Rumination in sheep. IV. The investigation of some possible control mechanisms

Abstract

Rumination of caged sheep was recorded under conditions of: (a) variable rumen pH, (b) rumen infusions of volatile fatty acids and urea, (c) variable saliva flow to the rumen, (d) mixing of the rumen contents in vivo, and (e) teasing with food. The circadian (24-hr) pattern of rumination after once daily feeding was similar to the pattern of rumen pH change, but no consistent effect of pH per se upon the initiation of rumination was found when rumen contents were replaced with buffered mixtures at pH values ranging from c. 5.10 to 6.95. Rumination, however, tended to be irregular at the lower pH levels. The addition of sodium carbonate to the rumen to prevent a fall in pH after feeding had no apparent effect upon the initiation of rumination. The infusion of volatile fatty acid or urea solutions into the rumen apparently did not affect rumination. Removal of part of the saliva by aspiration during eating, or adding previously aspirated saliva had no effect. The manual mixing of rumen contents by means of a large rumen fistula did not affect initiation of rumination. After teasing with food, one sheep did not recommence ruminating for several hours; another showed practically no reaction; and the remaining two intermediate responses. The initiation of rumination is discussed in relation to these and some other aspects.