It would be a great project if someone could somehow figure it out.
In addition to your tid bit on your little experiment I have a few questions.
Are you referring to BPs? And if so are you certain with an adult female eating mice that she is getting enough food in general? It would take a very large amount of mice to match even the gram weight of an adult rat. Just wondering if you can say in confidence that it wouldnt effect your outcome of results.
I always switch my new BPs to rats if they are on mice, its such a pain to feed an BP adult mice IMO.