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

RUMINAL CONTRACTIONS

Contractions of rumen

• Cyclic, spontaneous contractions occur in the first three compartments. Frequency of cycle varies with the type of activity. Three types of activity prevails normally during
  • resting
  • eating
  • ruminating
• Resting activity is the contractile activity of the stomach when the animal is neither eating nor ruminating. During rest, cyclic motility is less rhythmic with low frequencies.
• Eating: During feeding, strength of contractions and frequencies of contractions are greatly increased.

Cycle of contraction during feeding follows a pattern

• Cycle of contraction begin at reticulum.
• Two contractions occur during feeding or at rest.
• First contraction is mixing contraction  and is weak.
• Second contraction is evacuation contraction which is strong. 
• Between these two contractions, a complete relaxation of reticulum occurs.
• Third contraction follows the second strong contraction during rumination. This third contraction is the strongest of the three and is referred to as extra or regurgitation contrction  of the reticulum.
• Regurgitation of the bolus occurs at the peak of this contraction
• Primary functions of biphasic/triphasic contraction of the reticulum are,
  • To direct the flow of liquid into the cranial sac of rumen.
  • To direct low density digesta into the dorsal sac.
  • To regulate liquid ingesta flow from the ruminoreticulam to the omasum.
  • To assist in regurgitation by flooding the cardia by the ingesta.

Ruminal contractions

• During second contraction of the reticulum, cranial sac of rumen also contracts.
•  Cranial pillars start contracting and form a barrier between the cranial and caudal rumen.
• At the end of the contraction of cranial sac the ingesta in the cranial sac are pushed into relaxed reticulum. At this point, vigorous contraction of   entire rumen pillars, sac and other parts of rumen occur to mix the ingesta well with rumen fluid.
• This rumen contraction is said to be primary and secondary contractions occuring in the frequency of 6-8 contractions / 5 minute. Cardia is always submerged in the liquid ingesta, gets cleared prior to eructation by contraction of pillars of the rumen and walls of the dorsal sac.
• Bubble of gas transferred from dorsal sac to the cardia cranially. This process occurs during reticular relaxation corresponding to the time of contraction of pillars of the rumen.