GI ruminants Flashcards
Definition of: Deglutiton
Swallowing
Definition of: Mastication
Chewing
Definition of: Regurgitation
• Passive transfer of stomach contents to oral cavity for re-mastication
Definition of: Re- mastication
• Additional chewing of fibrous material that has been regurgitated
Definition of: Rumination
• The entire process of regurgitation, re-mastication and re-deglutition (chewing the cud)
Definition of: Eructation
• Expulsion of gas from the stomach (belching / burping)
Definition of: Peristalsis
• Aboral movement of food down the GI tract by controlled contraction / relaxation of associated muscles
Definition of: Reverse peristalsis (anti peristalsis)
Aboral movement of food towards the mouth instead of away from the mouth
Ruminant stomach:
- Ruminant stomach adapted for fermentation of roughage / fibre
- 4 componetns. 3 parts = fermentation. 4th = stomach
- Enlargement of the oesophageal area = fore-stomach (3 compartments)
• Reticulum
• Rumen
• Omasum - Fourth compartment equivalent to simple stomach = Abomasum
Reticulum
- Inner surface raised into ridges (honey comb arrangement)
- Strongly muscled wall (smooth muscle)
- Capacity = 10-20 litres
RUMEN
- Longitudinal groove / pillar divides it into dorsal & ventral sac
- Coronary (vertical) grooves / pillars define caudo-dorsal / ventral blind sacs = slow fermentation
- Walls contain smooth muscle for contraction
- Papillae (especially caudo-dorsal blind / ventral sacs) – SA inc
- Absorption of (huge quantities of) H2O, VFAs, ions
- Papillae increase surface area for absorption
- No smooth muscle (immobile)
What compartments make up the fore stomach?
- reticulum
- rumen
- omasum
Why are reticulum and rumen often grouped together?
- functionally do same thing
2. very heavily involved with one another when it comes to motility
What is the nervous contribution to the rumen?
- regulate contraction via short reflexes of enteric nervous system
- modulated by long reflexes via vagus nerve
Histology of forestomach
- Stratified squamous epithelium
ABOMASUM
- “true” stomach
- columnar epithelium with glands that secrete: HCL, pepsinogen, rennin (in young ruminants)
- Receives small quantity of fermented material from omasum that contains lot of bacteria the abosasum can digest. REst = into small intestine
- pH slightly higher than simple stomach (2) of about 4 due to alkalinity of fermentation fluid. Still low enough to kill ruminal microbes for digestion
Why is renin secreted into the abomasum of young animals?
- Renin precipitates/ coagulates casin to stay in abomasum longer so pepsin more change to digest more efficiently
How are digestive components distributed in rumen reticulum?
- Distribution of forage in rumino-reticulum of grazers depends on density
- Very dense particles such as stones / wire fall straight into reticulum where they usually remain
- Density of other particles depends largely on associated gas from their fermentation
- Large particles (eg long grass / hay / straw) “float” in bottom of dorsal sac at level of oesophagus
- More dense particles sink into reticulum / cranio-dorsal blind sac / ventral sac – for absorption
- Gas from fermentation (CO2 / CH4 / H2S / H2 / N2) collects at top of dorsal sac
Rumino-reticulum motility
- 3 types of contractions
- Primary c
- Secondary c
- Rumination c
Talk about primary contractions of the rumino-reticulum
- Main one
- occur pretty continuously
- higher frequency when eating, lower when ruminating, very low but still occur when not eating
- point = move things around and mix up
What do the number of contractions tell us about a ruminant?
What is the “normal” number?
How healthy it is
Number:
1. Primary (mixing of contents)
• 5-8 strong contractions / 5 mins during eating
• 4-5 contractions / 5 mins during rumination
• 0-1 weak contractions / 5 mins during fasting (sleeping)
2. Secondary (eructation)
• Occur after every 2-3 primary contractions
3. Rumination (regurgitation / remastication / reswallowing)
Secondary contractions
POINT = get rid of waste gas
fairly frequently
gas out of front end
Rumination contractions
- contractions required to move material from rumen up oesophagus to mouth
Go through contractions from first reticular contraction
- primary: First reticular contraction (partial) moves coarse material towards central/ dorsal rumen
- Primary: Second reticular contraction (complete) moves material into:
a) cranial blind sac.
