The rumen (anatomy, microbiology, function, diseases) Flashcards
Name the digestive sacs of the ruminant
- Rumen
- Reticulum
- Omasum
- Abomasum (true stomach)
What is the function of the rumen-reticulum?
- Mammals unable to digest beta-linked polysaccharides e.g. cellulose
- Rumen reticulum (and omasum) allows utilisation of micro-organisms to assist digestion
- Rumen is large fermentation vessel
Give a brief overview of the forestomachs of the ruminant
- Rumen, reticulum, omasum
- Derived from gastric spindle
- Lined by stritified keratinied epithelium
Give a brief overview of the ruminant abomasum
- “True stomach”
- Analogous to stomach of monogastrics
- Acid producing
- Lined by simple columnar epithelium with occasional goblet cells
Where is the rumen-reticulum located?
Takes up most of left side of abdominal wall
Name the sacs of the rumen (in order, starting at the top going clockwise)
- Dorsal sac
- Dorso-caudal (blind) sac
- Ventro-caudal (blind) sac
- Ventral sac
- Cranio-dorsal (blind) sac
(At very front have reticulum, kind of like sac of rumen)
Where are the omasum and abomasum located?
On the right side, omasum more cranial
Describe the oesophagus of the ruminant
- Large (diameter up to 6cm)
- Distensible
- Striated m. along whole length
- Mucosa insensitive
What is “chock” and where does it comonly occur?
- Obstruction of oesophagus
- Commonly close to pharynx and at thoracic inlet
Describe the conditions in the rumen-reticulum and why this is important
- Large volume
- Warm (close to body temp)
- Moist
- Anaerobic
- pH ~6.5
- Environment suitable for range of microorganisms that digest and degrade plant material
- Particularly cellulose and hemicellulose
What are the products of fermentation in the rumen?
- Volatile fatty acids (acetate, butyrate, proprionate)
- CO2
- Methane
- Fibrous feedstuffs remain long enough for complex carb digestions
How frequently do rumen- reticulo contractions occur?
~3 every 2 mins
What is the purpose of the rumen-reticulo contractions?
- Stire, redistribute and mechanically grind food
- Partitions fibre for re-chewing
What are the layers of digestive material found in the rumen-reticulum? (top to bottom)
- Gas
- Fibre mat (thickest fibre material)
- Intermediate zone
- Liquid zone
What are the fates of the rumen-reticulo zones?
- Fibre mat selected for remastication
- Liquid zone moves forward into omasum and abomasum
What is the function of the cycling movement in the rumen-reticulum?
- Stirs and redistributes contents
- Maximises efficiency of breakdown, eructation, remastication and forward movement of digested food
What are the 2 types of cycles found in the rumen-reticulum?
- Primary (A) cycles
- Secondary (B) cycles
Describe the primary (A) cycles within the rumen-reticulum
- Mixing
- every 1-2 mins
- Diphasic contraction of reticulum - monophasic contractino of dorsal sac then ventral sac
Contraction wave moves in cranial to caudal direction - Mix ingesta and aids flow of liquid layer into omasum
Describe the secondary (B) cycles within the rumen-reticulum
- Eructation cycles
- Every 1-2 mins
- Result in erucation
- Rumen dorsal wall contraction then ventral sac contraction
- displaces gas into cardia, leads to eructation assisted by anti-peristaltiv wave
- Most gas first inspired before being released
- Primary and secondary contractions independent
Describe process of regurgitation in the ruminant
- Additional contraction
- Reticular contraction floods cardia
- Inspiratory effort, closed upper airway, expands thorax, reduce pressure in thorax and expanding oesophagus
- lower oesophageal sphincter opens, material propelled forward by abdominal effort
- Antiperistaltic wave in oesophagus transfers bolus to mouth
- Liquid component reswallowed and fibre component masticated approx 50 more times before being swallowed
- occurs between primary cycles
- Occupies 6-12 hours per day depending on diet
Describe how the rumen-reticulo contractions are regulated
- Integration centre in brainstem
- Sensory cells in forestomach - info via vagal nerves
- Stretch sensitive, mechano and chemoreceptors (stretch, pH, osmolarity, VFA concentration)
- Motor supply via vagal nerve
- vago-vagal reflex
Breifly outline the structure of the omasum
- Broadly spherical, slightly flatterned sides
- Approx 100 laminae, covered with conical papillae, increase SA
- Relatively smaller in sheep and goats
- Curtained appearance
Briefly outline the function of the omasum
- Function unclear
- Possible water absorption
- Regular biphasic contractions, squeeze material into recesses and tehn general contraction progresses fluid forward
Briefly outline the structure of the abomasum
- Similar to monogastric structure
- fundus, body (corpus), pylorus
- Larger in sheep and goats
- A dozen large folds
- Columnar epithelium
Glands producing mucus, pepsinogen, HCl - pH ~ 3-4
Briefly outline the function of the abomasum
- Similar to monogastric function
- Protein digestion in ruminants (can occur in rumen-reticulum and abomasum)
- Weak rhythmical contractions
Describe the appearance of the wall of the rumen
Covered in papillae (sheet)
Describe the appearance of the wall of the reticulum
Hexagonal shapes, papillae
How is the development of papillae in the rumen related to diet?
