Lecture 9 - Fatty Acid Metabolism

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Isfahan University of Technology Isfahan, Iran
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Rumen and reticulum properties

• The ruminoreticular fold partially separates the
  reticulum and cranial sac of the rumen.
• Pillars divide the rumen to dorsal and ventral
  parts.

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• The dorsal part of rumen is divided to
• Cranial sac
• Dorsal sac
• Caudodorsal blind sac
• The ventral part of the rumen is divided to
• The ventral sac
• The caudoventral blind sac

Rumen and reticulum properties
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Ruminoreticular wall structure

• Highly vascularized connective tissue core is in
  the mucosal layer of the finger-like papillae
• Epithelium is involved in the absorption of
  short-chain fatty acids.

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• In the reticulum the mucosal layer contains
  laminae.
• Conical projections (papillae) are found on the
  surface of laminae.
• The stratified squamous epithelium of reticulum
  also absorb short-chain fatty acids.

Ruminoreticular wall structure
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Ruminoreticular wall structure

• The reticulum has a role in mechanical digestion
  of food.
• Myenteric plexus can be found between the
  muscularis externa layers.

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Blood circulation of forestomachs

• Celiac artery supply the blood flow to
  forestomach and the most part of abomasum.
• The venous blood drains into the hepatic portal
  vein.

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Innervations and the receptors

• The innervations of fore stomachs
• Vagal nerves (101 afferent/efferent ratio)
• Splanchnic nerves (31 afferent/efferent ratio)

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Innervations and the receptors

• The vagal nerves transmit sensory information
  from two known kinds of sensory receptors
• Tension receptors
• Epithelial/mucosal receptors

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Innervations and the receptors

• The splanchnic nerves transmit sensory
  information from
• Serosal receptors
• Possibly tension receptors

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• The movements serve to
• Mix the ingesta
• Aid in eructation of gas
• Propel fluid and fermented foodstuffs into the
  omasum.
• A cycle of contractions occurs 1 to 3 times per
  minute.

Ruminoreticular motilities
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Ruminoreticular motilities

• Two types of contractions are identified
• Primary contractions
• Secondary contractions

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Ruminoreticular motilities

• Typical primary cycle consist of
• Biphasic (double) contraction of the reticulum
• Caudally moving monophasic contraction of the
  dorsal ruminal sac
• A contraction of the ventral ruminal sac

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• Secondary cycle may occur and consist of
  sequential contractions of
• The caudoventral ruminal blind sac
• A cranially moving contraction of the
  caudodorsal ruminal blind sac followed by the
  middorsal ruminal sac
• A contraction of the ventral sac.

Ruminoreticular motilities
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Ruminoreticular motilities

• When ingesta enter the foestomach, heavy objects
  fall into the reticulum and lighter material
  enters the rumen.
• Added to this mixture are voluminous quantities
  of gas produced during fermentation.

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Ruminoreticular motilities
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Ruminoreticular motilities

• The forestomachs possess a rich enteric nervous
  system.
• Contractions coordination need the central
  input.
• Motility centers in the brainstem control both
  the rate and strength of contraction via vagal
  efferents.

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Ruminoreticular motilities

• There are also vagal afferents from the rumen to
  the motility centers which allow stretch
  receptors and chemoreceptors in the rumen to
  modulate contractility.

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Ruminoreticular motilities

• Feeble intrinsic contractions responsible for
  the smooth muscle tone in the forestomach wall
  arise from nervous activity in its intrinsic
  nerve networks.

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Ruminoreticular motilities

• The gastric centers do not have spontaneous
  activity and need to be driven by
• Excitatory inputs
• Inhibitory inputs

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Ruminoreticular motilities

• The principal inputs to the gastric centers are
  from
• Forestomachs
• Abomasum
• Duodenum by way of vagus nerves

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Stimulus
Effect
Projections
Receptors
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Stimulus
Effect
Projections
Receptors
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Stimulus
Effect
Projections
Receptors
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• The known sensory receptor mechanisms are
  responsible for the vagal inputs.
• The tension receptors are located in the muscle
  layer of different parts.
• The epithelial receptors are located closed to
  the basement membrane of the luminal epithelium
  of the forestomachs.

