[Methods for the determination of pH value and redox potential in the rumen fluid of adult cattle].

pH sticks and pH meters were tested to determine ruminal pH and mV meters in order to measure the redox potential in rumen contents. Rumen pH can be determined by reading pH sticks left in rumen liquor or immediately after removal. Differences between pH sticks and a reference method accounted for 0.01-0.48 pH units, depending on the pH stick used and the pH range of the ruminal contents (pH < 6, 6-7, > 7). Ruminal pH is accurately measured by the pH meters pHep and GPHR (y = -0.22 + 1.03x, or y = 0.15 + 0.97 x). By using a mV meter the redox potential in rumen liquor can be determined 10 min after start of measurement. Results determined with the mV meter GPHR showed a mean difference of 10-23 mV, those determined with ORP a mean difference of 131-202 mV in comparison with a reference method. There is no linear correlation between the data of the mV measurements and the data of the methylene blue reduction test in ruminal contents (y = -328.5 - 0.003 x; p = 0.652). Therefore these data may not be in used in the same manner for rumen liquor diagnosis.