By: A. Riasi (PhD in Animal Nutrition and Physiology) Isfahan University of Technology Advance Digestive Physiology (part 5)

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

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

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

o Rumination is centrally mediated by the "gastric centers" in medulla oblongata and the ventral hypothalamic area. o Tactile stimulation of the reticular and ruminal epithelia is a powerful stimulus for rumination. o The carniocaudal pillar complex harbors receptors monitor the volume and texture of ruminoreticular digesta. Rumination and its components

o Sensory information from digesta that is perceived in pillars: o Digesta texture o Digesta consistency o 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 is 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% however the costs associated with this practice may be prohibitive. o Dietary fats have the potential to reduce CH4 up to 37%. Strategies for lower methane emission