- Vary in shape and size depending on diet, age and location
- High concentration of VFAs (esp butyrate) promote growth
- Take time to adapt to dietary changes
What is the oesophageal groove reflex also known as?
The reticular groove reflex
Give a basic overview of the digestion of milk in the abomasum
- Milk digested in abomasum
- Fundic glands produce rennin
- Rennin coagulates casein milk protein) in acidic environments
- Clot retains milk to allow complete digestion by pepsin
What happens to milk in the rumen?
Ferments, causing scour and digestive upsets
What is the function of the reticular groove reflex?
Prevents milk entering the rumen and thus reduces the risk of scour
Describe how the oesophageal groove reflex works
- Directs milk from oesophagus into amasal canal and onwards to abomasum
- When stimulated, groove contracts
- Forms closed tube
What is the reticular groove reflex stimulated by?
- Suckling milk
- Feeding routine in artificailly reared calves
How is the reticular groove reflex “turned off”?
- After birth, forestomach starts to grow and develop
- Promoted by presence of forage in rumen
- Is becuase young animal starts to pick at solid food
- Rumen flora develops within a couple of weeks of birth
- By time animals weaned, forestomach capable of digesting adult diet
What is the significance of stomach tubing lambs and calves?
Can easily flood rumen with milk
Not catastrophic but does not acheive aim
Describe the bacterial flora of the rumen and related chambers
- more than 200 species
- Most non spore-forming anaerobes
- No host specificity
Descibe the fungal flora of the rumen and related chambers
- Strict anaerobes
- Motile zoospore phase, vegetative sporangium phase
- In vegetative found attached to food particles which penetrate pant cell walls
- Gennus Neocallimastix
- 12 species
- Digest plant material by secretion of enzymes
- Mechanical effect on structure as forms hyphae within material
- can utilise polysaccharides (cellulose), sugars, carbohyrates but not all
- Colones plant fragments in rumen of cattle and sheep on high fibre diets
- Actively ferment cellulose, resulting in generation of mixture of products
Describe the protozoal flora of the rumen and related chambers
- More than 100 species
- Most ciliates
- 2 families - Isotrichidae (holotrichs), Ophryoscolecidae
- Single celled eukaryotes
- Can be predators for unicellular or filamentous algae, bacteria, microfungi
- Control bacterial population and biomass
- Good indicators of rumen health
- Pick up from other animals (or parents)
- sensitive to low pH
- Each genus has specific effect on rumen fermentation
- Absence does not adversely affect animal
- Absence can be beneficial under certain dietary conditions
What is used by the rumen microbes?
- Proteins
- Sugar, acid, lipid
- Nitrogen
What is produced by the rumen microbes?
- Methane
- Carbon dioxide
- cofactors and metabolic intermediates (vit B12, aromatic growth factors, interspecies hydrogen transfer)
- cytochrome synthesis
What is produced by the rumen microbes?
- Methane
- Carbon dioxide
- cofactors and metabolic intermediates (vit B12, aromatic growth factors, interspecies hydrogen transfer)
- cytochrome synthesis
Describe the Isotrichidae family of protozoa
- Ovoid organisms
- Covered in cilia
- Include genera: Isotricha, Dasytricha
Describe the Ophryoscolecidae family of protozoa
- Vary in size and shape
- Cannot utilise cellulose
- Include genera: Entodinium, Diplodinium, Epidinium, Ophryoscolex
What is produced by fungi in teh fermentation of cellulose?
