Most elf males should be sterilized, preferably before they reach sexual maturity. Much in the way that a farmer does maintain a whole slew of fertile roosters or bulls. The elf males with appropriate traits (submissiveness, feminine appearance, physical weakness, etc) can be kept intact in the ownership of a licensed breeder. They'll of course be kept in chastity. When a sperm sample is needed, they can be sedated, the sample acquired via prostate manipulation, and put back in chastity. It can then be used to inseminate the elf girl that is to be bred.
The excess sterilized males, if they're feminine enough (we are talking about elves here), can be sold as slave girls as well, although obviously they are an even lower status than the true females. Some human men will enjoy them. Those that aren't attractive enough for that can be used for scientific research, some other forms of entertainment, some forms of skilled labor, or will simply destroyed and repurposed to feed elf-hunting dogs.
Ideally, most domestic elf girls should be sterilized as well, just as we often sterilize our other pets. It prevents any accidents and makes sure the population is controlled. For their own good, really. That being said, I want to stop short of making it mandatory. What separates a good elf girl from a poor one is not always apparent until later on, and it would be a shame if good specimens were discovered only after breeding them was no longer an option. And we don't want to go stomping on people's rights to do with their pet as they please. We do live in a free society, after all.
