Indwelling rumino-reticulum bolus radio beacon

A miniature battery-powered radio beacon attached to a stainless steel bolus housing an osmotic pump is described. When the bolus, of sufficient size and density to be retained in the reticulum, is administered to ruminants the radio signal can be received, using a standard AM broadcast receiver up to a range of 1.5 m. The unit allows making a simple and inexpensive verification that the drug delivery system is still within the rumino-reticulum during long-term drug delivery studies and making an external estimation of the internal anatomic location of the device.