Digestive System of Animals
Animal Science Frameworks
Presentation Unit 3.1
Mr. Sullivan
Digestion
Purpose: reduce feed particles to molecules
that can be absorbed into the blood
• Mechanical breakdown of food
– chewing
• Chemical breakdown of food
– HCl in the stomach
– enzymes
• Contractions of digestive tract
Animals are classified by the
types of food they ingest
• Carnivore - animal products
– Dogs, Cats
• Herbivore - plant products
– Cattle, Sheep, Goats, Horses
• Omnivore - combination of plant and
animal products
– humans, pigs
Animals are also classified by
the type of stomach they have
• Monogastrics or non-ruminants
• Ruminants
Monogastric Animals
Monogastric – one or simple stomach
structure
• mostly carnivores and omnivores
» Very simple: mink and dog
» Cecal digestion: horse, rabbit or rat
» Sacculated stomach : kangaroo
Ruminant Animals
Ruminant - 4 compartment stomach with the
compartments before the “true” stomach
• herbivores
» cattle, sheep, goats and pseudoruminants (llamas)
Digestion
• Prehension
– Bringing the food to the mouth
• Upper limbs, head, beak, claws, mouth, teeth and
lips
• Mastication or chewing
– To crush the food, increase surface area and
allow enzymes to act on molecules
• Carnivores need only to reduce the size of the
particle
• Herbivores must chew continuously (40-50,000
times a day)
Monogastric Animal
Digestive Tract
Basic anatomy
mouth
stomach
small intestine
large intestine or colon
Monogastric Animal
Digestive Tract
• Feed passes from the mouth to the stomach
through the esophagus
• To reduce the size of the feed particles
• From the stomach it passes through the
– duodenum (first part of the small intestine)
• Bile and pancreatic secretions enter here
– jejunum (second part of the small intestine)
• Absorption of nutrients
– ileum (third part of the small intestine)
• To split food molecules and absorb nutrients
Monogastric Animal
Digestive Tract
• Large Intestine
• water absorption
• feces formation
• Rectum
Human and Pig Similarities
•
•
•
•
Both are omnivores
Cannot synthesize B complex vitamins
Cannot synthesize amino acids
Can become obese with increased food
intake
Monogastric Animal
Digestive Tract
• Exceptions
– herbivores
• horses have a cecum (blind anterior end of the
colon) where feed is fermented
– Cecum is posterior to optimum feed absorption area,
thus advantages of the ruminant animal is lost
Enzymes of the Digestive Tract
Enzyme names often end in -ase
and
begin with a description of the substrate they
act upon
Enzymes of the Digestive Tract
Enzyme
Amylase
Substrate
Product
Starch
Dextrin,
Disaccharides
Chymotrypsin Peptides Amino Acid
Peptides
Lactase
Lactose Glucose
galactose
Enzymes of the Digestive Tract
Enzyme
Lipase
Substrate
Lipids
Pepsin
Peptidase
Sucrase
Trypsin
Protein
Peptides
Sucrose
Protein
Product
Fatty acids
glycerides
polypeptide
amino acid
glucose
polypeptide
Monogastric Digestion
• Enzymes help breakdown large molecules
– Mouth
• amylase in saliva of humans and pigs breaks down
starch to disaccharides and dextrin
– Stomach
• HCl - creates acidic environment
• pepsin - breaks proteins down polypeptides
Monogastric Digestion
• Enzymes help breakdown large
molecules
– duodenum
• Cells release hormones that act on pancreas
and gall bladder
– secretin
– pancreozymin
– cholecystokinin
Monogastric Digestion
• pancreas
– lipase
• lipids to fatty acids and glycerides
– trypsin
• proteins to polypeptides
– chymotrypsin
• peptides to amino acids and peptides
– amylase
• starch to disaccharides and dextrin
Monogastric Digestion
• gall bladder
– bile
• produced in the liver
• emulsifies fats
• alkaline to neutralize stomach contents that are
acidic
• small intestine
– amino acids, fatty acids and monosaccharides
are available for absorption
Ruminant Digestion
• mouth
• esophagus
• rumen
• reticulum
• omasum
• abomasum
• small intestine
• large intestine
Ruminant Digestion
• rumen - 40 gallons in a cow
– large fermentation vat
– covered with papillae to increase the surface
area
– microorganisms digest cellulose
– microorganisms synthesize amino acids from
nonprotein nitrogen
– microorganisms synthesize B-complex
vitamins
Ruminant Digestion
• reticulum - 2 gallons in a cow
– lining looks like a honeycomb
– interacts with rumen to mix contents
Ruminant Digestion
• omasum - 4 gallons in a cow
– many folds, perhaps to grind feed
Ruminant Digestion
• abomasum - 4 gallons in a cow
– true stomach
Ruminant Digestion
• Ruminants eat forage rapidly
– they regurgitate food (cud)
– and chew it again and swallowed
• Rumination - continuous reguritation,
chewing and swallowing
• Eructation - elimination of gases (methane
and carbon dioxide) in the rumen from
fermentation
Rumen Microorganisms
• Bacteria and Protozoa
– rumen environment is moist, warm, and
provides a constant supply of nutrients
– entire population of organisms depending on
the kind and quality of the feed
– when they are washed out of the omasum into
the abomasum the acidic environment kills
the microorganisms
– provide amino acids and some energy
Ruminant Digestion
• Ruminants to not secrete amylase in their
saliva
• bacteria and protozoa in the rumen and
reticulum utilize starches and sugars- no
glucose available for the ruminant
– microorganisms do produce volatile fatty
acids (VFA) that are absorbed and converted
to energy
• acetic, propionic and butyric acids
• major source of energy
Energy Pathways in the
Ruminant
From Rumen to Abomasum
Injestion materials
Cellulose
Starch
Fat
Complex Sugars
Glucose
VFAs
Energy Pathways in the
Ruminant
Liver
VFAs
Glucose
Ruminant and Monogastric
Absorption in the small intestine
• passive transport
– diffusion by concentration
• active transport
– villi engulf molecules
• to bloodstream or lymph system
Rumen Microorganisms
• Bacteria and Protozoa
– rumen environment is moist, warm, and
provides a constant supply of nutrients
– entire population of organisms depending on
the kind and quality of the feed
– when they are washed out of the omasum into
the abomasum the acidic environment kills
the microorganisms
– provide amino acids and some energy