Evaluation of indwelling monitoring technologies for measuring reticulorumen pH in cattle

We compared reticulorumen pH measurements determined using smaXtec boli (SMAX; smaXtec Inc., Graz, Austria), Moonsyst boli (MOON; Moonsyst International, Kinsale, Republic of Ireland), and a handheld pH meter (METER; PH8500 pH/mV Meter, Apera, Columbus, OH) over time and during an ex vivo acidosis challenge. Eight ruminally cannulated heifers were used for 6 consecutive 21-d periods. On day 0, SMAX and MOON were placed in the reticulum of each heifer to continuously measure ruminal pH. On day 20 of each period, pH of ruminal digesta samples collected from 4 locations within the rumen were measured with METER prior to feeding and 2, 4, 6, 8, 12, 18, and 24 h post-feeding. Over the 126-d, ruminal pH was lesser for MOON than METER in every period (P ≤ 0.01) with the difference becoming larger in periods 4 through 6 (treatment × period, P < 0.01). Measurements of pH with SMAX were greater (P < 0.01) than METER from periods 1 to 3 and period 6. On day 21 of each period, boli were removed and placed sequentially in pH 4 and 7 solutions, each for 3 h. In pH 4 solution, a treatment × period interaction (P = 0.02) was observed where MOON and SMAX yielded measurements that were not different from pH 4 (P ≥ 0.13), except in period 6. Similarly, in pH 7, a treatment × period interaction (P < 0.01) was observed where MOON yielded measurements less than pH 7 (P ≤ 0.05) in periods 4 to 6 whereas pH measurements with SMAX were greater than 7 (P ≤ 0.05) in periods 1 to 3. Boli were then placed in a container of strained ruminal fluid, and pH was measured using SMAX, MOON, and METER. Subsequently, vinegar was added to the ruminal fluid to simulate an acidosis challenge and pH was measured. The change in pH in response to vinegar addition as measured by METER was considered the true response. During the acidosis challenge, there were no treatment × period interactions (P = 0.34), pH measurements from MOON were similar (P = 0.36) to pH measurements from METER, and pH measurements from SMAX were greater (P < 0.01) than those from METER. Overall, ruminal pH measurements determined using SMAX and MOON drifted over time. During an acidosis challenge, MOON detected changes in pH similar to METER which may suggest that MOON could be capable in detecting acidotic events. Conversely, indwelling ruminal pH measurements determined using SMAX were more closely related to METER throughout the experiment.