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Effect of Rumen Insufflation on Ruminal Contraction Rate in Sheep¹

University of California^,2, Davis 95616

Abstract

Rumen motility trials were conducted on sheep fitted with rumen cannulas. The tracheal transection technique was used to ascertain eructation in order to identify secondary rumen contractions.

Increases in intrarumen pressure resulted in a linear increase in primary contraction frequency at pressures below approximately 10 cm HOH and a suppressing effect at pressures exceeding this level. Secondary contraction frequency increased linearly with increasing intrarumen pressure. The frequency of total rumen contractions increased as intrarumen pressure increased

Nitrogen, compressed air, a carbon dioxide-methane gas mixture (60:40) and human expired air were used during the insufflation trials. The presence of carbon dioxide in the gases used during insufflation resulted in a significant increase in primary contractions at intrarumen pressures exceeding 10 cm HOH. Gases containing carbon dioxide resulted in a lower secondary contraction frequency than those gases free of carbon dioxide and consequently a lower total rumen contraction frequency.

For there to be a difference in the frequency of primary and secondary contractions caused by different insufflation gases and pressures suggests separate centers for these types of contractions. There is probably a maximum rumen contraction rate that is dictated by refractory periods in the motility centers and/or musculature of the rumen. Within the contraction rate limits, reciprocal innervation of centers controlling primary and secondary contractions probably occurs.

In view of the findings, it becomes necessary to consider the influence on gastric centers of the gases produced in the rumen, in addition to stimuli arising from rumen presso- and mechanoreceptors.

¹ The technical assistance of Joan Garrett, Paul Fisher and Jim Evans is gratefully acknowledged.

² Department of Animal Physiology.

³ Department of Veterinary Surgery.