By: A. Riasi (PhD in Animal Nutrition & Physiology) Advanced Digestive Physiology (part 3) Isfahan University of Technology Isfahan, Iran

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

 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

 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. Ruminoreticular wall structure

 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

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

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

 The innervations of fore stomachs: Vagal nerves (10:1 afferent/efferent ratio) Splanchnic nerves (3:1 afferent/efferent ratio) Innervations and the receptors

 The vagal nerves transmit sensory information from two known kinds of sensory receptors: Tension receptors Epithelial/mucosal receptors Innervations and the receptors

 The splanchnic nerves transmit sensory information from: Serosal receptors Possibly tension receptors Innervations and the receptors

 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

 Two types of contractions are identified: Primary contractions Secondary contractions 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 Ruminoreticular motilities

 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

 When i ngesta 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. 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. 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. Ruminoreticular motilities

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

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

 The principal inputs to the gastric centers are from: Forestomachs Abomasum Duodenum by way of vagus nerves Ruminoreticular motilities

StimulusEffectProjectionsReceptors

StimulusEffectProjectionsReceptors

StimulusEffectProjectionsReceptors

 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

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

 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

 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. 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. 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 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. Rumination and its components

 Sensory information from digesta that is perceived in pillars: Digesta texture Digesta consistency Rumen fill Rumination and its components

o Four phases of a rumination cycle: o Regurgitation o Remastication o Reinsalivation o Reswallowing o Regurgitation starts with an inspiration effort. Rumination and its components

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

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

o Slower and more regular rate in remastication phase Rumination and its components

o The rate and duration of rumination chewing are controlled: o The texture (coarseness) o Quantity of the food Rumination and its components

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

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

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

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

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

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

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

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

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

o The grinding and pelleting of forages can reduce emissions by 40%. o Dietary fats have the potential to reduce CH4 up to 37%. Strategies for lower methane emission