DIGESTION
ANSC 101
Definition
• Digestion is all of the chemical and
physical changes that food
undergoes to be absorbed.
• Absorption takes place as nutrients
enter the body from the digestive
tract.
GI Tract – Digestive System
• Mouth
• Esophagus
• Stomach
• Small intestine
• Large intestine
• Liver,
• gall bladder
• pancreas
MOUTH
• Teeth
• Tongue
• Salivary glands
Esophagus
• Birds
– CROP
• Mammals
Stomach
• Complexity varies
– Simple in monogastrics (nonruminants)
– 4-chambered complex stomach of
ruminant
Functions of Stomach
• STORAGE
• Chemical Digestion
Non-Ruminant Stomach
• 4 regions
– Esophageal
– Cardiac
– Fundic
– Pyloric
Poultry
• “Stomach” is called
PROVENTRICULUS
• Has same functions as mammal
Gastric Secretions
1. HCL
1. Activates pepsinogen to pepsin
2. Does some digestion itself
2. Gastric Enzymes
1. Pepsin
2. Lipase
3. Renin
3. Mucin
4. Intrinsic Factor (for absorbing B12)
Ruminant Stomach
• 4 compartments
– Rumen – big fermentation vat
– Reticulum – “hardware stomach”
– Omasum – “many plies”
– Abomasum – “true stomach”
Rumen Microbiology
• Bacteria do 3 things
– Digest CHO to VFA’s (including cellulose)
– Remodel proteins, manufacture essential
amino acids and utilize NPN
– Manufacture B vitamins
Summary of Rumen Action
• CHO ——> VFA’s
• Proteins ——> Bacterial protein
• Fats ——> hydrogenated but not
much utilization
• B Vitamins ——> synthesized
• Vitamins ADE ——> needed in diet
Small Intestine
• Duodenum
• Jejunum
• Ileum
Digestive Juices
• Bile
– Produced in the LIVER
– Stored in the Gall Bladder
• Pancreatic juice
– Exocrine secretions
• Sodium carbonate and bicarbonate
• Enzymes
– Endocrine secretions
• Insulin
• Glucogon
Digestive Juices continued
• Secretions from small intestine wall
– They digest disaccharides, peptides, etc to
forms that can be absorbed
Absorption
• Molecules must get from gut lumen
into brush border of epithelial cells,
then across cells into blood or
lymph.
• Occurs by diffusion, facilitated
absorption and active absorption.
Large Intestine
• Ascending, transverse and
decending colon
• FUNCTIONS:
– Storage
– Absorption of water
• Special role of cecum
Cecum
• Blind pouch at junction of small and
large intestine
• Developed in nonruminant
herbivores (horses, rabbits)
• Provides post-absorptive
fermentation vat
– Digests cellulose, Does NOT provide
protein
Horse, Rabbit
Metabolism defined | CHO
• Use by the body of nutrients and
metabolites
• Carbohydrates – converted to tiny
amounts of glycogen, used for
blood sugar, or converted to ATP
(energy), stored as fat
Metabolism of Fats
• Go to liver, then to fat storage, or
used for energy
Metabolism of Proteins
• Amino acids enter blood stream and
supply cells with amino acids for
protein synthesis
• Amino acids not quickly used are
deaminated and used for energy
Metabolism of Energy
• Energy in the chemical form of ATP
is either used by the tissues or
stored in animals as fat
Metabolism of Vit’s & Minerals
• Vitamins are involved in tissues
throughout the body, maintaining
structures and participating in
chemical reactions
• Minerals make up structural
components and activate enzymes,
maintain water balance, and more.
End of Digestion, 101
• Next we will consider where animals
will GET those nutrients:
• FROM FEEDS
Animal Feeds
• 2 major catagories of energyproviding feeds are:
• Concentrates
• Roughages
Concentrates
• Grains
– High in energy, low in fiber, low in protein,
low protein quality
• Protein supplements
– From oil seeds (like soybean meal)
– From animal byproducts, fish byproducts,
etc.
Roughages
• Not used or used poorly by
nonruminants
• CATAGORIES
– Grasses
– Legumes
– Crop residues
Grasses
• Grow “everywhere”
• Moderate energy source
• Low protein source
• Low calcium levels
• Good for meeting maintenance
needs
Legumes
• Moderate sources of energy
• High protein levels
• High calcium levels
• Not adapted to grow well
everywhere
• Where they do grow, they increase
soil fertility
Legumes
•
•
•
•
•
Alfalfa
Red clover
White clover
Sweetclover
Alsike
Crop Residues
• Provide bulk
• Some but low levels of energy
• Useful in helping meet maintenance
• Very cheap except for processing
and transportation costs
Crop Residue - Corn Stover
Forages can be fed as:
• Pasture
• Hay
• Silage
Pasture
Hay
Silage
Ration Balancing
• The task of meeting the animals
nutrient requirements with the
feeds provided to the animal
Ration Balancing
1. Determine animal’s requirements
1. From NRC, Extension publications, etc.
2. Get feed’s nutrient content
1. From analysis or feed tables
3. DO THE MATH
1. By hand or
2. By computer program
Example by Hand
• Say pig needs 16% CP, & using Corn
with 8% CP and Suppl. with 36% CP.
16 = .08X + .36(100-X)
16 = .08X + 36 - .36X
16 – 36 = .08X - .36X
- 20 = - .28X
X = -20X/-.28X = 71.4% corn
100 – X = 28.6% supplement
• Example by Computer if there is
time
Feeding programs
• Pigs and poultry are fed primarily
“simple” diets based on corn for
energy, SBM for protein, and
fortified with vitamins and minerals.
• Full feed growing/finishing pigs
• Limit feed pregnant sows & gilts
• Use antibiotics judiciously
Beef and Sheep
• Summer rely on range, pasture
when possible
• Winter: need preserved feeds:
– Hay
– Silage
– Grain as needed
• Feed cows, ewes according to stage
of production
– Needs are low at maintenance
– Needs increase in last 1/3 gestation
– Needs are high during lactation
• Maintain animal’s body condition
Feeding Beef Cows
• For MOST, that means:
– Spring & summer = Pasture
– Fall – Winter = Preserved feeds
– Late Winter (late gestation) supplement
• Grain
• Protein as needed
– Test hay to know what you are feeding
• Allow calves to grow
(backgrounding)
• Then place in feedlot on high
energy feeds (grain)
Feeding Dairy Cattle
• Requirements are very high due to
high milk production
• Intake is high (4% BW vs ~2% for
beef)
• Feed grain for high production (up
to 60% of total DM)
Dairy feeding
• Must maintain at least 40% forage in
the ration
End