Ever since Salem, the American wizarding population has been dangerously low. So MACUSA implements a breeding program. As a powerful wizard with excellent magic genes, Graves is a top stud. It’s his civic duty to impregnate as many bitches as he can, and he does so with pride & enthusiasm. The fertile broodmares are strapped onto breeding benches in optimal position for him to mount and pump full of his seed.

Author’s choice if the people being impregnated are dubcon or noncon, female or male. If mpreg, could be because of magical modification, ABO, or just handwave it - up to you.

Bonus: Dirty talk especially referencing breeding, come inflation, lactation, etc. Can be from Graves and/or the officials overseeing the program.