VPB 121: Veterinary Physiology - II (2+1)

ERUCTATION

• It is the expulsion of fermentation gases like CO₂ and methane that has accumulated in the rumen.

• Receptors for eructation reflex are the tension receptors located in the reticulum, cardia, and cranial rumen sac, which are stimulated by accumulation of gas.
• Vagus provides both afferent and efferent fibres. Eructation  centre is present in medulla.
• Volume of gas produced in rumen of a dairy cow is ½ to 1 litre/minute. The gas layer is moved cranially by the secondary contraction of the dorsal sac.
• The cardia and lower oesophageal sphincter open, and the gas enter into the relaxed oesophagus. By an antiperistaltic wave in the oesophagus and elevation of soft palate the gas is expelled through the mouth.
• Free gas found at the top of the ingesta in the dorsal rumen sac move cranially and ventrally to the cardia. Cardia remains closed by contact with watery ruminal content. Cardia gets free of ingesta during the contractions of dorsal sac, cranial pillar and caudal pillar.
• Accumulation of gas in the dorsal sac is the primary stimulus of eructation.  Increase in the pressure in the dorsal sac of the rumen increases the eructation frequency and amount of gas expelled.
• Eructation occurs once in two ruminoreticular contractions. Inhibition of eructation isobserved during blokage of ruminoreticular contraction.   Block of eructation leads to bloating of the rumen, called as TYMPANY which can also happen when gas production is higher than the elimination.
• Rumen distension decreases the lung volume  and alters breathing pattern. Mechanical activity of the diaphragm is inhibited. Oils and non absorbable surfactants are used to treat bloat.
•  Biphasic increase in pressure in the esophagus is observed during eructation. In the first phase, gas enters the esophagus. In the second phase,sharp increase in pressure accompanied by esophageal contraction.
• High grain feeding and feeding of lush alfalfa results in trapping of gases in the rumen called “ feedlot bloat” or “legume bloat”. This is due to formation of foam in the ruminoreticulum which traps many small gas bubbles. This can be prevented by reducing feeding of grains or lush pastures.