b) FERMENTED material = through reticulo-omasal orifice into omasum - primary: cranial blind sac contraction = moderately fermented material into dorsal sac. Well fermented material passes into reticulum
- primary: dorsal sac contraction = backwards contraction. Overall circular movement of contents in dorsal sac. some gas exchange with ventral sac
- Primary: Ventral sac contraction = backwards contraction
overall circular movement of contents. Some exchang with dorsal sac. Well fermented mat = into cranial blind sac
Contractions during rumination
- Rumination occurs when coarse material stimulates oesophageal opening
- An extra reticular contraction precedes the normal biphasic reticular contractions
- Normal primary contractions then follow
- Rumination occurs 6-10 times per day requiring approx 60 mins per kg roughage eaten
- Rumination generally occurs at night and during afternoon rest period
- Ruminants NEED to ruminate
Rumination: from mouth
- Newly swallowed material forced into dorsal sac and replaced by partially fermented material
- Thorax expands generating negative pressure in oesophagus
- Lower oesophageal sphincter opens
- Diaphragmatic muscle contractions forces material into oesophagus
- Cf abdominal contractions in vomiting
- Reverse peristaltic oesophageal contractions convey material to oral cavity
- Liquid immediately re-swallowed
- Rest of material re-chewed with additional salivary secretion & re-swallowed
Eructaiton contractions
- 2000-4000 litres gas from fermentation per day in dorsal sac
- Occurs after every 2-3 primary contractions
- Oesophageal opening usually below level of gas hence gas can’t escape during rumination
- Eructation can’t occur with animal lying on side
- Makes general anaesthesia / surgery complicated
Eructation
- Primary contractions occur as normal
- Caudo-dorsal blind sac contracts forward displacing contents into relaxed cranial blind sac and ventral sac
- Dorsal sac continues contracting and moves gas at top of dorsal sac to oesophageal opening
- Increased negative pressure in thorax causes oesophagus to expand
- Cardiac sphincter opens and gas escapes into oesophagus, reverse peristalsis carrying gas to oral cavity
- Some escapes via mouth but most inhaled (hence odorous substances sometimes getting into the milk)
- Ventral sac contraction allows gas collecting in caudo-ventral blind sac to escape to the top of the dorsal sac of the rumen
What causes bloat?
- Failure to eructate results in “bloat”
- Complete oesophageal obstruction eg potato
- Partial oesophageal obstruction eg neck abscess / tumour
- Fresh clover results in small bubbles that fail to coalesce, form a foam that doesn’t collect in the dorsal sac and hence can’t be eructated (“frothy bloat”)
- Increased ruminal pressure causes respiratory & cardiac distress
- Stretching of rumen reduces / stops ruminal contractions
How is the forestomach motility regulated?
- Occurs mainly by autonomic long reflexes
- Both afferent (sensory) & efferent (motor) fibres travel in vagus
- Vago-vagal reflex both vagal routes
- 2 types of sensory cell containing:
- Tension receptors – moderate stretching
- Both mechano (high stretching) & chemo-receptors
How is motility stimulated?
- Tension receptor containing cells
- In series with smooth muscle cells & sensitive to moderate stretch of rumen walls
- Concentrated around oesophageal opening, oesophageal groove, reticulum wall, rumen pillars & cranio-dorsal blind sac wall
- INCREASE motility
How is motility inhibited?
- Mechano- & Chemo-receptor containing cells
- Sensitive to severe stretch, pH, osmolarity & VFA concentration
- Located in basal layer of rumen epithelium (epithelial receptors)
- DECREASE motility (so animal metabolism can catch up)
Describe the development of the forestomach
- At birth abomasum developed but not fore-stomach
- Fore-stomach develops when starts to eat more roughage at about 2-3 weeks old
- Micro-organisms for fermentation develop too but still dependant on milk for nutrition
- Received mainly from mother by licking hence why bonding so important
- Milk bypasses fermentation chamber via oesophageal groove
What is the oesophageal groove
muscular structure at the lower end of the esophagus that, when closed, forms a tube allowing milk to go directly into the abomasum. (This prevents milk from being fermented or soured by the ruminal microorganisms)
- formed by posture of calf (lifting head to suckle)
- unconditioned reflex
- closes in diff species at diff ages when weaned
brief structure and what happens when drinks
- Groove with lips that runs from oesophagus to reticulo-omasal orifice
- When animal sucks warm milk reflex causes lips to curl over forming a tube
- Cold milk prevents complete curling over and can then spill into reticulo-rumen
What if bucket fed or milk intake exceeds capacity of tube ?
