The ML325 is designed for animals which have a heart rate range of 18 to 450 BPM. The heart rate of a mouse is usually above the measurement limit of the Oximeter Pod. Hence ML325 can't be used to measure SPO2 in mice.
Detailed Specifications of the Oximeter Pod can be found here.
For further technical assistance with this or any other issue, please contact ADInstruments Technical Support by clicking HERE.