T9 data logger (20.7 mm diameter, 140 mm length and weighted 230 g) in assembled (Fig. 1a) and unassembled form (Fig. 1b); parts from left to right: threaded cap, 1/2 AA Lithium metal battery (3.6 mV), metal capsule which house the data logger, SRpH-102 pH sensor, pH sensor slip cap, and above a USB serial interface cable. Flexible white PVC tube (Fig. 1c), 230 cm total length, 26 mm and 33 mm for internal and external diameters respectively, used to orally insert T9 data logger into reticulum and rumen ventral sac, and a thin metal stem used to push data loggers inside PVC tube.
 

28-day rumen pH measurements in calf using T9 data loggers L1 (grey), L2 (red), L3 (green), and L4 (yellow) inserted at d0, d7, d14, and d21 respectively. Calculated pH are means of 15 min pH measurements registered at 5 min interval.