This is really going to depend on the sex and age of your animals, how you process/stain your sample, your gating strategy if using flow cytometry or the instrument used to analyze a hematology sample. My recommendation would be to look and see if the analyzer manufacturer can provide you with background ranges. However the best practice is to generate the data yourself from a control cohort using the exact method you are going to use for your experimental samples. This way you know that the data is comparable. Otherwise the differences I mentioned above can skew your ability to interpret the data.