Steroids are known to reduce sperm production (any google search will yield a lot of BS plus some legitimate sites that refer to published studies on the relationship between steroids and fertility).
I fathered two children (both healthy, thank god) while taking on average of 400- 600mg a week (American Cypionate, from Walgreens) so I know the dosing was accurate - so I believe the part about test not being as effective in white males.
Partial excerpt of one study is presented below. Note that the text mentions test as contraceptive is not as effective in white males.
The men in the Chinese study received monthly injections of a form of testosterone known as testosterone undecanoate (TU).
Lead researcher Yi-Gun Gu, MD, of Beijing's National Research Institute for Family Planning tells WebMD that while the contraceptive was found to be highly effective in the study, TU alone is not likely to be used in non-Asian populations.
Asian men seem to respond well to testosterone as a form of contraception, while studies in white men have shown it to be much less effective.
The reasons for this are not clear, but Gu tells WebMD that any hormonal birth control developed for non-Asian men is likely to include another hormone -- progestin.
Studies have shown the testosterone-progestin combination to be very effective in suppressing fertility in white men.
The Chinese men in Gu's study took monthly injections of 500 milligrams of TU in tea seed oil for 30 months.