Anatomy of the Ruminant Digestive Tract

1
Anatomy of the Ruminant Digestive Tract
2
Taxonomy of Ruminants

• Subclass Ungulata
• Order Artiodactyla
• Suborders
• Ruminantia
• Families
• Tragulidae
• Chevrotain, mouse deer
• Giraffidae
• Giraffes
• Cervidae
• Deer, moose
• Bovidae
• Largest family (120 species)
• Pronghorn, african antelope, bison, buffalo,
  cattle, goats, sheep
• Tylopoda
• Family
• Camelidae
• Camels, Llamas

3
Domesticated ruminant species

• 2.8 billion animals
• 2.2 billion of these are cattle and sheep
• Domesticated ruminants outnumber wild ruminants
  by 101
• Major domesticated ruminant species
• Cattle
• Sheep
• Goats
• Buffalo
• Reindeer
• Yak

4
Classification of ruminants by feeding preference

• Classes of ruminants
• Concentrate selectors
• Intermediate feeders
• Roughage grazers

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Concentrate selecting species

• Properties
• Evolved early
• Small rumens
• Poorly developed omasums
• Large livers
• Limited ability to digest fiber
• Classes
• Fruit and forage selectors
• Very selective feeders
• Duikers, sunis
• Tree and shrub browsers
• Eat highly lignifies plant tissues to extract
  cell solubles
• Deer, giraffes, kudus

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Intermediate feeding species

• Properties
• Seasonally adaptive
• Feeding preference
• Prefer browsing
• Moose, goats, elands
• Prefer grazing
• Sheep, impalas

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Roughage grazing species

• Properties
• Late evolved
• Generally larger rumens
• Slows retention times
• Less selective
• Digests fermentable cells wall carbohydrates
• Classes
• Fresh grass grazers
• Buffalo, cattle, gnus
• Roughage grazers
• Hartebeests, topis
• Dry region grazers
• Camels, antelope, oryxes

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Advantages of pregastric fermentation

• Make better use of alternative nutrients
• Cellulose
• Nonprotein nitrogen
• Ability to detoxify some poisonous compounds
• Oxalates, cyanide, alkaloids
• More effective use of fermentation end-products
  including
• Volatile fatty acids, microbial protein, B
  vitamins
• Decrease in handling undigested residues
• In wild animals, it allows animals to eat and run

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Disadvantages of pregastric fermentation

• Fermentation is inefficient
• Energy
• Loss Amount ( of total
  caloric value)
• Methane 5-8
• Heat of fermentation 5-6
• Relative efficiency is dependent on the diet NDF.
• Protein
• Protein
• Some ammonia resulting from microbial degradation
  will be absorbed and excreted
• 20 of the nitrogen in microbes is in the form of
  nucleic acids
• Ruminants are susceptible to ketosis
• Ruminants are susceptible to toxins produced by
  rumen microbes
• Nitrates
  Nitrites
• Urea
  Ammonia
• Nonstructural carbohydrates Lactic acid
• Tryptophan
  3-methyl indole
• Isoflavonoid estrogens estrogen
• Coumestans

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The ruminant digestive tract

• Lips
• Range from short, relatively immobile in
  nonselective grazing species to very mobile
  (prehensile) in selective grazing or concentrate
  selecting species

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Ruminant teeth

• Dental formula for cattle and sheep
• Jaw
• Upper Lower
• Incisor 0 4
• Canine 0 0
• Premolar 3 3
• Molar 3 3
• Outstanding characteristic
• Upper jaw is wider than lower jaw
• Ruminants animals chew in a lateral(grinding)
  motion on one side of mouth at a time
• Needed to increase surface area of feed particles
• Chewing primarily done during rumination in
  grazing species
• Results in premolar and molar teeth becoming
  concave and beveled
• Upper jaw fits lower jaw.

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Tongue

• Structure
• Muscle covered with a mucus membrane
• Shape varies from being short and piston-like to
  long and slender
• Uses
• Aid in chewing and forming boluses
• Aid in drinking
• Prehension of feed
• Covered with rough, hook-like papillae that
  assist in grasping feed
• Important in nonselective grazing species
• Taste
• Taste buds located on
• Fungiform papillae distributed across tongue
• Vallate papillae found on the back of the tongue
• More numerous than monogastric species
• More numerous on nonselective grazing species

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Taste in ruminants

• 
  Calves
• Sucrose, xylose
  Select
• Fructose, glucose
  Select
• Lactose, maltose
  Indifferent
• Saccharin
  Indifferent
• Acid
  Intolerant
• Alkali
  Tolerant
• Salt
  Tolerant
• 
  Mature cattle
• Sweet
  Strong preference
• Sour
  Mild preference
• Salt
  Strong preference
• Bitter (alkaloids)
  Strong rejection
• Believed that taste is primarily used for food
  avoidance by grazing species while concentrate
  selecting species select on the basis of smell.

