Technical note: the use of a telemetric system to continuously monitor ruminal temperature and to predict ruminal pH in cattle.

The objective of this study was to compare a telemetric monitoring system to an existing in situ methodology (conventional system) of monitoring ruminal temperature and to validate its use to detect changes in ruminal pH (RpH). Four nonlactating, ruminally cannulated Holstein dairy cows (760 +/- 30 kg of body weight, mean +/- standard deviation) housed in a tie-stall facility were used in the study. The experiment was conducted during the month of May and the recorded ambient temperature was 8.0 +/- 2.0 degrees C (mean +/- SD). The cows were fed a diet consisting of chopped mixed hay (MH; 11.3% crude protein, 59.7% neutral detergent fiber, 17.3% nonfiber carbohydrate, 3.1% ether extract, and 11.3% ash; dry matter basis) during wk 1 and were gradually switched to a high-grain (HG) diet (11.6% crude protein, 30.2% neutral detergent fiber, 50.7% nonfiber carbohydrate, 3.0% ether extract, and 6.0% ash; dry matter basis) during wk 2. A conventional system that utilized an indwelling electrode was used to monitor RpH and ruminal temperature (RT(C)) during d 6 and 7 of each week. The indwelling electrode was attached to a telemetric bolus and ruminal temperature (RT(T)) was logged into a personal computer. The daily mean, minimum, and maximum RpH and duration (min/d) RpH <6.2 were 6.39 +/- 0.04, 6.10 +/- 0.05, 6.66 +/- 0.03, and 107 +/- 50 during MH feeding (wk 1) and 5.84 +/- 0.03, 5.35 +/- 0.05, 6.35 +/- 0.03, and 1,257 +/- 40 during HG feeding (wk 2), respectively, and were different across diets (week effect). Ruminal pH did not decrease below 5.6, 5.8, and 6.0 during MH feeding; mean duration of RpH <5.6, <5.8, and <6.0 during HG feeding was 279 +/- 149, 611 +/- 139, and 894 +/- 101, respectively. Mean daily RT(C) increased from 37.5 degrees C +/- 0.1 in wk 1 to 38.6 degrees C +/- 0.1 in wk 2; there was also an increase from wk 1 to wk 2 in minimum and maximum daily RT(C) and durations (min/d) of RT(C) >38.0, >38.2, >38.4, and >38.6 degrees C. These increases were not detectable with the telemetric system. Ruminal temperature obtained by the conventional system was 0.68 degrees C +/- 0.005 lower than RT(T) during MH feeding (wk 1), whereas RT(C) was 0.04 degrees C +/- 0.004 higher than RT(T) during HG feeding (wk 2). Daily minimum RpH was associated with maximum daily RT(C) and RT(T) during MH and HG feeding (R(2) = 0.88 and 0.43, respectively). There was a high association between low RpH and high ruminal temperature, with the highest associations being between duration (min/d) of RpH <6.0 and duration of RT(C) >39.0 degrees C (R(2) = 0.68) and RT(T) >39.2 degrees C (R(2) = 0.72). Unlike the telemetric system, the conventional system requires cow cannulation; therefore, the current study provided a noninvasive alternative for measuring ruminal temperature and the prediction of RpH. Additional studies are needed to develop an algorithm that accounts for diet type, seasonal variation in temperature, and core body temperature to predict subacute ruminal acidosis effectively on farm.