SYSTEM
RELATIVE PROPORTIONS
Birth
2 mo.
30%
70%
Rumen
Reticulum
Omasum
5%
8%
70%
Abomasum
Maturity
80%
30%
7%
RUMINANT SYSTEM
• Small intestine, large intestine, rectum and anus
have similar functions as monogastric.
• Newborn ruminant is essential a monogastric for
the first few weeks. A well developed esophageal
groove allows milk to bypass rumen & move
direct to abomasum.
• Regurgitation and remastication of food (cud
chewing) is important.
• Neutral pH means no “heartburn”.
RUMEN FERMENTATION
• The anaerobic (CO2) system is ideal for microbial
fermentation - moist, warm and continual supply
of substrates.
• Microbes can digest cellulose as well as starch and
soluble carbohydrates and ferments them into
Volatile Fatty Acids.
– Acetic, Proprionic, Lactic & Butyric acids
• VFA furnish 60% to 80% of energy needs for a
mature ruminant.
RUMEN FERMENTATION
• VFA are absorbed across rumen wall and
are carried to liver by blood.
• Proteins in rumen are broken into peptides
and amino acids.
– Deamination results in free ammonia (NH4) +
carbon skeleton.
• Microbes resynthesize amino acids for their
own cell walls and cell structures.
RUMEN FERMENTATION
• Non Protein Nitrogen (NPN) such as urea is
hydrolyzed into NH3 + CO2.
• If adequate carbon substrate is present, the
free NH3 can be incorporated into microbial
protein.
• Urea is 45% N = 281% crude protein
equivalent. ( 45% x 6.25 = 281%)
• B vitamins are also synthesized in rumen.
RUMEN FERMENTATION
• Gases (carbon dioxide and methane) are
primary byproducts of rumen fermentation.
• Usually these gases are eructated or belched
out. If not bloat occurs.
• Bloat is a severe distension of the left side
of the ruminant and can result in death.
RUMEN FERMENTATION
• After fermentation, undigested feed
particles, bacteria, protozoa and fluid move
to the abomasum and become “food” for
digestion.
• Microbial protein is a fairly well balanced
protein source for the ruminant.
PROTEIN AS ENERGY
• Excess protein and amino acids can be used as an
energy source in both monogastrics and ruminants.
• The amino acids are deaminated and the ammonia
is excreted in urine.
• Protein is a more expensive energy source than
carbohydrates or fat.
• We attempt to feed protein to meet but not exceed
the requirement.
HORSE DIGESTIVE SYSTEM
• Similar to monogastric system prior to the
large intestine with two exceptions.
• Esophagus joins stomach at an oblique
angle so that horse cannot belch out gas or
chew a cud.
• Horse has no gall bladder. Bile is released
directly from liver to small intestine.
HORSE DIGESTIVE SYSTEM
• Caecum and colon in large intestine have
extensive fermentation.
• Microbial fermentation of fiber and any
soluble carbohydrates that escape
absorption in small intestine can be
fermented. VFA are 25%+ of total energy.
• Microbial protein and B vitamins are
produced but absorption is less efficient.