193 Evaluation of in-dwelling pH monitoring technologies

We compared ruminal pH measurements determined using smaXtec bolus (SMAX; smaXtec Inc., Graf, Austria), Moonsyst bolus (MOON; Moonsyst International, Kinsale, Republic of Ireland), and handheld pH meter (METER; PH8500 pH/mV Meter, Apera, Columbus, OH) over time and during an ex vivo acidosis challenge. Ruminally cannulated heifers (n = 8) were used for 6 consecutive 21-d periods. On d 0, SMAX and MOON were placed in the reticulum of each heifer and continuously measured ruminal pH. On d 20 of each period, ruminal digesta samples were collected prior to feeding and again 2, 4, 6, 8, 12, 18, and 24 h post-feeding pH was measured with METER. MOON yielder lower (P < 0.01) pH measurements compared with SMAX and METER at all time points. From h 0 to 2 post-feeding measurements from SMAX were similar compared with METER (P = 0.54); however, measurements from SMAX tended to be greater 4 h post-feeding (P < 0.07) and differed at all subsequent timepoints (P < 0.05) compared with METER. On d 21 of each period, boli were removed and placed in a pH 4 and pH 7 solution, each for 3 h. In pH 4 solution, MOON pH measurements did not differ (P > 0.39) from 4 from periods 1 to 5; however, pH measured by MOON in period 6 was less (P < 0.01) than 4. Smaxtec pH measurements did not differ (P ≥ 0.39) from 4 during periods 2 to 5 but was greater (P < 0.01) than 4 in period 6. In pH 7 solution, pH measures with MOON did not differ (P > 0.26) from 7 for period 1 and 2 but declined in period 3 and were less than 7 from periods 4 to 6 (P < 0.05). In pH 7 solution, SMAX measurements varied over time and yielded greater (P < 0.05) than 7 for periods 2, 3, and 6. Subsequently, boli were placed in a container of strained ruminal fluid (6.5 L), and pH was measured for 1 h using SMAX, MOON, and METER. Following, 500 mL of vinegar was added to the ruminal fluid to simulate an acidosis challenge, pH was measured and change in pH detected by SMAX and MOON, relative to METER was determined. With change in pH detect by METER considered the true response, MOON provided a better measurement of the pH decrease than did SMAX, particularly during periods 1 to 3 (P < 0.01). Overall, pH measurements differed between SMAX, MOON, and METER. MOON and SMAX pH measurements began to drift after approximately 100 d. MOON was more accurate than SMAX in detecting a change in ruminal pH, whereas pH measurements over time were more precise for SMAX than for MOON.