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Review - Ruminant Digestion

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sihirlifil's version from 2018-02-06 14:33

Anat & Phys

Question Answer
How does fermentation differ from glandular digestion?FERMENTATION: digestion occurs by microbial enzymes
GLANDULAR: enzymes are from host animal
What happens in the rumen?Fermentation
Conditions that favor fermentation (4)Anaerobic environment
Slow rate of passage
Neutral pH (6-7)
Approximate T = 37*C (body temp lol)
Rumen microenvironment is made up of (3)Bacteria
Protozoa
Fungi
What are the rumen bacteria like?28+ functionally important species that we know if (>200 total), with most species dependent on others
Obilgate anaerobes and some facultative anaerobes
*How are facultative anaerobic rumen bacteria helpful?They can take up any O2 that happens to get in there & protect the obligate anaerobes
What are the rumen protozoa like?>40 species, most anaerobes
Not essential to fermentationbut necessary to keep bact #s in check
What's the role of fungi in the rumen?Unknown
The rumen can adapt rapidly due toShort generation time (of microenvironment)
___ are the main nutrients that undergo fermentationCarbohydrates
Carbohydrates are broken down by what? Into what?Extracellular microbial enzymes --> glucose, monosaccharides, short-chain polysaccharides
CHO fermentation: what happens when sugars are taken into microbial cells?Produce pyruvate via glycolysis --> generate NADH & ATP
CHO fermentation: after pyruvate is produced by glycolysis, what happens?Reduced into VFAs: Acetate, proprionate, butyrate
Acetate/proprionate/butyrate ratio varies based onDiet
Microbial waste products of fermentationVolatile fatty acids & methane
VFAs are important becauseGlucose never reaches site of glandular digestion (abomasum)
Ruminants are in constant 'glucose deficiency'
Most important VFA for gluconeogenesis?Proprionate (acetate & butyrate?)
Major source of nutrition for ruminants:VFAs
Where are VFAs absorbedRumen epithelium (papillae)
How does absorption act as a buffering mechanism?Prevents accumulation of VFAs & resultant pH shift
Causes secretion of bicarb into rumen
Growth of rumen papillae stimulated by?VFAs! High digestibility --> more VFAs --> longer paipillae
Dont shift to high grain diet suddenly!
T/F Glucose fluctuates more in ruminants than in other speciesF! And normal range is much lower (40-60 mg/dL)
Reduced due to constant 1) eating 2) VFA production 3) outflow of digesta from rumen 4) gluconeogenesis
How is rumen motility controlled?Gastric center of medulla
Impulses result in rumen contraction
Rumen motility (motor) is depressed by:Catecholamines
Anesthetics
Endotoxemia
Rumen motor impulses impaired by:Hypocalcemia
Botulism
Inhibitors (sensory) of rumen motility?High-threshold stretch receptors (slows down to give time to ferment)
Abomasal tension receptors (prevents overload)
VFA receptors in rumen wall (stays in fiber mat until VFAs go down)
Splanchnic pain
Excitatory impulses (sensory) of rumen motility?Low-threshold reticular threshold receptors (contraction stims regurg)
Buccal receptors
Abomasal acid receptors
Scratch factor
4 phases of cycle ruminationRegurgitation (brings up cud into mouth)
Remastication (chews food)
Reinsalivation (saliva buffers the food)
Reswallowing (chewd food goes back down)
Function of ruminationRapid ingestion of feed while foraging or grazing, then complete chewing at a later time
Rumen zones (pic)Linear stratification of water, fiber, and gas
Describe primary rumen contractionSeparates large & small particles
Biphasic contraction of reticulum
Dorsal & ventral sacs
1 per minute
Describe secondary rumen contractionPushes gas to cardia (eructation)
Dorsal sac only
Follws 2 primary contractions
When does regurgitation occur? what happens?Occurs before 1ry rumen contraction
Inspiratory excursion --> food bolus into esophagus --> tongues squeezes water --> Remastication
Time spent ruminating varies withDiet! 0h/day on high grain diet, 10h/day on high forate
Rumination is greater with (higher/lower) dry matter intakeHigher
Until what point does feed stay in rumen?Particle size decreases (10-20mm in dorsal rumen, 2-3mm in ventral)
Which kind of fiber remains in rumen longer?Poorly digestible (30 hours for high, 50 hours for poor)
Rumen development: calves are considered non-ruminant at what age?0-3 weeks
Rumen development: calves are in the transitional stage at what age?3-8 weeks
Rumen developemnt: when can calves eat grain/forage?By 2 weeks!
Rument development: calves can ruminate by what age?3 weeks (said in class: if pushed, like couldnt get colostrum from dam for some reason etc)
How does the rumen develop more quickly?If exposed to solid feed
Rumen development: without solid feed, reticulorumen can remain rudimentary at what age14-15 weeks
Rumen development: what do grains do?Stimulate VFA production --> increased epithelial development
Rumen development: what does forage do?Stimulates rumen wall muscular development
What is the forestomach like at birth? What has to happen after?STERILE at birth. Environmental bacteria colonize, but inoculation with protozoa requires presence of other cattle
Sources of water intakeDrinking, salivation, feed
What is water flow like?Water is continually exiting reticulum, and rarely flows from vascular space into rumen (exception: grain overload)
How much saliva produced per day? contains what?200L/d
High concentrations of bicarbonate & phosphorous (buffer!!!)
Whats the function of the reticulum?Aids in regurgitation of cud
Anatomy of reticulumMost cranial & ventral component (next to dipahragm, collects hardware!!!)
Honeycomb (no secretions)
Esophageal groove: formed by what?Tunnel between cardia & omasal canal
Function of esophageal grooveAllows liquid to bypass rumen --> Divers to abomasum for milk digestion
Activity of reflex decreases with age (more rapid absorption of water in small intestines)
How can we stimulate the esophageal groove reflex in adults?ADH
How is the esophageal groove controlled?Suckling AND milk proteins! Milk, colostrum and ilk replacer bypass the rumen, but water still enters rumen
Forms whether calves drink from a nipple or an open bucket
What's this?
Esophageal groove
Describe the omasumConsists of body & canal
Body consists of leaves (project from greater curvature into lumen)
Canal is located at lesser curvature
Function of omasum?Incompletely understood... large mucosal surface area so maybe removal of residual VFAs & bicarb
Abomasum =Glandular componenet ("true" stomach)
What happens to pH in the abomasum? important why?Decreases from 6 to 2.5
Denatures proteins, kills pathogens, dissolves minerals, glandular digestion
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PE & Lab