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Pharynx

• Structure similar to monogastrics
• Involved in rumination and eructation

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Esophagus

• Involved in rumination
• Differences from monogastric esophagus
• Circular and longitudinal muscles are striated
  muscle along the entire length
• Provides greater strength
• Allows some voluntary control
• Funnel shaped
• Positioned between lungs
• Mucous membrane is comprised of stratified
  squamous epithelial tissue
• Contains 3 sphincters
• Pharyngo-esophageal
• Diaphragmatic
• Cardiac
• Slit-like
• 1 long
• Sphincters active in rumination and eructation

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Regions of the ruminant stomach

• of mature
  ___Volume, l___
• __volume__ Cattle
  Sheep
• Rumen 80
  60-100 9-18
• Reticulum 5
• Omasum 5-8
  6-10 1-2
• Abomasum 5-8
  5-8 2
• Full capacity of the reticulorumen is only used
  in animals fed low quality roughages. Only 60 to
  70 of the total capacity is used in animals fed
  high quality roughages.

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The ruminant stomach
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Structures within the reticulorumen

• Folds
• Areas of tissue dividing the reticulum and rumen
  into different compartments
• Functions
• Mixing and particle sorting
• Prevent fluid from reaching the cardia during
  eructation
• Pillars
• Highly muscled areas of the rumen that form
  grooves on the outside of the rumen
• Contains blood vessels, lymph, and nerves
• Functions
• Contractions

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Structures within the reticulorumen

• Papillae
• Finger-like structures (10mm x 2 mm) covering the
  rumen wall
• Particularly well-developed in ventral portion of
  the rumen
• Few present on pillars in roughage-selecting
  species, but more evenly distributed across rumen
  in concentrate-selecting species
• Function
• Increase absorptive surface for VFAs.

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Structure of the rumen wall

• Non-secretory stratified epithelium covers was of
  reticulum, rumen, and omasum
• Layers
• Stratum basale
• Columnar epithelium with .5 um between cells
• Hemidesmosomes connect to basement membrane
• Nuclei
• Numerous mitochondria
• Stratum spinosum
• Oval-shaped
• Desmosomes connect cells with tonofibrils for
  nutrient transport
• Nuclei
• Fewer mitochondria
• Stratum granulosum
• Flat cells
• Connected by tight junctions
• Nuclei and mitochondria degenerate
• Stratum corneum
• No nuclei or mitochondria
• Tough layer of horny mucopolysaccharide

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Parakeratosis (Incomplete keratinization of the
rumen wall)

• Occurs in ruminants fed high grain diets for
  relatively long periods
• Symptoms
• Thickening of the horny layer (Hyperkeratosis)
• Incomplete keratinization
• Absence of the stratum granulosum
• Retained nuclei in keratinized cells
• Particularly bad on papillae
• Papillae shorten and thicken
• Increased number of branched papillae
• Debris collects in interpapillary spaces causing
  lesions
• Bacteria (Sphaeromonas necrophorus and
  Cornybacterium pyrogenes) enter blood stream and
  form liver abscesses
• Cause
• High concentrations on VFAs, particularly butyrate

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Effects of butyrate concentration on structure of
rumen epithelium

• Low concentrations
• Metabolized to ketones in the epithelium causing
  anoxia
• Stimulates blood flow
• Increases insulin concentration
• Stimulates DNA synthesis
• Increases normal epithelial growth

• High concentrations
• Increases insulin concentration
• Stimulates DNA synthesis
• Inhibits mitosis
• Incomplete maturation of epithelium

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Blood circulation to and from the ruminant stomach

• Supply
• Abdominal aorta
• Celiac-mesenteric trunk
• Arteries
• Common hepatic
• Right ruminal
• Left ruminal
• Left gastric
• Drainage
• Veins
• Reticular
• Right ruminal
• Left ruminal
• Omasal-abomasal
• Portal vein
• Liver

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Factors increasing blood flow to the rumen

• Carbon dioxide in epithelium
• Volatile fatty acids
• Feeding
• Sight or smell of feed (slight)

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Innervation of the rumen stomach

• Vagus nerve
• Involved in both sensory and motor pathways
• Controls contractions of reticulum and rumen,
  rumination, and reflex of the reticular groove
• Sphlanchic nerve
• Minor role in contractions
• Intrinsic nerve
• A rich ganglionic plexus is present in the
  subepithelial region of all compartments of the
  stomach ranging in cells 18 to 40 um in diameter
• Small cells innervate reticular groove, reticulum
  and pillars of the rumen
• Larger cells innervate abomasum
• Functions
• Vasodilatory
• Some control on muscle contractions

