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Effect of lactic acid administration on rumen myoelectrical activity and pressure changes in the sheep Smith, Craig Michael


Pressure changes and myoelectrical activity in the ovine rumen were investigated following the surgical implantation of fluid filled balloon-tipped tygon tubes and paired fine needle platinum electrodes. The correlations among rumen pressure change and myoelectrical spike burst duration, frequency and magnitude data from 447 7 one minute periods were determined in order to select a single reliable quantitative measurement of rumen motility. The results showed that all these parameters accurately reflect activity changes in the rumen. Myoelectrical spike burst duration was shown to be the most sensitive indicator and was used as the criterion for examination of lactic acid induced motility changes. Rumen motility was not affected by intraruminal introduction of 1000 ml of 0.15 or 0.7 M lactic acid at pH 2.0 via permanently implanted cannulae. Intravenous infusion of 2 concentrations of sodium lactate which increased blood lactate levels by approximately 20 mg% and 180 mg% respectively, also had no effect on rumen motility. Infusion of lactic acid solutions (250 ml) 0.15 or 0.7 M (pH 2.0, 4.0 and 6.0) intraduodenally via polyethylene cannulae exerted profound effects on rumen motility. Immediately following ( 1 min) the commencement of the infusion of lactic acid (pH 2.0), a short period of total inhibition of motility occurred which was followed by a rapid recovery of motility to near normal levels despite the continuation of the infusion. These initial short periods of inhibition and recovery continued for up to one hour following termination of infusion. Similar yet somewhat reduced responses were observed upon intraduodenal infusion of the lactic acid solutions at pH 4.0 and 6.0. These results suggest that inhibition of rumen motility in lactic acidosis may be caused primarily by lactic acid produced in the rumen entering the intestine and causing a stimulation of the enterogastric reflexes.

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