Radio frequency identification (RFID) is one of the forefronts of technologies that have found widespread use and the ability to track objects easily from a distance, make it advantageous within other automatic identification systems. RFID systems, which have been used for many years in animal identification and follow-up, have recently been used to track the data (such as pH and temperature) in the rumen. One of the problem is body tissues weakens the signal when the device is used inside the rumen. In this study, we tried to model how UHF signals of RFID tags used as pH bolus weaken after it comes out of the inner body of animal. Preferred RFID tags are operating at 434 MHz (UHF) and CST simulations are verified by real measurements. The signal is taken stronger at the left side of the animal because the amount of tissue on the left side of the animal is less than other sides. The weakest signals are taken at right side with dense organs.