References

Statistical Justification Of Animal Numbers

From the Guide, 
“The following topics should be considered in the preparation of the protocol by the researcher and its review by the IACUC:
… justification of the species and number of animals proposed; whenever possible, the number of animals and experimental group sizes should be statistically justified (e.g., provision of a power analysis; see Appendix A, Experimental Design and Statistics)” 
http://www.nap.edu/catalog.php?record_id=12910