I would recommend to check ICH S5(R2) guideline (http://www.ich.org/products/guidelines/safety/article/safety-guidelines.html) and the relevant OECD guideline, e.g. OECD 443 (https://www.oecd-ilibrary.org/environment/oecd-guidelines-for-the-testing-of-chemicals-section-4-health-effects_20745788?page=1).
Please be aware that you need detailed knowledge on testes/ovaries histomorphology in order to be able to do staging.
I strongly recommend the suggested answer of Dr. Geertje Lewin ,it is very important!!! This is one of the most frequent cites of high value to present docs,ti Regulatory authorities in this regard!