- Groove with lips that runs from oesophagus to reticulo-omasal orifice
- When animal sucks warm milk reflex causes lips to curl over forming a tube
- Cold milk prevents complete curling over and can then spill into reticulo-rumen
What stimulates closure of osophageal groove/ reticular groove or ventricular groove
- Sucking and chemoreceptors in pharynx sensitive to milk compounds cause reflex closure of groove
- Can also be stimulated by certain salt solutions used to prepare oral medication that bypasses fermentation chamber
Why deos fermentation occur?
- Most plant material cannot be digested by mammalian enzymes
- Requires microbial fermentation = chemical breakdown of a substance by micro-organisms under anaerobic conditions
• Rumino-reticulum
- Physiologically function together
- Provide environment for microbial population
- Delay gut-transit to allow sufficient time for fermentation
- Lignified roughage retained longer than succulent herbage
What does the bacteria Amylolytic do?
ferments hydrolysable carbohydrate
life span 0.5 hrs
What does the bacteria Cellulolytic do?
ferments non-hydrolysable carbohydrate
2. life span 18 hrs
What is an important condition and why?
- ANAEROBIC
• Under aerobic conditions food substances would be completely broken down to CO2 & H2O which don’t provide energy to the host
• Anaerobic conditions prevent total degradation resulting in metabolites that host can use for energy
What is the name for anaerobic bacteria that use O2
facultative anaerobes
Adhere to luminal surface
• Remove all O2 thereby rendering environment anaerobic
Describe microorganism set up in reticulum/rumen
- Most are bacteria
- Protozoa much larger therefore contribute almost equally to microbial mass
- Environment physically / chemically regulated
- Density and competitive balance between micro-organisms remains stable PROVIDED feeding pattern is stable
- Too rapid change in ingested food will upset balance
Microorganisms in the rumen/reticulum
- BActeria = amylolytic, cellulolytic proteolytic, methanogenic, lactate-utilisers
- protozoa
- fungi
How is the mcirobes established when the newly born gut is sterile?
• Microbes must be ingested (mostly from mother initially)
• environmental microbes ingested,
ruminal ones establish (competative advantage)
• Due to rumination mother’s oral cavity contains representative populations of ruminal microbes
• Transferred to young by licking / grooming
• This bonding therefore essential to establishing ruminal microbial population
What would ahppen if the neonate was isolate?
- gradually establish bacterial but not protozoal populations (protazoa can live long in open environment)
- fermentation will develop just not as efficient
How are bacteria classified?
on basis of nutrients metabolised
Protozoa
- Mostly ciliates, much larger than bacteria (can engulf bacteria)
- Retained longer in rumen by adhering to large feed particles
- Produce VFAs, lactate, CO2 & H2
- Proliferate with high starch diets, reduced with high fibre diets
- Store glucose as glycogen
- This glucose can be recovered when protozoa pass into small intestine and are digested
- Ruminants can survive without protozoa but fermentation much more efficient in their presence
Fungi
- Represent small proportion of microbial population
- Reproduce by free-swimming flagellated spores
- Can only break down lignin aerobically
- Rumen under anaerobic conditions!
- Lignin indigestible but presumed that spores attach to lignin and split it apart by hyphae thereby rendering it susceptible to celluloytic digestion
- Proliferate with diets high in lignin (e.g. straw)
RUMEN ACIDOSIS
- Consumption of increased levels of hydrolysable CHO
- VFAs ↑↑ / pH ↓↓ (amylolytic survive, cellulolytic don’t protozoa die LP inc)
- If pH decreases too much acid-resistant lactate producers proliferate at expense of lactate-utilisers
- Lactate poorly absorbed cf VFAs
- Too low pH injures rumen epithelium
- Water enters rumen by osmosis inc in solutes but now can’t reabsorb water = blood vol dec
- Dehydration / hypovolaemic shock ensues
- Treated by iv alkaline fluids (corrects both dehydration and acidosis)
- Can be prevented by introducing levels of hCHO gradually (over 3-4 weeks) to enable lactate-utilisers (cant work at low pH) to increase in level with lactate producers
Why is it important not to change the diet of a ruminant rapidly?
