Seems like a bit of a gamble if it's usable, but it looks standard and manufacturer dependent. http://en.wikipedia.org/wiki/Microchip_implant_(animal)

As an interesting side note there is a great reference to constructing your own RFID reader ... I might pull out my breadboard and have a play around. I could hook up the heater to turn on when a particular dog sits in it's bed ... or open the doggy flap.

Ooops! I might scratch that idea due to cancer risks of continuous chip activation:

Skip the Chip: RFIDs Could Cause Cancer | Wired Science
Chip Implants Linked to Animal Tumors - washingtonpost.com