- Acetate
- Lactate
- Ethanol
- Formate
- Succinate
- CO2
- H2
Describe the neocallimastix life cycle
- Zoospore encysts and germinates
- Growth by digestion of material
- Sporangium develops
- Release of new spores
Describe the neocallimastix life cycle
- Zoospore encysts and germinates
- Growth by digestion of material
- Sporangium develops
- Release of new spores
What are the benefits of microbial fermentation?
- High quality protein from poor material
- Vertebrates cannot synthesise essential amino acids, mixture of fermentative microbes can synthesise all
- Synthesis of protein from non-protein nitrogen sources (urea)
- can produce all B vitamins (only 2 synthesised in mammals)
Explain how and why pH is maintained with relation to rumen microflora
- Acid (VFA) production can lower pH
- Buffered at 5.5-6.5 by phosphate bicarbonate buffer from saliva
- rapid absorption of VFAs and ammonia keeps effects low
- Prevents denaturing of microflora
Explain how and why the redox potential is maintained with relation to rumen microflora
- oxygen enters with food
- Rapidly soaked up by bacterial population
- Anaerobic conditions maintained, redox kept low
- ideal conditions for microflora
What are somethings that can cause disruption to the rumen microflora?
- Acidosis (rapid change to concentrate diet, more neat sugars)
- Cariation in diet (allow 2 weeks to cahnge microflora, diurnal changes, almost batch)
- Starvation
- Antibiotic therapy (may destroy rumen microflora)
- Attachment flow of microorganisms in rumen
Describe how rumen synchronicity can be maintained
- Some constituents of feed metabolised quickly, others slowly
- Balancing of feed will reduce fluctuations in nutrition and imbalances as microbiota adjusts
- Well balanced feeds can increase efficiency of rumen fermentation
- Feed will affect balance in what is produced
List the features that permit continuous fermentation in ruminants
- Anaerobic environment of rumen
- Constant temperature and pH
- Good mixing
- Well masticated substrates ]
- Huge fermentation vessel
- Many long meals throughout the day
- Microflora continuously moved into omasum, abomasum and SI
- Rumination means digestion continues after grazing is done
What direction do the rumen contractions go?
Cranial to caudal
How are the rumen contractions in the camelid different to those in ruminants?
- Ruminant go cranial to caudal
- Camelid go C2 for 2 mins, C1 for 8 contractions backwards and forwards, back to C2
What are the 3 oesophageal diverticula of camelids?
- C1
- C2
- C3
Describe the C1 oesophageal diverticulum of camelids
- Occupies large portion of left side of barrel
- Primary bacterial breakdown of plant cellulose
- Divided into cranail and caudal sac
- Ingeta homogenous
- Caudal and upper dorsal part of cranail sac drier
- Finer matter in lower ventral part of cranial sac
- Cud regurgitated from here
- ure a cycling
- Communicates with C2
Describe the C2 oesophageal diverticulum of camelids
- Sits on right abdominal wall
- Smaller than C1
- Liquid ingesta from C
- Dorsal lesser vurvature, ventral greater curvature
- Empties into C3 via short, thick-walled muscular tube
- Control rate at which meterial moves into C3
Describe the C3 oesophageal diverticulum of camelids
- Below C2
- Elongated
- Lower right abdo wall
- Last 1/5 contains gastric glands = true stomach
- Initial 4/5 lined by mucinous glandular mucosa
- Empties into diated ampulla delineating beginning of small intestine
What are some of the physiological differences between ruminants fed on diet of only roughage and diet of mostly concentrate?
- More regurgitation on roughage based
- More bacteria as wider variety of materials in food (roughage)
- Less secretion and not as much dilation of stomach (concentrate)
What are some of the biochemical differences between ruminants fed on diet of only roughage and diet of mostly concentrate?
High concentrate iet can lead to acidosis
Why do ruminants not need a dietary source of nutritionally essential amino acids?
- Are produced by rumen microflora which are “ingested” by the ruminant
What types of amino acids do ruminants consume?
- Non-essential
- Can be split into rumen undegradable and rumen degradable
What are the fates of rumen degradable and undegradable protein?
