Continuous monitoring of rumen pH - a case study with cattle

The use of a new pH probe for continuous rumen pH measurement was investigated in a preliminary study in cattle during a 10-day period. Two cannulated non-pregnant dairy cows were used together with two autonomous stomach probes, containing a commercial microelectrode and a reference-electrode with a pressure-equalizing system. By feeding diets with changing composition it was thought to provoke marked changes in rumen pH. Probes were programmed to sample pH and temperature every 30 s. During the entire experimental period, three daily rumen fluid samples were collected via the cannula as close to the probe as possible. Upon removal of probes, final calibration revealed only minor drifting of electrodes, that was significantly lower than results obtained during previous work with continuous measurement of gastric pH. After drift correction, the calculated absolute error of respective probe measurements for 11 sampling events was on average 0.08 pH for cow 817 (maximum 0.085 pH) and 0.14 pH for cow 686 (maximum 0.146 pH). pH measured by gastric probe was on average lower (i.e. more acid) than pH determined by tube sampling, with a mean difference of 0.33 pH (maximum 0.54) and 0.05 pH (maximum 0.5) for cow 817 and cow 686, respectively. The present prototype may thus play an important role in the development of a telemetric device for continuous monitoring of rumen pH in cattle and potentially other ruminants.