Ok...........just read a study that was done on Stallions (no.....not the lab)
Stallions were given exogenous (not in the body) test, Deca-Durabolin - nandrolone decanoate - , and winstrol
Changes in sperm number and quality were noted.......and changes in Leydig Cell function were also noted.....
Its the Sertoli and Leydig cells that are the culprits behind "shut down"......these are the cells that are affected by lh - leutenizing hormone - (from the pituitary) after receiving signals (GnRH) from the hypothalamus......
The only damn conclusion I could find was that...."changes are USUALLY reversible in time" (doesn't say if its irreversible)
Average time length was 3 months to a year (very vague)
No mention was made of compounds to restore natural test production (HCG - human chorionic gonadotropin - , etc)
The only other thing mentionable is that steroids are contra-indicated (not recommended) if the stallion is to breed.......on juice notable decrease in scrotal width etc...etc....etc.....
Very GOOD question.......