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Sensory receptors of the reticulorumen

• Simple nerve endings
• All afferent vagal fibers
• Few receptors in the sacs of the rumen

• Epithelial receptors
• Found near basement membrane in reticulum,
  cranial sac, and longitudinal pillars
• Stimuli
• High threshold distension
• Liquid movement
• Volatile fatty acids
• Rapid acting (mechanoreceptors) or Slow acting
  (chemoreceptors)
• Action
• Inhibit contractions

• Tensions receptors
• Most common
• Found in muscle layers in reticulum,
  reticuloruminal fold, cranial sac, and lips of
  reticular groove
• Excited by low thresholds of distension or
  contractions
• Slow acting response
• Action
• Increase contractions and salivation

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Omasum

• Lies to right of rumen
• Entrance is the reticulo-omasal orifice
• 1 inch slit in cattle
• Lined with small papillae
• Controls particle of digesta leaving
  reticulorumen
• Round organ containing 100-150 flat parallel
  sheets (laminae) covered with conical papilae
• Because of sheets, omasum has 1/3 of the surface
  area of the stomach in cattle and 10 of the
  stomach surface area in sheep
• Sulcus omasi
• Direct route for digesta from the reticulo-omasal
  orifice and omaso-abomasal opening
• Fills by reticular contractions and aspiration

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Functions of omasum

• Filter large particles
• Diameter of particles, mm
• gt5
  3-5 2-3 1-2 lt1
• 
  
• Rumen 2.5
  9.6 20.1 35.1 32.7
• Reticulum 2.4
  8.5 17.9 34.0 37.3
• Omasum .1
  .8 5.9 25.4 68.0
• Abomasum .7
  2.5 7.4 24.6 64.7
• VFA absorption
• 43 to 77 of VFAs entering or 10 of total
  produced
• 85 of VFAs produced are absorbed before abomasum
• Exchanged for Cl-
• Improves efficiency of absorption
• Prevents buffering of the abomasum
• VFAs are strong buffers with a pK of 4.6
• Abomasum functions at pH 2
• Water absorption
• 30 to 60 of water entering
• Magnesium absorption

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Regions of the abomasum
Cardiac
Epithelial
Fundic
Pyloric
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Lining of the different regions of the abomasum

• Fundic region
• Contains gastric glands lined with secretory
  columnar epithelium
• Chief cells
• Secrete pepsinogen
• Continuous
• Parietal cells
• Secrete hydrochloric acid
• Variable
• Pyloric region
• Stratified squamous epithelium
• Secrete mucus

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Surface of the abomasum

• Arranged in 10 to 17 folds
• Functions
• Increase surface area
• Increase approximately 7 times
• Allows greater acid and pepsin secretion
• Prevents stratification of feeds
• Allows for mixing of digesta and enzymes
• Regulate flow

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Secretion of the fundic region

• Composition
• pH 1.05 to 1.32
• Ionic (mEq/l)
• H Variable,
  up to 124
• Na
  Variable, 21 to 167
• Cl-
  138 to 172
• Enzymes
• Pepsinogen
• Converted to pepsin by HCl
• Lysozyme
• Lyses bacteria
• Secretion
• 30 to 35 l/day in cattle
• Amount of HCL secreted to keep pH lt 3
• Pepsinogen secretion is constant
• Factors that increase fundic secretion
• Presence of digesta
• Factors that stimulate rumen motility stimulate
  gastric secretion
• Peak secretion of occurs 45 to 90 minutes after
  feeding

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Motility and digesta flow in the abomasum

• Filled by contractions of the reticulorumen
• Empties by contractions confined to the pyloric
  region
• Flow from the abomasum
• Greatest prior to and during feeding
• Lowest flow occurs immediately after feeding
• Ingesta remains in abomasum for 1 to 2 hours
• As much as 10 backflows into abomasum
• Factors affecting abomasal motility
• Isotonic HCO3- in duodenum increases flow, while
  hypertonic HCO3- in duodenum decreases flow
• Duodenal distension decreases flow
• Long chain fatty acids inhibit abomasal motility
• Acts through duodenal hormone, cholecystokinin
• Lactic acid in duodenum inhibits ruminal motility
  and, therefore, abomasal filling
• Acts through duodenal hormone, secretin
• Increased dietary fiber decrease abomasal flow
• Hyperglycemia decreases abomasal flow
• May contribute to left abomasal displacement

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Regions of the small intestine