- important not to disturb the ratio of diff families of microorgansims? bac, protozoa and fungi
- Quickly = upsets one populaiton at expense of other
- usually myolytic (rapid fermenters) tend to be more resistent
- inc rate of fermentation = produce VFA at faster rate than designed = decrease pH
Role of amylolytic bacteria
- break down alpha glycosidic bonds = hydrolysable carbo
- survive low pH
- proliferate v quickly = can get out of hand if upset environ
Role of cellulolytic bacteria
- break down non hydrolysable carbo (beta glycosidic bonds)
2. can’t survive at low pH = die if envir disturbed
Role of proteolytic bacteria
- fermentation of protein and then use for themselves
2. protein –> peptides –> aa –> VFA and NH4+
Role of methanogenic bacteria
CO2 into CH4
small proportion
Role of lactate utilisers
lactate –> propionate
die at low pH
as protein is digested what is produces?
As CHO digested what produced?
- NH4+
- VFA
- pH DOWN
Homeostasis of rumen
- digestion = NH4+ and VFA inc
- pH dec which inc osmoregularity
- water enters rumen by osmosis
- NH4+ taken up by microbes, VFA absorbed by host
- Increased rumination/ HCO3- from saliva and blood
- osmoregulatily dec, pH inc
- water reabsorbed
Ruminant metabolism
- V efficient, only 10% feed energy lost (mostly via CH4 production)
- Rumen microbes can degrade many toxins before their absorption cf simple stomached animals
• Foxglove leaves (digitalis)
• Ragwort (horses v. susceptible - Homeostatic envir must be maintained
What is the rate of fermentation in the ruminant dependent on?
- Type of feedstuff
• Starch fermented more rapidly than fibre - Volume of feedstuff
- Microbial balance
• Amylolytic bacteria ferment faster than celluloytic
How is propionate formed?
- via 2 metabollic pathways
• Via anaerobic glycolysis of pyruvate
• From lactate - diet high in starch enable proliferation of lactate utilisers so inc overall VFA production :. inc relative propionate production
Methane production
- need to be produced
- for glycolysis to occur need to reduce NAD+ to NADH
- Methane producers reduce CO2 to methane via oxidation of NADH back to NAD+
- regenerated NAD+ and recyled H+ ions thereby help maintain ideal rumen pH
Methane production
- need to be produced
- for glycolysis to occur need to reduce NAD+ to NADH
- Methane producers reduce CO2 to methane via oxidation of NADH back to NAD+
- regenerated NAD+ and recycled H+ ions thereby help maintain ideal rumen pH
How does a ruminant metabolise fat
- diets modified to inc fat especially in dairy cattle
2. hydrolysed and fermented to VFAs
How does a ruminant metabolise protein
- again not directly availabel to hsot but to bacteria
- Degraded into peptides, AA, Nh3 and organis acids and branches fatty acids (stimulate growth of cellulotic bacteria)
- for microbes to proliferate = high rate of protein synthesis
Where do microbes get nitrogen from for protein synthesis?
- Most = inorganic nitrogen
2. also non protein nitrogen in food and additives (urea)
Metabolism of NPN
- what are NPN
- NPN consist of amides, amines, peptides, amino acids, nucleic acids, urea, nitrates & ammonium ions
- Ruminants (cf other simple-stomached animals) can utilise NPN for protein synthesis (via microbes)
- NPN → NH3 → amino acids → protein
- Microbial protein digested in stomach / small intestine as in simple-stomached animals
- NPN essential for healthy microbial population
- Grass / grain contains 5-15% NPN
- Silage (due to microbial fermentation) contains 70% NPN
Why silage fed? esp dairy cows
- partly fermented so contains 70% NPN vs grass 5-15%
What lactation requires
- dairy dcows require more than microbial protein
- urea often added to inc NPN to inc microbial population
- inc microbial proliferation = inc VFA to host. Molasses = good source
- Xtra by pass protein added to diets escape fermentation as poorly soluble and pass into abomasum. small I for digestion
What is unique to ruminants with surplus protein?
- recycled into urea by liver and secreted in saliva
Waht is absorption?
What enhances absorption in ruminant?
- selective transfer of useful nutrients into the hosts blood stream
- • Reticulo-rumen enhances this by papillae that increase surface area for absorption
• Papillae most dense in parts of rumen responsible for absorption (ventral sac & cranial / caudo-dorsal blind sacs). absorbs principially VFA
Omasal absorption
smaller component – regulates passage and mops up water
• Surface area increased by leaves / papillae
• Fermentation continues in omasum
• Absorption of ~10% total VFA leaving only ~10% passing into abomasum
• Water (10-15%) / Na+ (25%) also absorbed
• Ingesta therefore more solid than in rumen
• Contains less HCO3- therefore abomasum needs to secrete less H+
• Some rumen material passes straight into abomasum via omasal canal
