I found several threads questioning how to read RFID chips in cats, dogs etc. For different reasons, but no result so far. European system is using 134kHz, but cheap readers use 125kHz. By example RDM6300 can read only a certain type of tags.
I was able to connect RDM6300 directly to arduino input, without using the "intelligence" of the module. So I have time coded signal at the Arduino, ready for analysis. Reading distance is small now, but I think 1cm or more can be realized.
Unfortunable I'm not good enough in programming that. Would be great if still anybody else is interested in that matter to start a project?