Chapter 4. The Digestive and
Metabolic Systems
I. Utilization of feeds by livestock
A. There are 4 steps of feed utilization:
1. Digestion
- the chemical and physical
breakdown of feed particles in
the gastrointestinal tract (GIT).
2. Absorption
- movement of nutrients through
the wall of the gastrointestinal
tract and capillary walls into
the circulatory system.
Chapter 4. The Digestive and
Metabolic Systems
3. Circulation of absorbed nutrients
4. Cellular metabolism
- all physical and chemical
processes occurring within a
biological system.
Blood: Amino acids,
monosaccharides ,
lipids, minerals,
vitamins
Cell
Molecules
and
compounds
Chapter 4. The Digestive and
Metabolic Systems
Order of Feed Digestion: Swine
diet (%)
1. Carbohydrates – Mouth 60
2. Protein – Stomach 15
3. Fat - Large intestine 3
Chapter 4. The Digestive and
Metabolic Systems
1. Prehension - the act of obtaining food
a. shape of lips
b. type and arrangement
of teeth
c. tongue structure
2. Mastication - the mechanical breakdown of feeds into smaller particles
a. increase surface area
b. dental pad vs. incisors vs.
gizzard
B. Ingestion and Breakdown of Feeds
Chapter 4. The Digestive and
Metabolic Systems
3. Saliva secretion
a. greatest during mastication (a cow secretes ~100 lbs of saliva per day)
b. amylase present in non-ruminants – breakdown of carbohydrates in mouth
c. sodium bicarbonate present in ruminants - regulates pH in rumen
d. lubricant
Chapter 4. The Digestive and
Metabolic Systems
4. Enzymatic digestion
a. releases nutrients
b. begins in mouth in non-ruminants
1. stomach: gastric juices (HCL) (ACIDIC)
- pepsin breaks down proteins
- lipase breaks down fat into
fatty acids and glycerol,
but not very effective in
the stomach.
Chapter 4. The Digestive and
Metabolic Systems
- renin coagulates milk in
young ruminants to slow the
passage through the GIT.
2. small intestine: digestion and
nutrient absorption is most active
- bile released from the gall
bladder that aids in
digestion of fat.
Chapter 4. The Digestive and
Metabolic Systems
- protease released from the pancreas that aids in digestion of protein.
5. Movement of partially digested food (chyme).
a. Peristalsis - muscle contractions beginning at the pharynx and continuing until excreted.
Source: http://mycozynook.com
Chapter 4. The Digestive and
Metabolic Systems
6. Absorption
a. mostly occurs in the small intestine (60
feet long in a 100 lb pig)
b. villi – fingerlike proliferations in the
small intestine that act to increase the surface area
Chapter 4. The Digestive and
Metabolic Systems
6. Absorption (cont.)
c. energy needed, ATP, to absorb
monosaccharides, fatty acids, and amino acids
d. minerals – simple filtration
e. vitamins – blood or lymph
Chapter 4. The Digestive and
Metabolic Systems
7. Nutrient storage a. guaranteed nutrient
supply
b. important storage
sites: bones, liver, adipose
tissue
8. Nutrient Utilization
6CO2 + 6H2O + Energy Chlorophyll C6H12O6 +6O2
Cell Enzymes
Photosynthesis
Oxidation
Chapter 4. The Digestive and
Metabolic Systems
II. Nonruminant (monogastric) digestive system
A. PIG: Bolus of feed pushed down esophagus by peristalsis into a single stomach compartment.
- peristalsis: a process by which muscular contractions propel food material through the digestive tract.
Pig GI tract : mouth esophagus stomach
small intestine (duodenum, jejunum, ileum) large intestine
rectum anus
cecum
(The small intestine of a 100 pound pig has is nearly 60 feet long!)
Chapter 4. The Digestive and
Metabolic Systems
1. stomach is small which leads to:
a.) frequent feeding: a 2-wk old pig has a capacity to hold 0.7 lbs and at 7-8 months (200 lb) a pig can hold 8.5 lbs, whereas a 100 lb lamb has a 24 lb stomach capacity.
b.) low bulk and fiber
Chapter 4. The Digestive and
Metabolic Systems B. Poultry: Bolus of feed pushed
down esophagus by peristalsis
into the crop (i.e., temporary
storage compartment), into the
proventriculus, and then into the
gizzard.
- proventriculus: enlarged section
of the esophagus a.k.a. the
glandular stomach because of HCl
secretion and digestive enzymes.
Chapter 4. The Digestive and
Metabolic Systems
- gizzard: structure with powerful
muscles that grinds food particles to
smaller sizes.
1. No organ named stomach in poultry!
Poultry GI tract : mouth esophagus crop
proventriculus gizzard sm. Intestine lg. intestine
cloaca vent
Ceca
Chapter 4. The Digestive and
Metabolic Systems C. Horses and Rabbits (neither a
ruminant nor a non-ruminant): Bolus of feed pushed down esophagus by peristalsis into a single stomach compartment where digestion begins.
1. digestion of fibrous material does not occur in the stomach.
2. microbes (mostly bacteria) in cecum and large intestine.
a. volatile fatty acids (VFA’s): acetic, propionic, and butyric acid serve as energy sources.
b. B & K Vitamins are synthesized.
“Coprophagy”?
Chapter 4. The Digestive and
Metabolic Systems
C. Horses and Rabbits
“Coprophagy”
Horse GI tract : mouth esophagus stomach
small intestine cecum sm. & lg. intestine rectum
anus
(colon)
Chapter 4. The Digestive and
Metabolic Systems
III. Ruminant digestive system
A. Cattle: Bolus of feed pushed down esophagus by peristalsis into a four compartment stomach where digestion begins.
1. Stomach compartments:
a. rumen – largest, bacterial digestion largely occurs,
located on left side (pH 7.0).
b. reticulum – mostly bacteria,
located in front of rumen.
Chapter 4. The Digestive and
Metabolic Systems c. omasum – receives food from
reticulo-rumen, grinds feed contents (digesta) and absorbs H20.
d. abomasum – true stomach
Chapter 4. The Digestive and
Metabolic Systems
2. Hardware disease
3. Rumination:
a.) bolus of feed at the cardia (lower opening into
the esophagus) is pulled and
pushed by reverse peristalsis
into the mouth.
b.) bolus rechewed slowly
and re-ensalivated.
c.) occurs several times daily, 8 hr/day.
Chapter 4. The Digestive and
Metabolic Systems
4. Ruminal micro-organisms:
Bacteria, fungi, protozoa, yeasts, actinomyces
(cellulolytic vs. amylolytic bacteria)
a.) convert cellulose and starch to an
energy source, volatile fatty acids (VFA’s).
b.) convert plant protein and non-protein
nitrogen (N2) into
microbial protein.
c.) synthesize K
and B vitamins
Development of ruminant GIT:
Birth 4 mos Mature
1. Rumen 25% 75% 80%
2. Reticulum 5% 5% 5%
3. Omasum 10% 9% 7%
4. Abomasum 60% 11% 8%
Chapter 4. The Digestive and Metabolic Systems
Functions of the Liver:
1. Degrading & rebuilding of amino acids
2. Detoxifying excretion products
3. Building blood cells
4. Storehouse for all nutrient classes
5. Other vital functions
Chapter 4. The Digestive and Metabolic Systems