Ruminoreticular motilities
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• Conditions inside the rumen can significantly
  affect motility.
• Acidic ruminal contents
• High roughage diet

Ruminoreticular motilities
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• Ruminants are well known for "cud chewing
• It provides effective mechanical breakdown of
  roughage and increases substrate surface area.
• Rumination is a unique characteristic of
• True ruminants (deer, giraffes, and bovidae)
• Pseudoruminants (camels and llamas).

Rumination and its components
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Rumination and its components

• Rumination occurs in resting.
• The highest incidences of rumination occur during
  afternoon and middle of the night.
• Many lactating ruminants ruminate while they are
  suckling their young or are being milked.

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Rumination and its components

• The time spent ruminating by a given animal
  depends on
• The texture of the food
• The amount of food ingested
• Cattle may ruminate from 35 to 80 minutes per
  kilogram of roughage consumed.

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Rumination and its components

• Pharmacological agents have been used to examine
  the physiological mechanisms involved in evoking
  rumination.
• Volatile fatty acids
• Catecholamines
• Gastric hormones
• Opioids
• Autacoids

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Rumination and its components

• Rumination is centrally mediated by the "gastric
  centers located at
• Medulla oblongata
• Ventral hypothalamic area
• Tactile stimulation of the reticular and ruminal
  epithelia is a powerful stimulus for rumination.

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Rumination and its components

• Sensory information from digesta that is
  perceived in pillars
• Digesta texture
• Digesta consistency
• Rumen fill

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Rumination and its components
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Rumination and its components

• Four phases of a rumination cycle
• Regurgitation
• Remastication
• Reinsalivation
• Reswallowing
• Regurgitation starts with an inspiration effort.

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Rumination and its components

• The bolus is carried into the mouth by reverse
  peristalsis.
• Antiperistaltic waves of regurgitation passes
  over the esophagus at a velocity of 0.2 m per
  second.

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Rumination and its components

• In about two seconds, the "retained" bolus has
  the fluid squeezed out of it.
• This fluid is immediately swallowed, and the
  remainder is chewed, reinsalivated, and
  subsequently swallowed.

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Rumination and its components

• Slower and more regular rate in remastication
  phase

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Rumination and its components

• The rate and duration of rumination chewing are
  controlled
• The texture (coarseness)
• Quantity of the food

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Rumination and its components

• The reinsalivation phase of rumination coincides
  with the remastication phase.
• Rumination saliva and ingestion saliva are
  secreted at about the same rate and about 2.5
  times the resting rate.

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Eructation

• Eructation is the physiological process of
  expelling ruminoreticular gases
• Carbon dioxide, 65
• Methan, 25
• Nitrogen, 7
• Oxygen, 0.5
• Hydrogen, 0.2
• Hydrogen sulfide, 0.01.

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Eructation

• The eructation is associated with almost every
  secondary ruminal contraction.
• Eructated gas travels up the esophagus at 160 to
  225 cm per second
• Interestingly, a majority is actually first
  inspired into the lungs, then expired.

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Eructation

• A large portion of the eructated gases is
  inspired and recycled into the organism by
  absorption into the lungs.

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Eructation

• The rumen raft is the site of origin of most of
  the gases of fermentation.
• When dorsal surface of raft splits, releasing of
  free gas into the gas layerand occur.
• Not much of the gas is absorbed, and most must
  be eliminated by eructation.

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Eructation

• If the gas layer reaches the cardia and clear it
  of fluid, the eructation mechanism is evoked.
• Eructation is a vagovagal reflex, with centers
  in the medulla ablongata.
• Mechanical receptors to detect distention are
  present in
• Rumen dorsal sac
• Reticular groove
• Around the cardia and esophagus

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Eructation

• The primary type of rumen contraction always
  follows the biphasic reticular contraction and
  spread caudally.
• In cattle
• 66 with the secondary type of rumen
  contraction,
• 20 with the primary type.

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Eructation

• In sheep
• 3 no dependent rumen motility
• 37 with secondary-type rumen contractions
• 60 with the time with the primary type

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Strategies for lower methane emission

• Increasing the efficiency in which animals use
  nutrients to produce milk or meat.
• Rumen modifiers such as ionophores improve dry
  matter intake efficiency and suppress acetate
  production, which results in reducing the amount
  of hydrogen released.

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Strategies for lower methane emission

• The grinding and pelleting of forages can reduce
  emissions by 40 .
• Dietary fats have the potential to reduce CH4 up
  to 37.