Abstract: An ingestible bolus configured to be maintained in a stomach of an animal may be formed from a substantially cylindrical enclosure shell. Ballast weight and a power source may be disposed therein. The ballast weight may be configured to cause the bolus to be maintained in contact with a stomach wall of the animal when disposed therein. The bolus may comprise sensors to measure one or more animal characteristics, a transmitter in wireless communication with an animal monitoring system, a memory unit to store measured characteristics and bolus configuration data, and processor to control the operation of the bolus components. The transmitter may be in communication with an antenna, which may be formed as a trace on an antenna circuit substrate, such as a printed circuit board (PCB). The antenna may be separated from the sensors, processors, and transmitter to prevent and/or reduce interference and/or coupling therebetween.