Lecture 27: Forestomach Motility Flashcards
What are the 3 things create a favorable environment for microbial fermentation
- Continuous substrate supply
- Appropriate and constant temperature, sufficient time and space, pH control
- Removal of indigestible waste, microbes, VFA
What 2 components facilitate selective retention
- Specific forestomach morphology
- Motility patterns
What is selective retention
Retain actively fermented material and remove waste
What type of epithelium is in the forestomach
Stratified squamous
What are the 3 surface extensions throughout the forestomach
- Honeycomb folds in reticulum
- Rumen papillae
- Omasal laminae
What is the purpose of the surface extensions
Increase surface area to retain VFA, electrolytes, water to be absorbed in rumen and omasum
What separates the cranial and ventral sac of the rumen
Cranial pillar
What connects the omasum to the reticulum
Reticulo-omasum orifice
What are the 3 motility patterns of reticulum and rumen
- Mixing
- Eructation
- Rumination
What happens during mixing pattern
Reticulum and rumen facilitate mixing via contraction cycle
What is the contraction cycle in the mixing pattern
- 1st recticular contraction mixes fresh material to send to rumen
- Contraction of the cranial pillar and reticulum moves food to dorsal sac
- Dorsal sac contracts followed by ventral sac
- Ventral sac contracts and cranial pillar relaxes and moves dense material to reticulum
- Second reticular contraction evacuates dense particles through ROO
What happens to the non-sedmented material, small particles that do not move through ROO
Regurgitated as cud
Describe the path of a single bolus
- Initial chewing and some mechanical/mastication and chemical breakdown with
- Ingesta arrives in reticulum and transported via mixing contractions to rumen
- Ventral caudal sac spills material with smallest particles to cranial ventral sac to reticulum
- Reticulum contraction forces material through ROO to omasum
- 1-3 cycles per minute
How do contraction cycles change during feeding
Increase
lower during resting
What is eructation
Removal of gases
Describe the process of eructation
- Cranial pillar remains solid and retains solid digesta in rumen
- Dorsal sac contracts caudal to cranial and moves gas cap forward
- Reticulum and cranial sac relax and
- Cardia opens and gas enters esophagus
- Ventral sac contracts and cranial pillar relaxes to move dense material into cranial sac and secondary contraction cycle concludes
What is rumination
Reduction of particle size via mastication and salivation
What are the 4 important components of rumination
- Regurgitation
- Mastication
- Salivation
- Deglutition
How does mastication help in rumination
- Breaks down cell wall and structures making it easily digestible
- Stimulates saliva production
How does regurgitation occur
- LES/cardia relaxes
- Inspiratory excursion of thorax
- Glottis remains closed
- Reversed esophageal peristalsis
Why do ruminants always rest in sternal recumbency
To maintain layer structure of rumen which is essential for normal motility and removal of gas cap
Need gravity for floatation and sedimentation of rumen digesta
What is the normal layering in the rumen
- Gas cap on top
- Fiber mat floating on water layer
- High density sedimented material
Why does unfermented and digestible material float
Plants contain lots of air that makes them less dense
What separates the sediments and floating fiber mat
Liquid layer
How are the different layers in the rumen content generated
Different material density
Where is the largest microbial activity in the rumen and why
Boundary between fiber mat and water layer because microbes prefer a more anaerobic area
What is bloat
Form of indigestion marked by excessive accumulation of gas in rumen
Bloat is a failure of what
To clear cardia due to foaming ingesta, foaming prevents typical layer structure ingesta in rumen
What does bloat due to respiratory rate, heart rate and organ perfusion
Decreases respiratory rate because compressing diaphragm, decrease HR and decrease organ perfusion
What determines particle size and its reduction rate
Digestibility, microbial action, mastication and physical properties of ingesta
Break down of poorly digestible fibers takes __
Longer
Rumen volume is limited therefore intake rate can’t exceed ___
Outflow rate
Poorly digestible feed takes longer/has longer ___ and is associated with ___intake
Transit time and is associated with less intake
Would grinding poorly digestible fiber increase dry matter intake
Yes temporarily but VFA and lactate production will increase, decreasing pH which provides advantage to lactate producing bacteria but disadvantages to cellulolytic, hemicelulolytic and pectinolytic species
How does increase VFA affect activity of microbes
Negatively impacts because microbial enzymes require certain pKa’s to function so decrease pH can decrease their activity
How does the rapid passage of feed affect VFA production
Reduces
How does smaller particle size influence mastication and saliva
Requires less mastication and therefore less saliva produced, which means less water, buffer, and urea via saliva provided to the rumen
Acidosis
What determines dilution rate
Water influx to the rumen
What are the sources of water to the rumen
Drinking, saliva, water in feed
What does saliva production depend on
Chewing time and feed type
How does a high roughage diet affect mastication and saliva
Increases both
How does a highly digestible feed affect mastication and saliva
Decreases both
Water is importantly for __sorting, __ and transport of solids and ___yield from rumen to omasum
Particle sorting, fermentation, and microbial yield
A __ dilution rate would cause more rapid removal of microbes
Higher
A higher dilution rate can stimulate __growth if sufficient substrate is available
Microbial
Microbial action of ___ bacteria would be reduced as a result of paid passage of fluid
wanted bacteria like VFA producing
Dilution rate can positively and negatively affect ___ production and ___ yield
VFA production and microbial yield
Is there a sequence of cephalic, gastric, and intestinal phase of secretion in ruminants
No because digesta flows continuously from rumen to abomasum which is associated with continuous secretion from stomach and pancreas and saliva production
What PNS nerve controls motility
Vagus
What do afferent signals/receptors communicate about motility
Distention, ingesta, consistency, pH, VFA, concentration, ionic strength
What nucleus in brain is necessary for normal motility
Dorsal motor nucelus
Where are motility stretch receptors located
Wall and pillar of rumen
How do stretch receptors control motility
Moderate distention causes increase motility
How do stretch receptors respond to severe distention like bloat
Can’t compensate, insufficient force produced by rumen wall
How do tension receptors control motility
Measure tension force generated by rumen wall muscles. Rumen mat provides different resistance
What is the normal rumen pH
5.5-6.8
How do VFA’s affect motility
Decrease pH which reduces motility
How do chemoreceptors control motility
Sense pH which is decreased by VFA’s and motility is reduced, this helps slow down fermentation until enough material is removed from rumen
How do chemoreceptors work in abomasum
Senses pH drop below 2-3 which stimulates rumen motility to advance waste to omasum.
Feedback mechanism from abomasum to rumen o signal that more food can be digested to abomasum
Afferent signals from ___ and __ nerve affect motility and generate normal motility patterns
Dorsal motor nucleus and vagus nerve
What is Hoflund syndrome
Damage to the vagal innervation removes or causes erratic motility patterns
Fatal
What is reticuloperitonitis
Aka hardware disease
Sharp object trapped in reticulum and contractions can cause object to penetrate through reticulum wall causing leakage of ingesta and bacteria into peritoneal cavity
How can we treat reticuloperitonitis
Use magnets to trap objects