- Undegradable sent straight to rumen and abomasum
- Rumen degradable digested by microflora
Explain the role of microflora in protein digestion
- Rumen degradable proteins digested by microflora
- used to make microbial protein as population grows
- Also requires source of energy
- Vast quantities of rumen microflora flow into omasum and abomasum
- Ruminant digest microflora
- Good source of protein to ruminant
- Microbes can also utilise ammonia to produce microbial protein
Explain what is meant by “protein cycling” in ruminants
- Ammonia used by microbes o form microbial protein
- Excess ammonia to liver, used to make urea
- Most urea excreted, some recycled to salivary glands
- Swallowed in saliva
- Used to make microbial protein
List the products of carbohydrate digestion
- Carbon dioxide
- Methane
- VFAs (acetate, butyrate, proprionate)
- Pyruvate
What is the impact of overfeeding non-protein nitrogen?
- Increases blood levels of ammonia
- Liver overwhelmed
- Toxic levels in circulation
What is the impact of a high roughage diet?
- Produces more acetate
- Is precursor of milk fat
- If want high milk fat then feed low yielding cows more roughage
What is the impact of a high concentrate diet?
- Easy to break down
- Utilises lactate pathway to produce lots of proprionate
- Can lead to acidosis
- Chronic and acute acidosis
Briefly outline chronic acidosis
- more common
- High producing animals fed high concentrate diets
- Suboptimal rumen function
- Microflora constantly exposed to low pH
- leads to reduced food intake, pain, indigestion, loose faeces, low milk fats
Briefly outline acute acidosis
- Usually result of “grain engorgement”
- Break into feed store and eat as much as possible
- Rapidly fatal
- Water absorbed into rumen, hyppovolemic shock
- Surgically remove carbs from rumen
Describe carbohydrate digestion in the ruminant
- Complex carbs borken down to simple sugars using extracellular enzymes of rumen microflora
- beta-linked carbs (cellulose) digest by bacteria (mostly)
- Attach closely to food particles
- Simple sugars taken up rapidly by microflora and metabolised intracellularly to VFAs - anaerobic
- Also produces pyruvate by glycolysis
Briefly describe the production of VFAs in the rumen
- Breakdown of carbs
- Pyruvate intermediate step
- VFAs - acetate, butyrate, proprionate
- Excreted by baceria as waste products, used by ruminant
Outline the steps form pyruvate to acetate
Pyruvate -> acetyl phosphate -> acetate
Outline the steps from pyruvate to butyrate
Pyruvate -> acetyl CoA -> acetoacetyl CoA -> beta-hydroxybutyryl CoA -> crotonyl CoA -> Butyryl CoA -> butyrate
How many pathways are there to get from pyruvate to proprionate?
4
What happens to the production of proprionate if ruminants are fed a high concentrate diet?
- Increases
- Also produce lactate
- lactate is strong acid, strong effect on rumen acidity
How does gassy bloat occur?
- Something blocks are reduces normal eructation
- Physical obstruction
- Cessaction of normal ruminants (ruminal acidosis, vagal iindigestion)
- Gas unable to reach oesophagus e.g. in lateral recumbency
How does frothy bloat occur?
- Eating pasture with high quantity of soluble leaf proteins
- Gassy foam in rumen
- Cannot be removed by eructation
What is absorbed from the forestomach?
- VFAs
- Ions
- Water
Where does the majority of absorption take place in the ruminant?
- The rumen-reticulum
What histological feature do all of the forestomachs have in common?
- All have keratinised stratified squamous mucosal epithelium
- Non-glandular
Briefly describe the histological appearance of the omasum
- Mucosa
- Submucosa
- Continuous muscularis mucosa
- Serosa
Briefly describe the histological appearance of the reticulum
- Mucosa
- Submucosa
- Discontinuous muscularis mucosa
- Serosa
Briefly describe the histological appeance of the rumen
- Mucosa
- Submucosa
- No muscularis mucoa
- Serosa
What features of the abomasum make an LDA possible?
- Shape
- Gas filled
- Not tightly fixed
- Attached to greater and lesser omentum
Explain how an LDA may occur
- After calving
- Space in abdomina cavity once calved
- Abomasum can move
- Gas trapped in abomasum so lifts under rumen up on the left side most commonly