• Length, ft
• Cattle Sheep
  Digesta pH Functions
• Total 90-150 60-110
• Duodenum 3-4 2-3
  2.7-4 Enzymes
• 
  pH change
• 
  Flow reg.
• Jejunum 60-100 -
  4-7 Enzymes
• 
  Absorption
• Ileum 30-50 -
  7-8 Absorption
• 
  Variable Fermentation
• Rate of pH increase slower than monogastrics
• Better for peptic activity
• May limit pancreatic protease and amylolytic
  activity

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Pancreatic secretion

• Secreted with bile in the common bile duct of
  sheep
• 1 ft from pylorus
• Secreted in the pancreatic duct of cattle
• 3 ft from pylorus
• Amounts secreted
• 2.2 4.8 l/day (Cattle)
• .3 to .4 l/day (Sheep)
• Composition
• pH 7.2-7.8
• Ionic (mEq/l)
• Na 135-165
• K 4-5
• Cl- 110-126
• HCO3- 15-30
• Enzymes
• Amylase
• Lipase
• Proteases
• Trypsinogen converted to Trypsin

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Activity of pancreatic enzymes

• Concentration of enzymes in pancreatic juice
  comparable to monogastrics
• Activity may be limited by
• Less juice secreted/kg BW
• Low digesta pH
• High rate of passage
• Limited activity particularly a problem for
  intestinal digestion of starch escaping ruminal
  digestion.
• On high grain diets, intestinal starch digestion
  may be as low as 48 (1kg).

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Factors affecting pancreatic secretion

• H in duodenal digesta (HCL or Lactic acid)
• Increases volume and HCO3- concentration
• No effect on enzyme secretion
• Acts through duodenal hormone, secretin
• Fat in duodenal digesta
• Slight increase in volume
• Large increase in enzyme activity
• No effect on HCO3- concentration
• Acts through duodenal hormone, cholecystokinin

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Bile

• Secreted with pancreatic juice in the common bile
  duct of sheep
• Secreted in the bile duct of cattle about 2 ft
  from pylorus
• Amount
• 500-1500 ml/day in sheep
• Composition
• Ionic
• 
  mEq/l
• Na
  154
• K
  7
• Cl-
  122
• HCO3-
  23
• Lipid
• Bile salts (Sodium taurocholate)
• Phospholipids (Phosphotidylcholine)
• Factors increasing secretion
• Bile salts in the duodenum
• HCl in the duodenum
• Through secretin
• Fat in the duodentum

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Small intestinal secretions

• Duodenum
• Secretion from the Brunners glands
• pH 6.7
• Contains small amounts of amylase and
  ribonuclease
• Jejunum and Ileum
• Composition
• Ionic (mEq/l) Upper jejunum
  Lower Ileum
• Na
  136 135
• K
  8 9
• Cl-
  134 105
• HCO3-
  12 42
• pH
  7.1 8
• Enzymes
• Enzymes
• Lactase (in young)
• Maltase
• Isomaltase
• Dipeptidases
• Highest activity in upper to mid-jejunum

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Digesta flow in the small intestine

• Controlled by
• Duodenal hormones
• Enteric nervous system in sub-mucosal and muscle
  layers
• Flow by peristaltic contractions
• Go both directions
• May result in more rapid passage of large
  particles than small particles and liquids

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Large intestine structure

• Size
• 
  Rumen volumeLI volume
• Roughage selectors
  15-301
• Concentrate selectors
  6-101
• Structure
• Cecum
• Blind sac
• 25-25 cm long x 5-7 cm diameter (Sheep)
• Colon and Rectum
• Large tube with longitudinal folds
• No villi

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Large intestine functions

• Fermentative digestion
• Bacteria similar to rumen, but no protozoa
• LI digestion may account for as much as
• 27 of cellulose digestion
• 40 of hemicellulose digestion
• 10 of starch digestion
• Only important in conditions that increase the
  amount of fermentative carbohydrate entering the
  LI
• Increased rate of passage of forages
• High grain diets
• May account for as much as 17 of total VFA
  absorption
• VFAs are efficiently absorbed, but primarily used
  as energy source for mucosa cells

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Large intestine functions (Cont.)

• Absorption of ammonia-N
• May account for as much as 30 to 40 of the net
  transport of N into body fluid
• Absorbed N may be used for
• Synthesis of nonessential amino acids
• Recycling of N to the rumen
• Important on low protein diets
• Regulated by
• Increased by increasing N concentration of diet
• Decreased by increasing the amount of
  carbohydrate fermented in the large intestine.
• Mineral absorption
• Na, K, Ca, P, Co, Mn, Mg, Cu, Zn, Cl
• Water absorption
• 90 of water entering the LI