Question Answer
How can we assess the rumen? (4)Abdominal contour (& ballottement)
Rumen motility (feel contractions)
Rectal exam
Lab eval
Different abdominal profiles:Paralumbar distension
Ventral abdominal distension
"Papple"
Abdominal profile:
Paralumbar distension
Abdominal profile:
Papple (L-shaped rumen)
How many rumen contractions/min? sounds like?2-3 per 3 minutes
Sounds like ocean... or avalanche
Where do you auscult rumen contractions?LEFT paralumbar fossa
Whats the rectal exam for?Assess rumen fill: ingesta, gas cap
Examine feces
Rectal exam: feces should be likeNot smell sour
Big pieces of fiber should not be present
Look for blood/melena
Lab exam: what are you collecting? how?Collect rumen fluid via orogastric tube (requires Frick speculum) or percutaneous ruminocentesis
What's the difference between orogastric tube & percutaneous rumenocentesis?
Rumen fluid analysis: color?Depends on diet (olive green, yellow, brown)
Black-green = rumen stasis
Milky gray-brown = lactic acidosis
Rumen fluid analysis: odor?Normal: slightly aromatic
Lactic acidosis: acidic/sour smell
Putrefaction: rotton odor
Rumen fluid analysis: consistency?Normal: slightly viscous
Rumen fluid analysis: sedimentation?takes >5 min to settle
Fluid pH >8 =Saliva contamination
Fluid pH 7-8 =Anorexic
Fluid pH 6-7 =Normal
Fluid pH 5.5-6.5 =70% grain diets
Fluid pH 4-5 =95% grain diets
Fluid pH <4 =Acute grain overload
Rumen fluid analysis: protozoa?Normal: >40 per LPF
Should be highly motile
How do you handle a rumen fluid sample?Keep warm & O2-free until eval
Rumen fluid analysis: Cl-?Norm <30 mEq/L
What happens to cholide with abomasal/SI obstx?**<45: impaired outflow >45 owtflow obstruction
Explain the New Methylene Blue reductionMeasures redox potential: estimate of anaerobic microbial function
20 parts rumen fluid: 1 part 0.03% NMB
Normal <5 min
What should gram stain of rumen fluid be?90% G-
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