Transcript Introduction to Digestion

Beef Cattle:
Managing Ruminants
Beef Cattle Industry
Advanced Animal Science:
Principles of Industry
Sutherlin AST
September 15, 2015
The Ruminant Stomach
Rumination
• Ruminants bite off forage and swallow quickly,
then process the food
• Result of evolution – why?
• The following steps
are called rumination
Rumination
• “Chewing the Cud”
– Animal regurgitates large boluses of food which
were earlier swallowed
– Re-chewing food breaks
down for easier conversion
by bacteria/microbials
Rumination
• “Chewing the Cud”
– Added benefit: saliva acts as a “base” to
counteract rumen acid (more later)
Reticulum
• Honeycomb-like interior surface
Reticulum
• Helps to remove foreign matter from the food
material
• Material that “sinks” into the reticulum is
there for the life of the animal
Telephone Cord
Reticulum
• Some material can
cause damage, called
“hardware disease”
• Solution: bolus
magnet is slipped into
animal to collect
material, stays inside
for life
Rumen
• A large fermentation tank
• pH is about 6, depending on diet
Rumen
• Allows for bacterial and chemical breakdown
of fiber
– A very thick, muscular wall
– Fills most of the left-side of the abdomen
Rumen
• Walls of the rumen contain papillae
– This where the bacteria live
– Up to 1cm long
• The rumen can be
up to 55-65 gallons
in size
– About 80% of adult
stomach, but only
30% of calf stomach
Rumen
• Microbials process plant matter that normally
couldn’t be digested
• Products released include VFA (Volatile Fatty
Acids)
– absorbed directly into bloodstream for energy
Omassum
– Round and muscular
– “Grinds” the food material and prepares it
for chemical breakdown
– Removes excess water
Abomassum
– Very similar to the stomach of nonruminants
– About 7-8% of total stomach
– Majority of chemical breakdown of food
material occurs
Abomassum
– Mixes in digestive enzymes (pepsin, rennin,
bile, etc)
– pH is closer to 2.4
Rumen Microbes
•
•
•
•
There are 1010 to 1012 cells/mL
Continuous culture fermenters
Live in pH of 6.8-7.0
39 degrees C
Rumen Microbes
Rumen Microbes
• Divided between three kingdoms
– Bacteria
– Protista
– Fungi
The Relationship
• Microbes and ruminants have a symbiotic
relationship
– Both gain from the partnership
The Relationship
• Microbes provide to the ruminant:
– Digestion of cellulose
• Couldn’t digest roughages without microbes!
The Relationship
• Microbes provide to the ruminant:
– Production of high quality protein
• 50-80% of Nitrogen (N) is absorbed from microbes
• Protein has high value
The Relationship
• Microbes provide to the ruminant:
– Produce B vitamins
• Meets ruminants needs in most conditions
The Relationship
• Microbes provide to the
ruminant:
– Detoxify toxic compounds
• Example – Mimosine in Leucaena
cause problems in animals (poor
growth, reproduction/hair loss)
The Relationship
• Microbes provide to the ruminant:
– Detoxify toxic compounds
• Hawaiian ruminants, but not Australian ruminants,
have microbes that degrade mimosine so Leucaena can
be fed
– Transferred rumen fluid to Australia
– Inoculated rumen
– Fed Leucaena
The Relationship
• Ruminants provide to the microbes:
– Housing
• Reliable heat (39 degrees C +/- 2)
• Guaranteed for 18 to 96 hours depending on
diet/animal
– Straw-fed water buffalo – longest rumen residence time
– Small selective browsers (mouse deer) – shortest time
The Relationship
• Ruminants provide to the microbes:
– Garbage removal
• Absorption of VFA’s (energy for ruminant)
• Eructation
– Release of gas (CO2 and CH4)
• Passage of indigestible residue/microbes
The Relationship
• Ruminants provide to the microbes:
– Nutrients
• Animal eats!
• Saliva provides urea (N source for bacteria)
The Relationship
• Ruminants provide to the microbes:
– Neutral environment
• pH 6.5 to 7.0
• Saliva contains bicarbonate/phosphate buffers to
balance acid from microbes
The Relationship
• Ruminants provide to the microbes:
– Neutral environment
• If the pH was 5.7 rather than 6.5…
– 50% less microbe activity
– Rate of carbohydrate use decreased
Factors that Reduce Microbial Growth
• Rapid ration change
– Takes 3-4 weeks for microbes to stabilize
• Feed restricted amounts
Factors that Reduce Microbial Growth
• Feed lots of unsaturated fat
– Bacteria do not use fat for energy
• Feed lots of non-cellulose carbohydrates
– Causes rumen acidosis
Factors that Promote Microbial
Growth
• Maximum dry matter intake
• Balanced carbohydrate and protein fractions
– Bacteria need both energy and N for amino acid
synthesis
• Gradual ration changes
– Maintain rumen pH
• Keep feed available at all times