Lecture 43 11/28/23 Flashcards
What is fermentation?
chemical breakdown of a substance by microorganisms
Where does fermentation occur in foregut fermenters?
distinct compartments of the non-glandular stomach
Where does fermentation occur in hindgut fermenters?
cecum and colon
What environmental characteristics are needed for fermentation?
-neutral pH
-slow motility
-ability for microbes to survive and grow
What types of microorganisms are found in the rumen?
anaerobic bacteria, fungi, and protozoa
What are the interactions observed between the rumen microbes?
-waste of one organism is food for another
-synergistic digestion/microbes digest different things
-one microbe produces vitamins needed to promote the growth of others
Which substrates from plant cell walls can be broken down by microbes?
-cellulose
-hemicellulose
-pectin
Which substrate from plant cell walls cannot be broken down by microbes?
lignin
How does plant age impact lignin amounts?
plants accumulate more lignin with age
What happens to proteins and carbohydrates in ruminants?
rumen microbes use the same substrates that the host would use, potentially reducing digestion/absorption effeciency
What are the characteristics of volatile fatty acids?
-major fermentative end products
-main energy source for ruminants
-absorbed in reticulum and omasum
What are the main VFAs?
-acetate
-propionate
-butyrate
What are the characteristics of a high-fiber diet?
-higher acetate and lower propionate
-less total VFAs
-higher rumen pH
What are the characteristics of a high-starch diet?
-lower acetate and higher propionate
-more total VFAs
-lower rumen pH
What are the characteristics of protein fermentation?
-amino acids are deaminated by gut microbes
-produce ammonia and VFAs
-act as energy source for the synthesis of microbial proteins
Why is microbial protein synthesis important?
ruminants rely on it to meet their protein requirements
When is microbial protein production most efficient?
when growth rate of the microbial mass is maximized
Why is it important to have a balance of proteins and glucose?
to ensure proper energy for both protein synthesis & cell growth and cell maintenance
Which substrates can be used by rumen microbes to produce proteins besides other proteins?
-ammonia
-urea
-nitrates
What are the characteristics of urea recycling?
-hepatic urea originates from ammonia produced during protein metabolism by bacteria and the body
-urea can be secreted into urine or the rumen
What happens to urea in the rumen?
-converted into ammonia
-enters nitrogen pool for microbial synthesis
-allows ruminants to efficiently conserve protein and nitrogen
What are bypass proteins?
-proteins that pass through the forestomachs and into the intestine
-digested and absorbed in a similar fashion to monogastric proteins
What conditions are needed for optimal fermentation?
-adequate substrate provided
-appropriate temp., molality, and oxygen conc.
-removal of indigestible waste
-absorption of VFAs
-buffering of acidic pH
What is the path through the rumen?
-esophagus
-reticulorumen
-omasum
-abomasum
-duodenum
What are the layers of ingesta in the rumen?
-gas cap
-raft
-rumen liquors
What are the three main types of rumen contractions?
-mixing
-eructation
-regurgitation
What are the characteristics of mixing contractions?
-keep rumen contents well-mixed
-last 30-50 seconds
What are the characteristics of eructation contractions?
-allow for CO2 and methane build up in rumen to escape
-stretch receptors signal vagal afferents
What are the characteristics of bloat?
-obstruction in esophagus prevents gas eruption
-caused by diets high in saponins and/or grains that lead to dextrin slime production
What are the characteristics of regurgitation contractions?
-bring large particles into mouth for additional chewing
-initiated by presence of rumen raft
-stimulates saliva secretion
-occur every 2-3 minutes
How does diet type affect regurgitation?
-high grain diets have smaller particles and require less regurgitation
-high forage diets require more regurgitation
What are the characteristics of dilution rate?
-rate of liquid flow through the rumen
-% of total liquid leaving the rumen per hour
-must be replaced by more liquid
Why is a high fluid flow beneficial?
it washes away existing microbes and stimulates growth of new microbes
Which signals provide control over rumen motility?
-stretch/distension
-ingesta consistency
-pH
-VFA conc.
-ionic strength
How does raft size relate to rumen contractions?
-smaller rafts lead to less resistance to contraction and reduced muscle tension/motility
-larger rafts lead to more resistance to contraction and increased muscle tension/motility
What are the characteristics of pH?
-slightly acidic due to VFA production
-hyperacidity suppresses rumen motility
What are the main characteristics of hindgut fermentation?
-smaller particle size to start
-digestible carbohydrates and protein are already mostly absorbed
What are the functional segments of the hindgut fermenter’s colon?
-cecum
-ventral colon
-dorsal colon
-small colon
What is the goal of haustral segmentation motility?
promotes mixing and brings VFAs in contact with mucosa for absorption
What is the goal of propulsive peristalsis?
moving ingesta aborally
What are the functions of retropulsive peristalsis?
-retaining ingesta for more mixing
-allowing microbes to remain in colon instead of being flushed out
-allowing small particles to pass while retaining large particles
Where does retropulsive peristalsis occur?
distal left and distal right ventral colon
What is the pelvic flexure?
an area of narrowing in the distal left ventral colon that is prone to impactions
What are the characteristics of buffering?
-ileum secretes large amounts of bicarb. and phosphate buffers
-high VFA conc. stimulates water secretion by large intestine crypt cells
What is cecotrophy?
act in which hindgut fermenters consume fecal pellets for a “second chance” at the nutrients
